Hormonal activity

In early research, prolonged injections of black cohosh extract in rats and mice increased the weight of the uterus and established menstrual cycles in juvenile and climacteric animals.¹² Black cohosh extract demonstrated a selective reduction of serum LH in ovariectomised rats. FSH (follicle-stimulating hormone) and prolactin levels were unchanged. Intraperitoneal administration of black cohosh extract (24 mg dried extract per day) resulted in significant inhibition of LH secretion after the third day. Fractionated extraction of black cohosh and subsequent testing with three fractions indicated that the LH-suppressive substances resided in the dichloromethane extract. The intact glycosidal components of this extract were more active with regard to LH suppression than the aglycone form. Oral administration of the non-hydrolysed extract demonstrated a significant inhibition of LH, although much lower than that achieved by injection.¹³ (This does not necessarily mean the aglycone is inactive, as the glycoside may provide enhanced bioavailability with cleavage of the sugars yielding an active aglycone.)¹⁴

A subsequent study by the same group found serum levels of LH in ovariectomised rats were reduced after intraperitoneal administration of a trichloromethane fraction of a black cohosh methanolic extract, whereas the ethanolic fraction of the extract did not affect LH levels. The trichloromethane fraction also demonstrated an ability to bind to oestrogen receptors in vitro. This fraction was further separated into three subfractions, two of which suppressed LH secretion in vivo and displaced oestrogen in vitro. This indicates that at least two groups of compounds may be responsible for the endocrine activity of black cohosh.¹⁵ One active compound identified was the isoflavone formononetin. However, five more recent studies have failed to detect formononetin in black cohosh,² a fact that casts some doubt on the extract used in the study.

In other early research, water and chloroform fractions prepared from a black cohosh methanol extract were tested in ovariectomised rats by intraperitoneal injection over several days (chronic administration). The chloroform fraction demonstrated a strong LH-suppressing effect after 3 days; the water fraction was inactive. Further fractionation of the chloroform extract led to the conclusion that the LH-suppressive effect of black cohosh extract was caused by at least three different synergistically acting compounds.¹⁶

Another later study in ovariectomised rats showed that a dichloromethane (lipophilic) extract (60 mg subcutaneously for 7 days) produced effects similar to those of oestradiol on LH levels and other biomarkers influenced by oestrogen receptors.¹⁷

Two commercial black cohosh extracts were tested for their ability to compete with oestradiol for antigen binding sites on an antibody (IgG) directed against oestradiol (radioimmunoassay). Both extracts ran parallel with the displacement curve obtained with oestradiol, which supports the presence of oestrogenic compounds in black cohosh.¹⁸ However, no oestrogenic activity was found after oral or subcutaneous administration of black cohosh extract (6, 60, 600 mg/kg) to groups of immature mice and ovariectomised rats respectively.¹⁹

A 50% aqueous ethanolic extract of black cohosh did not bind to oestrogen or progesterone receptors of human breast cancer cell lines (MCF7 and T47D) in vitro (100 μg/mL) and did not affect cell proliferation.²⁰ Similarly, a methanolic extract (200 μg/mL) did not bind to human recombinant alpha and beta oestrogen receptors in vitro.²¹ Gene expression studies in MCF7 cells found that a lipophilic black cohosh extract had no oestrogenic activity, but instead exerted anti-proliferative and pro-apoptotic effects at the transcriptional level.²² (See also below under Effects on human breast cancer cells.)

Only the lipophilic subfraction of a dry, hydroethanolic extract of black cohosh was able to activate the human alpha oestrogen receptor, but neither the total extract nor the lipophilic sub-fraction showed any in vivo uterotrophic effects in 21-day-old rats.²³

One hundred and ten women experiencing menopausal symptoms, who had received no hormone replacement therapy (HRT) for at least 6 months, received either a standardised black cohosh extract or placebo. After 8 weeks of treatment, LH levels were significantly reduced (p<0.05) in the black cohosh group, but FSH was unchanged.¹⁶

Effects on menopausal bone loss

Several studies have indicated that black cohosh might protect against menopausal bone loss (see also under Clinical trials).

An in vitro study investigated the effects of an ethanolic black cohosh extract on bone nodule formation in mouse pre-osteoblast cells.²⁴ The extract did not stimulate osteoblast proliferation, but significantly increased bone nodule formation (500 ng/mL), an effect that was shown to result from enhanced gene expression of osteocalcin and Runx2 (a transcription factor involved in osteoblast differentiation). Interestingly, co-treatment with a selective oestrogen receptor antagonist abolished the effects on gene expression, demonstrating the involvement of an oestrogen receptor-dependent mechanism.

An experimental model was designed to understand the mechanism of action of black cohosh on bone tissue and to compare its effects with oestrogen and testosterone.²⁵ RANK (receptor activator of nuclear factor-kappaB, NF-kappaB) and its ligand RANKL largely regulate osteoclast activity and hence bone breakdown. Crosslaps (or Ratlaps in rats), specifically the metabolic products of bone-specific collagen-1 alpha1, are markers of such bone degradation. When black cohosh, oestradiol and testosterone were given to castrated rats of both sexes, oestradiol and black cohosh reduced levels of RANKL and Ratlaps, the latter parameter only in female rats. The authors suggested that the bone sparing effect of black cohosh is therefore partly mediated by inhibition of RANKL. However, the receptors involved in mediating this effect are not thought to be oestrogen receptors.

In a 35-day study of metaphyseal fracture healing in ovariectomised rats with early stage osteoporosis, the effects of a black cohosh supplemented diet (dried aqueous ethanolic extract, average 24.9 mg/day) was compared with oestrogen treatment (average 0.03 mg/kg/day).²⁶ A high rate of metaphyseal callus formation was observed in the animals receiving black cohosh, but oestrogen improved fracture healing more, with the authors commenting that the 5-week treatment period was possibly too short for black cohosh to demonstrate its full potential.

The triterpenoid glycoside 25-acetylcimigenol xylopyranoside isolated from black cohosh was shown in vitro to potently block osteoclastogenesis induced by tumour necrosis factor-alpha (TNF-alpha) and a related cytokine. The compound was also found to reduce bone loss induced by TNF-alpha in vivo.²⁷

Effects on human breast cancer cells

Because of the potential oestrogen-like action of black cohosh, the issue of its safety in oestrogen-dependent tumours is of significant clinical interest, and a number of studies have been undertaken in an attempt to clarify this issue.

Unlike oestradiol, black cohosh extract did not stimulate growth of mammary tumour cells in vitro. In fact, a dosage of 2.5 mg/mL led to a strong inhibition of proliferation.²⁸ The simultaneous incubation of tumour cells with tamoxifen (anticarcinogenic agent, oestrogen antagonist) and black cohosh displayed a much stronger inhibition of growth than for either substance alone.²⁹ (Oestrogen is contraindicated in patients with oestrogen receptor-positive breast carcinoma, since it promotes the growth of the tumour cells.)

Several other studies have demonstrated that black cohosh does not promote the growth of human breast cancer cells in vitro. A 50% aqueous ethanolic extract (100 μg/mL) did not promote cell proliferation of T47D cells.²⁰ In another study, a methanol-water extract was fractionated. A fraction rich in triterpenoid glycosides inhibited the growth of two human breast cancer cell lines (IC₅₀ values of 10 to 20 μg/mL).³⁰ The same fraction also caused cell cycle arrest at G1 (30 μg/m and G2 (60 μg/mL), suggesting that different compounds are involved in causing cell cycle arrest. The triterpene glycosides actein, 23-epi-26-deoxyactein and cimiracemoside A were shown to be involved in these effects.

In a subsequent gene expression study conducted by the same group, actein was shown to activate transcription factors that enhance apoptosis.³¹ It also repressed cell cycle genes and acted synergistically with two chemotherapy agents, doxorubicin and 5-fluorouracil, in causing growth inhibition of the breast cancer cell line MDA-mB 453.³² The same study also showed that actein enhanced the induction of apoptosis by paclitaxel, 5-fluorouracil and doxorubicin.

A review of the safety and efficacy of black cohosh for cancer patients assessed data from clinical (n=5) and pre-clinical (n=21) studies as well as case reports.³³ The five clinical studies all involved women with breast cancer or a history of the disease. None of the adverse effects reported from these trials (including one case of breast cancer recurrence) was linked to the black cohosh treatment. The authors of the review concluded that black cohosh does not have phyto-oestrogenic activity, appears to be safe for breast cancer patients and may potentially be protective against breast cancer, as it appears to inhibit the growth of tumour cells in vitro (See also under Clinical trials and Toxicology.)

Effects on prostate cancer cells

In vitro studies have demonstrated that black cohosh can inhibit proliferation of prostate cancer cells. In one study, the cell growth inhibitory effects of an isopropanolic extract of black cohosh on androgen-sensitive LNCaP and androgen-insensitive PC-3 and DU 145 prostate cancer cells were investigated. Results showed the extract caused a significant dose- and time-dependent downregulation of all prostate cancer cell lines after 72 h (IC₅₀ values between 37.1 and 62.7 μg/mL). Further, the study demonstrated that the extract killed prostate cancer cells by induction of apoptosis and activation of caspases, regardless of the hormone responsive status of the cells.³⁴

A phenolic compound isolated from black cohosh, petasiphenone, was studied in vitro with regard to its effects on the proliferation of LNCaP cells (incubated with 10 nM oestradiol, 1 nM dihydrotestosterone, or without either) and their secretion of prostate-specific antigen (PSA). A dose-dependent inhibition of the LNCaP cells was observed regardless of hormone treatment, while PSA release was not altered.³⁵

In an in vivo study, a black cohosh extract was tested in immunodeficient mice inoculated sc with LNCaP cells. Inoculation with the prostate cancer cells resulted in formation of solid tumours in 12 of 18 control animals, compared with only five of 18 animals treated with dietary black cohosh extract (2 to 2.8 mg extract/day). After 10 weeks, the amount of tumour tissue in the black cohosh-treated animals was significantly less than in controls. Serum testosterone levels were not significantly affected by the treatment.³⁶

Other activity possibly contributing to menopausal effects

While the nature and degree of any oestrogenic activity of black cohosh remains unresolved, other potential mechanisms of action have emerged. That several mechanisms might be at play in a chemically complex herbal medicine is of course unsurprising.

A commercial black cohosh extract demonstrated in vitro dopaminergic activity in the dopamine receptor D2 assay,³⁷ and there are suggestions that serotonergic effects might play a role in the therapeutic effects of black cohosh. Researchers at the University of Illinois at Chicago working on black cohosh extract did not find evidence of oestrogen receptor binding or oestrogenic effects in animals, but did observe strong binding to several serotonin receptor subtypes in vitro, with partial agonist activity at the 5-HT₇ receptor.³⁸ The same group has also shown that black cohosh acts as a mixed competitive ligand and partial agonist at the human mu opioid receptor.³⁹

Central opioid activity has also been shown in a mechanistic study involving 11 postmenopausal women.⁴⁰ The study employed two methods to examine the effects on central opioid function: naloxone challenge (n=6) and positron emission tomography with a selective micro-opioid receptor radioligand (n=5), before and after 12 weeks of standard treatment with a black cohosh isopropanolic extract (40 mg/day). Treatment did not affect oestrogen levels or spontaneous LH pulsatility, but administration of naloxone (a competitive mu opioid receptor antagonist) caused suppression of mean LH pulse frequency. This was most marked during sleep, when the mean interpulse interval was prolonged by 90 minutes. Positron emission tomography showed significant increases in mu opioid receptor binding potential in parts of the brain involved with emotional and cognitive function.

Because of the close relationship between the central nervous and hormone systems, it is plausible that mechanisms involving serotonergic, dopaminergic and opioid receptors are at least partly responsible for the effects of black cohosh on menopausal symptoms.

Anti-inflammatory and antioxidant activities

Several recent in vitro studies have lent some support to the traditional use of black cohosh in the treatment of inflammatory conditions. An aqueous extract (up to 6 mg/mL) was found to inhibit the generation of nitric oxide in lipopolysaccharide (LPS)-stimulated macrophages in a concentration-dependent manner. The mechanism for this was shown to be the reduced expression of inducible nitric oxide synthase (iNOS) rather than inhibition of iNOS activity. The triterpenoid glycoside 23-epi-26-deoxyactein was identified as the active compound.⁴¹

Another black cohosh compound, cimiracemate A (140 µM), has been shown to suppress the in vitro production of the inflammatory cytokine TNF-alpha induced by LPS in macrophages.⁴²

Aqueous black cohosh extracts (3 and 6 mg/mL) have also been shown to reduce the release of TNF-alpha and the interleukin IL-6 (another inflammatory cytokine) and almost completely block the release of interferon-gamma in LPS-stimulated whole human blood. In contrast, IL-8 (also an inflammatory chemokine) was stimulated. Among five prevalent compounds isolated from the extract, isoferulic acid was found to be responsible for the inhibition of TNF-alpha and IL-6, but not for the stimulation of IL-8.⁴³

Black cohosh showed potent antioxidant activity in the oxygen radical absorption capacity (ORAC) assay in a study that applied a sequential three solvent (ethyl acetate, methanol and 50% aqueous methanol) extraction process and combined the antioxidant activity of the three extracts. Black cohosh was the second most potent of 53 medicinal plants tested, being second only to olive leaf.⁴⁴

Another in vitro study found black cohosh to be an effective scavenger of 1,1-diphenyl-2-picrylhydrazyl free radicals. Nine compounds with activity in this assay were isolated and six of these (methyl caffeate>caffeic acid>ferulic acid>cimiracemate A>cimiracemate B>fukinolic acid) were found to also reduce menadione-induced DNA damage in cultured S30 breast cancer cells.⁴⁵

Other activity

Pretreatment with cimicifugoside inhibited blastogenesis in mouse splenic lymphocytes and brought about a decrease in the number of plaque-forming colonies using sheep erythrocytes (SRBC). The anti-SRBC response in the plaque-forming assay was suppressed in mice after pretreatment by intraperitoneal administration, and delayed hypersensitivity was suppressed after intravenous administration. The immunosuppressive activity of cimicifugoside is directed toward B-cell function, with larger doses being required for suppression of T-cell function.⁴⁶

Black cohosh extract, and several fractions obtained from it, demonstrated hypotensive activity after intravenous administration at 1 mg/kg to rabbits. The hypotensive activity was observed in particular with the resinous part and may be due to actein. A hypotensive effect was not observed in human volunteers (by intravenous administration), although a peripheral vasodilatory effect was evident, even in subjects with peripheral arterial disease.⁴⁷ Oral administration of black cohosh extract (2 g/kg) inhibited 5-hydroxytryptophan-induced diarrhoea in mice.⁴⁸

Menopause

In phytotherapy, black cohosh is predominantly used in the treatment and management of menopausal symptoms. Menopause is the permanent cessation of menstruation and fertility defined as the absence of ovarian follicular activity for at least 12 months. The symptom picture associated with the transition from peri- to postmenopause can range from mild to debilitating, and the duration of symptoms can range from a few months up to 10 years.

Experts on menopause refer to a wide variety of physical symptoms including hot flushes, cardiac complaints, fatigue, vertigo, sweating, muscle pain, muscle spasm, joint pain, urinary incontinence, vaginal dryness and vaginal epithelium atrophy, and psychological symptoms: depression, anxiety, nervousness, irritability, forgetfulness, sleep disturbances and decreased libido. Vasomotor symptoms of hot flashes and night sweats are the most common physical manifestation, occurring in up to 80% of menopausal women.⁵¹ Women who experience vasomotor symptoms are also more likely to suffer sleep disturbances and depressive symptoms and experience a negative impact on their quality of life.

A broad array of treatments including hormone therapy, antidepressant medications, herbal and nutritional therapies, and diet and lifestyle modifications are utilised by women to ameliorate unwanted menopausal symptoms.

Black cohosh is the herbal medicine most commonly recommended for managing psychological and physical symptoms of menopause. Standardised black cohosh extract was used with success in the 1950s and 1960s for the treatment of menopausal symptoms, menstrual disturbances in young women (secondary but not primary amenorrhoea) and symptoms arising from ovarian dysfunction or insufficiency.

Research interest in black cohosh has gained momentum since the publication of the Women’s Health Initiative study in 2002. This study found an association between the long-term use of HRT and increased breast cancer and cardiovascular risk.⁵² As a result of these findings, prescribers and users of HRT began to explore non-hormonal alternatives, the most common being black cohosh. Black cohosh is prescribed alone in a number of proprietary formulas, but is also used in combination with other herbs and nutrients in formulations for menopausal symptoms.

Black cohosh for menopausal symptoms has been investigated extensively in clinical trials, but not all trials have been convincing. This may in part be due to poor trial design, including small sample size and variability in the dose used. Many trials (including several with positive outcomes) have used an extract dose equivalent to 40 mg/day of dried herb, a dose which is low in comparison to the more traditional one recommended in the British Herbal Pharmacopoeia 1983 (0.9 to 6 g/day dried root and rhizome).⁴

A number of recent comprehensive monographs,⁵³ systematic reviews^54,55 and a meta-analysis⁵⁶ have examined the efficacy and safety of black cohosh for menopausal symptoms; this body of literature represents the most rigorous and global assessment of black cohosh currently available.

A systematic review published in 2008 included six double blind, randomised, controlled trials (n=1112) of black cohosh for the relief of menopausal symptoms.⁵⁵ Trials that included women suffering medically induced menopause were excluded. Each of the included trials focused on menopausal symptoms, and used a placebo or a standard drug treatment as control. Three of the six trials used an isopropanolic extract in a daily dose equivalent to 40 mg herb, one trial used 160 mg of a 70% ethanolic extract (equivalent to 5 mg of triterpene glycosides), another used a 58% ethanolic extract equivalent to 40 mg of herb, and the sixth used 6.5 mg of a 60% ethanolic extract. Despite the authors’ conclusion that the evidence for the efficacy of black cohosh was still inconclusive, five of the six trials produced some positive outcomes. Details of these six studies are provided below.

In an early trial, Stoll used a randomised, double blind design in 75 women with symptoms of menopause. The 3-month study compared treatment with black cohosh with conjugated oestrogens and placebo. The Kupperman Menopausal Index (KMI), Hamilton anxiety scale, and proliferation status of vaginal epithelium were the outcome measures, and results demonstrated that black cohosh improved all parameters compared with placebo.⁵⁷

Another 3-month randomised, double blind, multicentre trial involving 62 postmenopausal women also compared black cohosh (equivalent to 40 mg/day), conjugated oestrogens and placebo. Outcome measures included the Menopause Rating Scale (MRS), markers of bone formation and degradation, and endometrial thickness. Results of this trial showed that both active treatments were effective in reducing menopausal symptoms and both had beneficial effects on bone metabolism. Unlike treatment with conjugated oestrogens, black cohosh did not affect endometrial thickness.⁵⁸

Osmers and co-workers conducted a 12-week randomised, double blind, placebo-controlled multicentre trial involving 304 women with menopausal symptoms. Women in the black cohosh group received extract equivalent to 40 mg/day, and the MRS was again the primary outcome measure. The women receiving black cohosh experienced significantly greater improvement in menopausal symptoms, especially hot flushes, compared with the placebo group. Women in early menopause benefited the most.⁵⁹

A multicentre, randomised, placebo-controlled, double blind study was conducted by Frei-Kleiner and co-workers in 122 menopausal women experiencing at least three hot flushes daily. They were treated over 12 weeks with a black cohosh extract (equivalent to 42 mg herb) or placebo. Outcome measures were a weekly score for hot flushes, the Kupperman Index and the MRS. Overall the results showed no significant difference between the two groups. However, significant benefits of black cohosh were evident in women with more severe symptoms (Kupperman Index score of at least 20), and the effects of black cohosh over placebo almost reached significance (p=0.052) for the subgroup comprising perimenopausal women.⁶⁰

In the HALT study, a 12-month randomised, double blind, trial was undertaken with 351 peri or postmenopausal women. They received either black cohosh (160 mg of a 70% ethanolic extract equivalent to 5 mg triterpene glycosides daily), a multi-botanical preparation (alfalfa, chaste tree, dong quai, false unicorn, licorice, oats, pomegranate, Siberian ginseng, boron; 200 mg daily), the multi-botanical plus telephone counselling to increase dietary soy intake, conjugated oestrogens with or without medroxyprogesterone acetate, or placebo. The main outcome measures were frequency and intensity of vasomotor symptoms. The study found no difference between the herbal interventions and placebo at 3, 6 or 12 months, whereas the HRT resulted in a significant decrease in vasomotor symptoms compared with placebo (p<0.001).⁶¹

Bai and colleagues conducted a 3-month double blind, multicentre, non-inferiority trial in China in 244 women with menopausal symptoms. They were randomised to receive either black cohosh extract (equivalent to 40 mg/day) or the synthetic steroid drug tibolone (2.5 mg/day), which has been shown in numerous placebo-controlled trials to be effective in the treatment of menopausal symptoms. The main outcome measures were the KI and the frequency of adverse events. The effects of the two treatments were similar and clinically relevant: in the black cohosh group mean KI decreased from 24.7 at baseline to 11.2 and 7.7 after 4 and 12 weeks, respectively, while the corresponding scores for the tibolone group were 11.2 and 7.5. These results demonstrated that the black cohosh treatment was as effective as tibolone treatment (non-inferiority was statistically significant, p=0.002), with the benefit-risk balance for black cohosh being significantly superior to tibolone (p=0.01).⁶²

A 2010 meta-analysis by researchers at McGill University in Montreal included nine randomised, placebo-controlled trials of black cohosh-containing preparations for menopausal symptoms. Four of the included trials have been reviewed above; the additional five trials used black cohosh in combination with other active ingredients such as St John’s wort, isoflavones, lignans or other herbs. Overall, the authors of this meta-analysis found that six of the nine studies demonstrated a significant effect for the black cohosh-containing intervention over placebo. Combining the data from seven trials, they calculated an estimated improvement in menopausal vasomotor symptoms of 26% (95% CI 11–40%) with black cohosh treatment.⁵⁶ However, the value of comparing different treatments in a meta-analysis is questionable. The five trials of black cohosh in combination with other active ingredients are reviewed below.

The efficacy of black cohosh in combination with St John’s wort was assessed in 89 symptomatic peri- and postmenopausal women in a 12-week double blind, randomised, placebo-controlled, multicentre study. The main outcome measure was the Kupperman Index (KI); biochemical parameters (hormone levels and lipid profiles) and pathology (vaginal atrophy) were also measured. The active treatment consisted of a 264 mg tablet containing 0.0364 mL of extract from black cohosh rhizome (equivalent to 1 mg terpene glycosides) and 84 mg of dried extract from Hypericum perforatum, equivalent to 0.25 mg hypericin. Treatment with the herbal preparation resulted in significantly greater reduction in KI scores after 4 (p=0.002) and 12 (p<0.001) weeks, compared with placebo. There were no other clinically significant differences between the two groups (although HDL levels decreased marginally in the placebo group). The results demonstrated this combination of black cohosh and St John’s wort to be effective in alleviating menopausal symptoms.⁶³

A second study also examined the efficacy of the fixed combination of black cohosh and St John’s wort in women with menopausal symptoms. The double blind, randomised, placebo-controlled study included 301 women experiencing menopausal symptoms with a pronounced psychological component. They were treated with ethanolic St John’s wort extract and isopropanolic black cohosh extract or placebo for 16 weeks. The MRS and the Hamilton Depression Rating Scale were used to measure outcomes. The mean MRS score decreased 50% (0.46 to 0.23) in the treatment group and 19.6% (0.46 to 0.37) in the placebo group, whereas the Hamilton Depression Rating Scale total score decreased 41.8% (18.9 to 11.0) in the treatment group compared with 12.7% (18.9 to 16.5) in the placebo group. The herbal treatment was significantly (p<0.001) better than placebo for both measures.⁶⁴

Another randomised, double blind, placebo-controlled trial in 50 healthy peri- and postmenopausal women assessed a formula containing standardised extracts of black cohosh, dong quai, milk thistle, red clover, American ginseng and chaste tree berry for 3 months. Frequency and intensity of menopausal symptoms were monitored by way of a structured questionnaire, administered weekly. Biochemical tests, breast checks and transvaginal ultrasonography were also performed. Women receiving the herbal formula reported a significant and progressive reduction in menopausal symptoms over the placebo group. After 3 months there was a 73% decrease in hot flushes and a 69% reduction of night sweats, with a decrease in symptom intensity and improved sleep quality in the herbal group. Complete cessation of hot flushes was reported by 47% of women in the herbal group compared with 19% in the placebo group. Vaginal ultrasonography, hormone levels (oestradiol, FSH), liver enzymes or thyroid-stimulating hormone showed no change in either group.⁶⁵

A study by an Italian group evaluated the short-term effects of a combination of black cohosh with isoflavones and lignans on acute menopause-related symptoms in postmenopausal women using a double blind, randomised, placebo-controlled design. Eighty healthy, postmenopausal women were randomly assigned to receive either the combination formula or a placebo (calcium supplement). The groups were similar at baseline, but after 3 months of treatment the KI was significantly lower (p<0.05) in the black cohosh-phyto-oestrogen group compared with the placebo group.⁶⁶

A supplement containing black cohosh and soy isoflavones was studied in a randomised, placebo-controlled, double blind multicentre 12-week trial involving 124 women who experienced at least five vasomotor symptoms every 24 h. They were randomised to receive daily either the black cohosh-isoflavone supplement or placebo. The modified KI and the Greene Climacteric Scale were used to measure outcomes. After 6 and 12 weeks of treatment, all scores had improved in both groups compared with baseline, and there was no statistically significant difference between the supplement and placebo groups.⁶⁷

A large scale, observational study comparing the effect of black cohosh alone and black cohosh in combination with St John’s wort also deserves mention. The study was conducted in Germany between March 2002 and March 2004, and included 6141 women with any menopausal symptoms and who had not taken HRT in the 4 weeks preceding the study. The participants had mostly mild to moderate symptoms and were treated with recommended doses of black cohosh monotherapy (isopropanolic extract equivalent to 20 mg herb per tablet) or combination therapy (isopropanolic extract of black cohosh equivalent to 30 mg herb plus St John’s wort extract equivalent to 245 to 350 mg herb per tablet). The treating physician determined the choice and dose of treatment. Patients were evaluated at baseline, 3 and 6 months, with some patients electing to continue for a further 6 months. The primary outcome measures were the MRS and the PSYCHE sub-score of the MRS. In women receiving black cohosh monotherapy, total MRS scores declined from baseline by 0.10 and 0.14 after 3 and 6 months, respectively, whereas the corresponding decreases were 0.12 and 0.18 for the combination therapy, suggesting that the addition of St John’s wort provided an additional effect. Similarly, the changes on the PSYCHE sub-score were significantly greater with the combination therapy than with black cohosh alone (p<0.001). However, the data are potentially confounded by the fact that baseline scores for the two groups were not equal and doses were not fixed. Improvements were sustained by both treatments at 6 and 12 months.⁶⁸

In a small double blind, placebo-controlled trial, black cohosh had no significant anxiolytic activity in women with anxiety disorder due to menopause.⁶⁹

Breast cancer patients with menopausal symptoms

Black cohosh used in the management of hot flushes in patients with breast cancer has also been studied in clinical trials. Two such studies, with conflicting results, are summarised below. In an open label randomised trial, 136 breast cancer survivors (35 to 52 years) were treated over 12 months with a black cohosh extract for hot flushes caused by tamoxifen therapy. The patients had all been treated with segmental or total mastectomy, chemotherapy and radiation therapy and were receiving tamoxifen 20 mg/day (n=46) or tamoxifen 20 mg/day plus black cohosh (equivalent to 20 mg herb per day) (n=90). Results revealed those in the intervention (black cohosh) group had fewer and less severe hot flushes compared with controls. After 12 months’ treatment nearly half of those receiving black cohosh were completely free of hot flushes, while 24.4% of the black cohosh group versus 73.9% of the tamoxifen group were still reporting severe hot flushes (p<0.01).⁷⁰

An earlier randomised, placebo-controlled trial involving 85 breast cancer survivors stratified for tamoxifen use (59 on tamoxifen and 26 not on tamoxifen) did not find any effect of black cohosh over placebo in terms of number and severity of hot flushes. The dose of black cohosh used in this trial was not provided in the report. Subjects completed a 4-day hot flush diary at baseline and at 30 and 60 days, as well as a menopause symptom questionnaire at baseline and at the final visit. FSH and LH levels were measured in a subset of patients at the first and final visits, but no significant differences were detected between the two groups.⁷¹

Bone loss prevention

Bone mineral loss (osteoporosis) is a major consideration for postmenopausal women, as it is a major age-related source of morbidity and mortality. A 12-week double blind study in 62 postmenopausal women compared the effects of a black cohosh preparation (equivalent to 40 mg herb per day), conjugated oestrogens or placebo on bone metabolism and other parameters. Black cohosh and conjugated oestrogens were found to have beneficial effects of similar magnitude on bone metabolism. Black cohosh treatment significantly increased serum levels of bone-specific alkaline phosphatase, indicative of increased osteoblast activity. Treatment with conjugated oestrogens, however, did not produce this effect, but appeared to decrease the activity of osteoclasts. Hence, while the net effects on bone of the two treatments were comparable, it appeared that the mechanism of action differed.⁵⁸

This effect of black cohosh on bone density parameters appears to be mild and, on current evidence, it could not be credibly proposed as a treatment for osteoporosis. However, it probably should play a role as part of an appropriate diet, supplementation and lifestyle regime for the prevention of osteoporosis in both men and women, especially those with borderline osteopenia.

A study in 128 women found that, while an exercise programme favourably affected bone health, adjuvant supplementation with black cohosh (40 mg/day) did not enhance this effect.⁷² Perhaps a higher dose might have been necessary for this experimental design.

Arthritis

In a randomised, double blind, placebo-controlled trial, 82 male and female patients with osteoarthritis and rheumatoid arthritis received a licensed over-the-counter (OTC) herbal medicine (two tablets/day) or placebo for a period of 2 months. The formula contained black cohosh, willow bark, guaiacum resin, sarsaparilla and poplar bark. Although there was no significant difference between the two groups for most symptoms, a significant decrease (p<0.05) in pain scores occurred for those taking the herbal formula. Many patients reported a decline in health related to the cold, damp, windy weather experienced near the end of the trial, which may have altered the findings. A relative improvement in mood scores was also noted for those taking the herbal tablets.⁷³ The authors of this study advised that the results may not be relevant to the activity of black cohosh, as the formulation predominantly comprised herbs containing salicylate derivatives.

Infertility

Unexplained infertility is typically defined as the failure to conceive over 1 year for couples exhibiting no apparent abnormalities. It is believed to occur in 15% to 30% of couples trying to conceive. Medically it is often treated with the fertility drug clomiphene citrate, which can be used in conjunction with gonadotropins to help trigger ovulation. In a controlled clinical trial, patients with unexplained infertility who had not responded to clomiphene therapy alone were randomly divided into two groups. The first group was given black cohosh dry extract at 120 mg/day (500 mg of dried root) from days 1 to 12 of the cycle. Both groups received clomiphene from days 3 to 7 and human chorionic gonadotropin (HCG) injection close to ovulation. All were recommended to have timed intercourse every day for the corresponding week. Endometrial thickness was measured on the day of the HCG injection and was found to be significantly thicker for the group receiving black cohosh (8.9±1.4 mm versus 7.5±1.3 mm, p<0.001). Serum progesterone concentrations measured in the luteal phase (days 21 to 23) were significantly higher in the black cohosh group (13.3±3.1 ng/mL versus 9.3±2.0 ng/mL, p<0.01). The pregnancy rate was also significantly higher for the group given black cohosh (36.7% versus 13.6%, p<0.01), even after one treatment cycle. These results suggest a benefit to including black cohosh in the medical management of infertility.⁷⁴

A follow-up trial by the same group using a similar design found that follicular-phase black cohosh exerted a better activity than ethinyloestradiol in terms of improving cycle characteristics in 134 infertile women treated with clomiphene citrate. No significant difference was found regarding clinical pregnancy rates.⁷⁵

General side effects

High doses of black cohosh can cause a frontal headache, with a dull, full or bursting feeling. This headache is the most characteristic effect observed when giving even therapeutic doses.⁹⁸ A review published in 2000 found that mild gastrointestinal upset was the most frequent minor adverse event reported in clinical studies (average of 5.6% of patients across five studies). Other minor adverse events reported in clinical studies included headache, vertigo, weight gain, mastalgia, heavy feeling in the legs and a stimulant effect. Vaginal bleeding has also been reported.²

Two reviews published in 2003 confirm that adverse events with black cohosh are rare, mild and reversible. Gastrointestinal upsets and rashes are the most common adverse events. There is record of a few serious adverse events, including hepatic and circulatory conditions, but causality could not be determined.^99,100 Details of some of the case reports follow.

A case was reported in 2001 of a woman diagnosed with grade 1 endometrioid adenocarcinoma of the endometrium ‘whose history was notable for extensive use of supplemental phytoestrogens’. Herbs included chaste tree, dong quai, black cohosh and licorice.¹⁰¹ No causality was demonstrated.

A 45-year-old woman who had been taking separate bottled products of black cohosh, Vitex agnus-castus and evening primrose oil for 4 months had three nocturnal seizures within a 3-month period. The patient had also consumed one to two beers 24 to 48 h prior to each incident.¹⁰² It was not established whether the herbal preparations caused the seizures.

A 26-year-old woman presented at a hospital with chest pain. Her heart rate and blood pressure dropped temporarily during the course of monitoring. Her urine digoxin level was ‘elevated’ at 0.9 ng/mL (but within the normal therapeutic range – 0.5 to 2.0 ng/mL). However, she was not taking digoxin. In addition to the contraceptive pill, she was taking a herbal preparation containing black cohosh, skullcap (Scutellaria lateriflora), lousewort (Pedicularis canadensis), hops (Humulus lupulus), valerian (Valeriana officinalis) and cayenne pepper (Capsicum annuum). The product was not available for analysis. The chest pain had started during her shift as a topless dancer, during which she had consumed four alcoholic drinks, but no illicit drugs.¹⁰³ This study inappropriately speculated on ‘digoxin-like factors’ with cardiotonic activity claimed to be ‘commonly’ found in herbal teas. The source of the patient’s symptoms remains a mystery, but factors that interfere with digoxin assays, yet are without cardiotonic activity, have been reported in some herbs. (Refer to the Ginseng (Eleutherococcus senticosus) monograph by way of example.)

A case report exists of a 54-year-old woman who developed severe asthenia and high blood levels of creatine phosphokinase (230 to 237 U/L), lactate dehydrogenase (504 to 548 U/L) and total cholesterol, while taking a supplement derived from black cohosh for the management of vasomotor symptoms related to menopause. Notably the woman had previously taken the product for 12 months with no alteration in biochemistry and had restarted the product after a 3-month break. The black cohosh tablets contained 20 mg of dried rhizome and root extract. No other cause could be identified for her symptoms and she was advised to discontinue the product, after which a progressive normalisation of biochemical parameters and improvement in clinical symptoms occurred.¹⁰⁴

A case report described a 56-year-old woman diagnosed with cutaneous pseudolymphoma after taking a black cohosh product for 12 months. The localised erythematous plaques on her arms and legs appeared after 6 months and completely disappeared with withdrawal of the product for 3 months.¹⁰⁵

Other adverse reactions attributed to black cohosh use include cutaneous vasculitis¹⁰⁶ and coagulation activation with fluid retention (secondary to a transient autoimmune hepatitis).¹⁰⁷

Liver injury

On the 9 February 2006, the Australian TGA announced the following:

On July 18, 2006, the Medicines and Healthcare Products Regulatory Agency (MHRA) in the UK issued a press release stating that all black cohosh products sold there should carry the following label warning: ‘Black cohosh may rarely cause liver problems. If you become unwell (yellowing eyes/skin, nausea, vomiting, dark urine, abdominal pain, unusual tiredness) stop taking immediately and seek medical advice. Not suitable for patients with a previous history of liver disease.’

Notwithstanding the Australian TGA’s claim at the time concerning the number of cases of liver damage linked to black cohosh (which include the adverse reaction reports filed with the UK MHRA and other health authorities) only five papers or letters had been published purporting to demonstrate a link between black cohosh (Actaea racemosa) ingestion and subsequent liver injury. It is important to closely examine these published reports since, because of the process of peer review, these represent the best-documented evidence of any association with liver injury. The first publication, from doctors at the Princess Alexandra Hospital in Brisbane, Australia, described six patients with evidence of severe hepatitis that was linked to taking a range of herbal products.¹⁰⁸ Two of these patients were taking black cohosh, although one was also taking other herbs including skullcap, a herb which can be substituted by Teucrium species, a known hepatotoxic genus.¹⁰⁹

The one case attributed to black cohosh alone (Case 1) was truly dramatic. Of the cases reported, the most serious illness occurred in this 47-year-old woman who was taking black cohosh for menopausal symptoms. She required liver transplantation even though, according to the publication, the patient had been taking the black cohosh for just 1 week. Histological examination of her liver confirmed severe hepatitis and early fibrosis. The patient did not exhibit eosinophilia and had no signs of any systemic disturbance. Serology for hepatitis A, B and C was negative, but rechallenge with the herb was not performed ‘for ethical reasons’. The dose of black cohosh taken was not specified, neither was the product.

The second publication, also from Australia, describes a 52-year-old woman with acute liver failure (Case 2).¹¹⁰ She had been taking an herbal formula containing 1:1 liquid extracts prescribed by a pharmacist. Black cohosh 1:1 was 10% of the mixture and the daily dose of the combination was 7.5 mL twice a day. The patient underwent successful liver transplantation. Although the authors stated that: ‘Extensive investigation excluded other recognised causes of liver failure’, they provided no details of what these investigations were. Analysis by the TGA was said to confirm the presence of golden seal, black cohosh and Ginkgo in the herbal mixture. Other stated ingredients were ground ivy and oats seed.

The phenomenon of idiosyncratic hepatic reactions to drugs is well documented. It also appears that this reaction does occur to certain herbs, for example chaparral (Larrea tridentata) and germander (Teucrium species). By definition, such reactions are rare and unpredictable and are not dose related. There are two types of idiosyncratic hepatic injury: hypersensitivity and aberrant metabolism. The former develops 1 to 5 weeks after exposure to the drug and, since it is immune-mediated and acute, also involves a systemic reaction including rash, fever and eosinophilia. The latter takes weeks to months to develop and symptoms are confined to the liver. Diagnosis of drug-induced idiosyncratic liver injury (DILI) is very difficult and relies largely on circumstantial evidence. Factors taken into account include a temporal association, exclusion of other possible causes, a consistent latency period to those described above, presence or absence of hypersensitivity (systemic) features, positive response to drug removal (dechallenge), positive response to rechallenge and a positive lymphocyte stimulation test (this last factor is quite controversial). Complicating this is the fact that DILI can mimic every known human liver disease.¹¹¹ There are many confounding factors that could lead to incorrect associations between ingested medications or herbs and idiosyncratic liver injury. Many viruses that cause liver disease are still to be identified¹¹² and there are no tests for them. Even known viruses are not always tested for. For example, a Dutch study published this year found that hepatitis E virus was a significant cause of unexplained hepatitis.¹¹³ Occult coeliac disease has been suggested as a cause of unexplained raised ALT and AST.¹¹⁴ Rare liver diseases may not be excluded.^115,116 Other environmental factors could be implicated.

The experience of a liver transplant unit highlights some key issues behind the history and incidence of severe acute hepatitis (fulminant hepatic failure, FHF). All adult cases of FHF presenting to the Victorian Liver Transplant Unit (Australia) from 1988 to 2002 were analysed. Eighty patients (mostly female) were referred, at a rate of approximately one case per million population per year. Mean age was about 38 years. Most cases were due to paracetamol poisoning (36%) or idiopathic hepatitis (34%).¹¹⁰ Only five of the 80 cases were classified as drug induced, making this causality a rare factor. Other main causes included hepatitis A (three cases), hepatitis B (eight cases) and Wilson’s disease (six cases). The 27 cases (34%) of hepatitis due to unknown causes (idiopathic) is a surprising rate. These cases are also described as non-A non-B hepatitis, since patients are not positive for hepatitis A or B. In the USA one study found that the most common cause of FHF was non-A non-B (idiopathic) hepatitis.¹¹⁷ (Note that this US study was published in 1995, well before the dramatic rise in herbal use in that country.) Presumably unidentified infectious or environmental factors could cause these cases of idiopathic hepatitis. However, the authors of the Australian study state: ‘The strong female predominance of cases argues against a viral cause and raises the possibility that hormonal factors are involved, or that the condition is linked to autoimmune liver diseases. There is clearly a need for large, detailed, multicentre epidemiological studies, to provide further clues to a possible aetiology/ies of this syndrome.’

The demographics of idiopathic hepatitis (female, late 30s to early 50s) and black cohosh use strongly overlap. Hence, there is a distinct possibility that some patients who develop idiopathic hepatitis might also be coincidentally taking black cohosh. The herb could then be mistakenly attributed as the cause.

Since these initial series of cases attributing idiosyncratic hepatotoxicity to black cohosh, more cases have been reported. There have also been several publications analysing these and the earlier case reports, especially from the team headed by Teschke.

In 2009 the group rigorously analysed all 69 reported cases (at the time) and found no likelihood of causality in 68.¹¹⁸ Most cases were marred by confounding variables, misreported data and a lack of critical information.¹¹⁹ In particular, there was a lack of identification of the herb involved in the initial cases.¹²⁰

Of high relevance here are the findings of Health Canada. From January 2005 to March 2009, Health Canada received six domestic reports of liver adverse reactions suspected of being associated with black cohosh. Analysis of three products associated with these reports revealed that they did not contain authentic black cohosh. Their phytochemical profiles were consistent with the presence of other related herbal species. A review of the authenticity of all licensed products containing black cohosh resulted in the voluntary withdrawal of several products not containing authentic black cohosh, including the products reported in four of the adverse reaction cases.¹²¹

Studies in black cohosh users have also sought to understand its impact on the liver. A prospective, longitudinal study recruited 100 healthy postmenopausal women from a hospital in Egypt. The women received black cohosh extract (40 mg/day) for relief of menopausal symptoms and were followed up for 12 months. Eighty-seven women completed the study, which included evaluation of total hepatic blood flow and liver function. The study sought to investigate potential mechanisms of hepatotoxicity: compromise of blood flow to the liver or a direct toxic effect on liver cells. The following results were obtained after 12 months of treatment:

A meta-analysis of five trials involving 1117 women found no evidence that the isopropanolic extract of black cohosh has an adverse effect on liver function.¹²³

Anti-inflammatory and related activity

Laboratory studies on Boswellia extract and boswellic acids have demonstrated their ability to both prevent and relieve inflammation. Anti-inflammatory and antiarthritic activity was demonstrated in several models:¹² carrageenan-, histamine- and dextran-induced oedema, carrageenan-induced pleurisy,¹³ adjuvant arthritis, formaldehyde- and bovine serum albumin (BSA)-induced arthritis¹⁴ and sodium urate gouty arthritis. Oral doses of Boswellia extract from 25 to 200 mg/kg were typically tested. The anti-inflammatory effect was not affected by removal of the adrenal glands, indicating the pituitary-adrenal axis was not involved. No significant activity occurred in cotton pellet-induced granuloma, which is more sensitive to steroidal than non-steroidal anti-inflammatory agents. In the developing adjuvant polyarthritis model, boswellic acids significantly reduced the development of secondary lesions. The reversal of syndromes of established arthritis indicated that it could control damage arising from immunological mechanisms.¹²

In adjuvant arthritis, administration of Boswellia extract or boswellic acids decreased the urinary excretion of connective tissue metabolites¹⁵ and had a beneficial effect on glycohydrolases and lysosomal stability.^16,17 Treatment also reduced the degradation of glycosaminoglycans. From these results it is likely that Boswellia has beneficial effects in inflammatory conditions by suppressing proliferating tissue and preventing the degradation of connective tissue.¹⁸ Anti-inflammatory activity was also observed for B. carterii extract (450 to 900 mg/kg/day for 7 days, oral) in inflammation induced by complete Freund’s adjuvant.¹⁹ Topical application of a boswellic acid ointment demonstrated a dose-dependent anti-inflammatory effect in both acute and chronic experimental models, including croton-oil- induced mouse ear oedema and adjuvant arthritis in rats.²⁰

Oral administration of boswellic acids reduced the development of 24 h delayed-type hypersensitivity reaction and complement fixing antibody in mice.²¹ Oral administration of boswellic acids, particularly AKBA, before treatment with galactosamine/endotoxin significantly reduced serum enzyme activity and potential liver damage in mice.²² (This is a model of increased leukotriene synthesis.) A pain-relieving activity was reported for Boswellia extract,^23,24 but this finding was not confirmed in later studies.¹² Weak antipyretic activity was, however, observed.¹² AKBA (50 to 200 mg/kg, oral doses) produced a dose-dependent and significant analgesic effect in several different experimental models of nociception and potentiated the analgesic effect of selective cyclo-oxygenase inhibitors such as nimesulide.²⁵

Conflicting results were observed in experimental models of gastrointestinal inflammation. One study found that Boswellia extract did not ameliorate symptoms of colitis in mice,²⁶ whereas in another AKBA and high-dose Boswellia extract significantly reduced tissue injury in rats with experimental ileitis.²⁷ AKBA was also found to confer protection in experimental murine colitis induced by dextran sodium sulphate, possibly by interfering with P-selectin-mediated recruitment of inflammatory cells.²⁸

Boswellic acids were described as belonging to the group of slow-acting antiarthritic medications and inhibited latex-induced rat paw inflammation at oral doses of 50 to 100 mg/kg.²⁹ Unlike conventional non-steroidal anti-inflammatory drugs (NSAIDs), ulcerogenic effects were not detected for Boswellia extract in animal models, and the extract even exhibited a protective effect on experimentally induced ulcers in rats.³⁰ Other side effects of NSAIDs, such as prolonged gestation and parturition and diarrhoea, were not observed for the boswellic acids.¹²

Mechanism of action

The clinically relevant anti-inflammatory mechanisms for Boswellia are not fully understood. It appears to possess activity across a wide range of inflammatory diseases. While earlier studies have suggested the basis for anti-inflammatory activity is 5-lipoxygenase inhibition, this understanding has been challenged in recent times.

In early research, boswellic acids significantly inhibited the stimulated release of leukotrienes from intact human neutrophils, with AKBA being the most potent.³¹ Boswellia extract also reduced the formation of leukotrienes by inhibiting the enzyme 5-lipoxygenase in vitro.³²

Boswellic acids appeared to exert a specific in vitro inhibitory activity on 5-lipoxygenase, with little effect on cyclo-oxygenase (which produces prostaglandins) or 12-lipoxygenase, although some inhibitory activity on both these enzymes has been recently found in human platelets.³³ The mechanism of action is therefore quite distinct from conventional NSAIDs, which inhibit prostaglandin production. Compounds that inhibit 5-lipoxygenase usually do so because they are antioxidants. However, the action of the boswellic acids does not rely on antioxidant properties and for these reasons it is described as novel and specific.^34,35 It was concluded that Boswellia could be a useful treatment in leukotriene-mediated inflammation and hypersensitivity-based disorders. Some degradation products of boswellic acids are also potent inhibitors of 5-lipoxygenase.³⁶

There is a suggestion from in vitro research that the action of Boswellia on 5-lipoxygenase is biphasic.³⁷ Concentrations greater than 10 to 15 µg/mL inhibited the enzyme in stimulated neutrophils, as noted previously. In contrast, lower concentrations of extracts (1 to 10 µg/mL) potentiated 5-lipoxygenase product formation. It was proposed in one study that this stimulatory effect on 5-lipoxygenase activity may be due (at least in part) to 3-oxo-tirucallic acid and related compounds, rather than the boswellic acids.^38,39

A 2009 study found that while the 11-keto-boswellic acids efficiently suppressed 5-lipoxygenase activity in isolated neutrophils, this effect was absent in whole human blood.⁴⁰ A single dose (800 mg) of Boswellia extract to 12 healthy male volunteers failed to suppress leukotriene B4 (a product of 5-lipoxygenase) in plasma. The authors suggested that, since leukotrienes do not play a major role in osteoarthritis and inflammatory bowel disease, a lack of clinical activity on 5-lipoxygenase is actually consistent with the observed value of Boswellia for these disorders. Their findings certainly question the relevance of 5-lipoxygenase inhibition to the pharmacological activity of Boswellia. However, unpublished results quoted in a recent review claimed inhibition of cysteine-leukotriene formation in stimulated granulocytes ex vivo from healthy humans given 1200 mg of a commercial Boswellia extract.¹¹ The inhibitory effect was more than 90% with a maximum 6 h after intake, which corresponds with the known pharmacokinetics of boswellic acids.

That the anti-inflammatory mechanism of Boswellia is not confined to the inhibition of leukotriene formation was highlighted in a 2006 review.⁴¹ There is suggestion from in vitro studies that Boswellia can alter the production of pro-inflammatory cytokines. AKBA and acetyl-alpha-boswellic acid downregulated tumour necrosis factor alpha (TNF-alpha) in stimulated peripheral monocytes by inhibiting NF-kappaB signalling.⁴² A related species (Boswellia carterii) inhibited Th1 cytokines and promoted Th2 cytokines in vitro.⁴³ One mechanism by which TNF-alpha causes inflammation is by potently inducing the expression of adhesion molecules such as VCAM-1 (vascular cell adhesion molecule 1). This was completely prevented by Boswellia extract in vitro for isolated human microvascular endothelial cells.⁴⁴

Boswellic acids were also found to inhibit another pro-inflammatory enzyme in vitro: human leukocyte elastase (HLE). The dual inhibition of both 5-lipoxygenase and HLE is apparently unique to these compounds.⁴⁵ They also possess anticomplementary activity in the classical and alternative complement pathways. A key enzyme of the classical complement pathway (C3-convertase) was inhibited.^46,47 (Complement is a blood-based enzymatic cascade that serves to amplify, or complement, other inflammatory processes in the body. It is particularly implicated in the inflammation that occurs in rheumatoid arthritis.)

Like HLE, cathepsin G (catG) is another serine protease found in neutrophil granules that may participate in the breakdown of ingested pathogens and other inflammatory responses. CatG inhibitors have potential in the treatment of inflammatory conditions such as asthma, emphysema, psoriasis and rheumatoid arthritis.¹⁰ Boswellic acids exhibited a high and specific binding affinity for catG in vitro and potently suppressed the proteolytic activity of catG in a competitive and reversible manner.⁴⁸ Related serine proteases were significantly less sensitive in vitro, including HLE, or not affected at all. Boswellic acids inhibited chemoinvasion but not chemotaxis of challenged neutrophils in vitro and suppressed catG induced calcium mobilisation in human platelets in vitro. Oral administration of a defined Boswellia extract to 12 healthy volunteers (800 mg single dose) and to five patients with Crohn’s disease (2400 mg/day) significantly lowered the catG activity of various blood samples.¹¹ This research represents an intriguing development in the understanding of the anti-inflammatory activity of Boswellia.

Anti-allergic activity

An extract of Boswellia containing 60% AKBA was evaluated for anti-allergic and mast cell stabilising activity using passive rat paw anaphylaxis and induced degranulation of mast cells as the experimental in vivo models.⁴⁹ The extract inhibited the anaphylaxis reaction in a dose-dependent manner at oral doses of 20, 40 and 80 mg/kg, but was not as strong as dexamethasone (0.27 mg/kg). Similarly, a dose-dependent inhibition of mast cell degranulation was observed at the above doses.

Anticancer activity

Boswellia extract and boswellic acids have shown anticancer activities in cell cultures, including inhibition of cell growth and DNA synthesis.^50,51 The induction of differentiation and apoptosis (possibly due to topoisomerase I inhibition) suggests that boswellic acids may be useful in the treatment of leukaemia.^52–54

The ability of boswellic acids (such as boswellic acid acetate and AKBA) to induce in vitro apoptosis has been demonstrated in the following tumour cell lines: myeloid leukaemia cells,⁵⁵ metastatic melanoma and fibrosarcoma cells,⁵⁶ various leukaemia, haematological and brain tumour cell lines,⁵⁷ colon cancer cells,⁵⁸ liver cancer Hep G2 cells⁵⁹ and malignant glioma.⁶⁰ In addition AKBA was found to be cytotoxic towards meningioma cells in vitro.^61,62 A useful and extensive review of the anticancer activity of the boswellic acids is available,⁶³ as is a discussion of their molecular targets in this context.⁶⁴

Topical application of Boswellia extract with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibited the expected formation of skin tumours in mice.^65,66 Boswellic acids have also been shown to inhibit tumour growth in vivo using a rat brain tumour model (glioma), albeit at quite high doses (720 mg/kg boswellic acids).⁶⁷ The effect was dose dependent. In mice carrying prostate cancer cell tumours, systemic doses of AKBA inhibited tumour growth and triggered apoptosis in the absence of systemic toxicity.⁶⁸

Other activity

Boswellia resin demonstrated lipid lowering activity in vivo.^69–71 It is interesting that another Ayurvedic remedy, the resin from a plant in the same family, Commiphora mukul, has demonstrated hypocholesterolaemic activity both in vivo and in clinical trials, although a recent trial has cast doubt on its clinical efficacy.⁷²

Oral doses of AKBA (100 mg/kg) and nimesulide (2.42 mg/kg) for 15 days significantly reversed the age-induced deterioration of memory, cognitive performance and meta-function in mice.⁷³

The 11-methylene analogue of 11-keto-boswellic acid (KBA), namely beta-boswellic acid, potently induced calcium mobilisation in platelets in vitro.⁷⁴ Pivotal protein kinases were activated, resulting in functional platelet responses such as thrombin generation, liberation of arachidonic acid and aggregation.

Arthritis

A significant improvement in symptoms was observed for 60 rheumatoid arthritis (RA) patients after receiving 6 to 8 weeks of treatment with boswellic acids in an open label study.⁸² After reviewing the successful results of preclinical toxicology and efficacy studies, an uncontrolled clinical trial was undertaken at the orthopaedic department of Government Medical College, Jammu, India.^83,84 Results for 175 RA patients were ‘excellent’ for 14% and ‘good’ for 44%. Most patients taking Boswellia had some improvement in symptoms such as pain, stiffness and poor grip strength. Improvement occurred after 2 to 4 weeks of treatment.

In another uncontrolled study, Boswellia extract was given to 30 patients with RA.⁸⁵ The percentage of patients with detectable C-reactive protein was 63% initially, but this decreased to 47% after 6 months of treatment, a significant finding. This suggests that Boswellia may have a disease-modifying effect in RA.

The clinical efficacy of a herbomineral formulation containing Withania somnifera, Boswellia serrata, Curcuma longa (turmeric) and a zinc complex was evaluated in a randomised, double blind, placebo-controlled, crossover study in 42 patients with osteoarthritis.⁸⁶ The treatment period was 3 months, with a 15-day washout period before crossover and then another 3 months of treatment. Clinical efficacy was evaluated every fortnight on the basis of such findings as severity of pain, morning stiffness, joint score, disability score and grip strength. Treatment with the herbomineral formulation produced a significant drop in pain (p<0.001) and disability (p<0.05). However, X-ray assessment of joints did not show any significant changes.

The above herbomineral formulation was also evaluated in a randomised, double blind, placebo-controlled, cross-over trial of 20 RA patients for a period of 3 months. Significantly greater relief of pain, decreased morning stiffness, Ritchie Articular Index, joint score and erythrocyte sedimentation rate (ESR) were observed for those treated with the product. Seroconversion occurred for most of the treated patients, but radiological assessment did not show significant changes in either group.⁸⁷

Etzel in 1996 reviewed 12 controlled clinical trials conducted in Germany or India (including those cited above) that assessed the effects of Boswellia in the treatment of RA.⁸⁸ Of these studies, only two were double blind, placebo-controlled trials, so results were difficult to interpret overall. However, summarising the results of different studies, Etzel suggested the following:

These positive outcomes contrast with a subsequent German study that found, under double blind, placebo-controlled conditions, that Boswellia was not more effective than placebo in patients with chronic polyarthritis (presumably mainly RA).⁸⁹ The authors of this study reserved their judgement, suggesting that a larger trial than the one they conducted was necessary to confirm or reject the use of Boswellia in RA sufferers, especially since the dropout rate in their trial was quite high.

An extract of Boswellia standardised to 40% boswellic acids by HPLC (high-performance liquid chromatography) yielded good results in the treatment of osteoarthritis.⁹⁰ A randomised, double blind, placebo-controlled, crossover study was conducted to assess the efficacy, safety and tolerability of the Boswellia extract (1000 mg/day) in 30 patients with osteoarthritis of the knee, 15 each receiving active treatment or placebo for 8 weeks. After the first intervention, washout was given and then the groups were crossed over to receive the opposite intervention for 8 weeks. All patients receiving herbal treatment reported a significant decrease in knee pain, increased knee flexion and increased walking distance. The frequency of swelling in the knee joint was substantially decreased, but radiologically there was no change. Boswellia was well tolerated by the patients, except for minor gastrointestinal adverse reactions.

Since the boswellic acids were considered to be specific, non-redox inhibitors of 5-lipoxygenase and hence leukotriene biosynthesis, research attention as noted above had previously focused on the effects of Boswellia in inflammatory joint diseases such as RA. Despite this research focus on RA, herbal clinicians also favoured the use of Boswellia in osteoarthritis. The results of the above trial provided the first good evidence to support this application. What was striking about the trial was the substantial clinical benefit observed. Results were highly statistically significant (p<0.001) and changes in treatment parameters were quite large. For example, in the first 8-week treatment period before crossover, the pain index in the Boswellia group fell from 2.7±0.45 to 0.26±0.45, the loss of movement index was reduced from 2.8±0.41 to 0.30±0.48 and the swelling index went from 1.1±0.91 to zero. The group receiving the placebo treatment after crossover showed substantial deterioration over the ensuing 8 weeks, suggesting that the 21-day washout period before crossover was insufficient. Although this is a flaw in the experimental design, it suggests a substantial residual therapeutic benefit after stopping Boswellia.

A prospective, randomised study conducted in India assessed the efficacy and tolerability of Boswellia extract in comparison to valdecoxib, a selective COX-2 inhibitor.⁹¹ Sixty-six patients aged between 40 and 70 years with primary osteoarthritis of the knee, diagnosed according to the criteria of the American College of Rheumatology, were recruited. X-rays confirmed the diagnosis. Patients were assessed by the WOMAC scale at baseline and at monthly intervals until 1 month after discontinuation of 6 months’ therapy. The WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scale consists of questions based on the three symptoms (pain, stiffness and difficulty in performing daily activities), to which the patient assigns a number between 0 and 100. Patients received either 1000 mg standardised Boswellia extract (containing 40% boswellic acids, which corresponded to a dose of 400 mg/day of boswellic acids) or valdecoxib 10 mg/day. There were 33 patients in each treatment group. During the trial patients were permitted to continue receiving physiotherapy and take a rescue medication (ibuprofen).

Results indicated that Boswellia extract was as effective as valdecoxib for knee osteoarthritis. In comparison with valdecoxib, Boswellia had a slower onset of action but the effect persisted after the discontinuation of therapy (unlike valdecoxib). The implications of this trial are that Boswellia is effective for knee osteoarthritis but needs to be taken for at least 2 months to establish the full clinical effect. Furthermore, the slow onset and slow washout of benefit suggests it could be disease modifying.

In a trial published in 2008, 75 patients with knee osteoarthritis received either Boswellia extract (containing 100 or 250 mg/day of an AKBA-enriched selective boswellic acid extract) or placebo for 90 days. Boswellia conferred a clinically and statistically significant dose-response improvement in pain and physical function scores. Symptom alleviation was faster in the higher dose Boswellia group (as early as 7 days) and a significant reduction in synovial fluid levels of matrix metalloproteinase-3 (a cartilage-degrading enzyme) was also observed for the Boswellia groups.⁹²

A later study evaluated the activity of this AKBA-enriched selective boswellic acid extract at 100 mg/day against a similar extract with enhanced bioavailability (also at 100 mg/day) and a placebo in 60 patients with knee osteoarthritis.⁹³ A double blind, randomised, placebo-controlled design was used, with a trial period of 90 days. At the end of the study, both Boswellia extracts conferred clinically and statistically significant improvements in pain and physical function scores versus placebo (various p values). Significant improvements were recorded as early as 7 days for the enhanced bioavailability extract, which demonstrated better activity than the other extract. By 90 days, some clinical changes for the enhanced bioavailability extract were particularly marked. For example, the WOMAC pain subscale fell by 69% (p<0.0001 versus placebo) and the WOMAC stiffness subscale by 70.1% (p<0.0001 versus placebo) from baseline.

A formulation containing Withania, Boswellia, turmeric and ginger was shown to be effective in osteoarthritis in a double blind, randomised, placebo-controlled trial involving 99 patients.⁹⁴ Concurrent NSAIDs or analgesics were not permitted. Significant improvements were noted for pain (visual analogue scale) (p<0.05) and a modified WOMAC score (p<0.01) by the end of trial (32 weeks). There was no significant difference in type and number of adverse effects between active and placebo, although 28 patients did not complete the trial.

Ulcerative colitis

A group of Indian and German scientists conducted an open, non-randomised pilot study to test the hypothesis that Boswellia might be beneficial for the treatment of ulcerative colitis. For the study, 34 patients (18 with grade II and 16 with grade III colitis) were given 350 mg of Boswellia resin three times a day, and eight patients (five with grade II and three with grade III colitis) were given the drug sulfasalazine, 1 g three times a day. The authors commented that the cost of the drug was responsible for the small control group. Symptoms such as abdominal pain, loose stool, mucus and blood improved in both groups, with results for the control sulfasalazine group slightly better than the Boswellia group. Sigmoidoscopic examination for the grading of the disease and rectal biopsies both showed substantial improvements in the two treatment groups, and there was no statistically significant difference between them. About 80% of the patients receiving Boswellia went into remission. The authors concluded that, although they could not statistically confirm the superiority of Boswellia over sulfasalazine, the data suggest that it is at least not inferior.⁹⁵

Twenty patients with chronic colitis received Boswellia gum resin (900 mg/day for 6 weeks) and another 10 patients were given sulfasalazine (3 g/day for 6 weeks) in an open label trial.⁹⁶ Out of 20 patients treated with Boswellia, 18 went into remission (90% compared with 60% for sulfasalazine).

Asthma

In a double blind, placebo-controlled clinical study, 80 patients with chronic asthma were treated with 900 mg/day of Boswellia, gum resin or placebo for 6 weeks.⁹⁷ Only 27% of patients in the control group showed improvement, whereas 70% of patients taking Boswellia improved. After taking Boswellia, positive changes were observed for shortness of breath, number of attacks and respiratory capacity as well as indicators of inflammation. Comparing the Boswellia group with the placebo group, there was a significant improvement in forced expiratory volume (in 1 second), a measure of bronchial obstruction (p=0.0001). Peak expiratory flow rate, a measure of lung capacity, was also significantly increased (p=0.0001). The number of asthma attacks was lower in the Boswellia group (p=0.0001). Additionally, Boswellia treatment showed substantial improvements (compared with placebo) in secondary outcome parameters such as rhonchi, eosinophil count, ESR and respiratory rate (p<0.05). Two patients who received Boswellia complained of epigastric pain and nausea.

It should not be assumed that inhibition of leukotrienes is the only mechanism by which Boswellia might provide beneficial effects for asthma, especially given the antiallergic activity from experimental models.

Crohn’s disease

The safety and efficacy of a Boswellia extract was compared against mesalazine for the treatment of 102 patients with active Crohn’s disease in an 8-week randomised, double blind European study.⁹⁸ The primary clinical outcome measured was the change in Crohn’s Disease Activity Index (CDAI). After therapy with Boswellia extract (3.6 g/day) the average CDAI was reduced by 90, compared with a reduction of 53 for the mesalazine group (4.5 g/day). The authors concluded that the Boswellia extract was as effective as mesalazine, which is the current anti-inflammatory treatment for this disorder. Considering the observed fewer side effects and better safety profile of Boswellia, they suggested that this novel herbal treatment appears to be superior to mesalazine in terms of a risk-benefit evaluation.

In contrast, a 52-week double blind, placebo-controlled randomised trial in 108 patients with Crohn’s disease found 2400 mg/day of a Boswellia extract was not superior to placebo in terms of maintaining remission.⁹⁹ However, only 66 patients completed the trial due to early termination and the extract did not seem to deliver high plasma levels of boswellic acids relative to other studies (see under Pharmacokinetics).¹¹ Boswellia treatment was well tolerated.

Brain tumours

Malignant brain tumours produce highly active forms of leukotrienes and this causes localised fluid build-up in the brain around the tumour, which damages healthy nerve cells. Twelve patients with malignant glioma, a type of brain tumour, were given 3600 mg/day of Boswellia extract (standardised to 60% boswellic acids) for 7 days prior to surgery.¹⁰⁰ Ten patients showed a decrease in fluid around the tumour, with an average reduction of 30% in eight of the 12 patients. Signs of brain damage decreased during the treatment; one patient became worse. Vomiting as a side effect was observed in one patient. This resulted in the European Commission declaring Boswellia as an orphan drug (a drug with no sponsors to fund the registration process) for the treatment of oedema resulting from brain tumours.⁷⁵

Nineteen children and adolescents with intracranial tumours received palliative therapy with Boswellia extract at a maximum dose of 126 mg/kg/day for up to 26 months.¹⁰¹ All patients were previously treated with conventional therapy. An anti-oedematous effect was demonstrated by MRI in one patient. Five of the 19 children reported an improvement of general health (perhaps a placebo effect). Some objective improvement, sometimes transient, was observed in seven patients.

Twelve patients with brain tumours and progressive oedema caused by either the tumour or treatment were given 3600 mg/day Boswellia extract for 4 weeks.¹⁰² Oedema was reduced in five patients. Of five patients with treatment-related leukoencephalopathy, the clinical improvement following Boswellia was sustained for several months.

Forty-four patients with primary or secondary malignant cerebral tumours were randomly assigned to radiotherapy plus either 4200 mg/day Boswellia extract or placebo in a double blind trial.¹⁰³ Compared with baseline and measured immediately after the end of radiotherapy, a greater than 75% reduction in cerebral oedema was observed in 60% of the patients receiving Boswellia versus 26% receiving placebo (p=0.023). The dexamethasone dose during radiotherapy did not significantly differ between groups. The tumour/oedema volume ratio decreased only in the Boswellia group, suggesting an antitumour effect in addition to the anti-oedema activity. However, progression-free survival did not differ between the groups. Nonetheless, the better tumour response to radiotherapy was an unexpected finding. Common adverse events associated with radiotherapy were similar in both groups, although gastrointestinal discomfort was probably higher in the Boswellia group. While boswellic acids could be detected in patients’ serum, the level of AKBA was quite low and could not be detected. Compliance with the high dose of extract used was an issue.

Other conditions

Collagenous colitis is a form of microscopic colitis of unknown aetiology and pathogenesis. The main symptom is chronic watery diarrhoea with few or no endoscopic abnormalities. Patients (n=31) with proven collagenous colitis were randomised to receive either 400 mg of Boswellia extract three times daily or placebo for 6 weeks in a double blind, randomised placebo-controlled trial.¹⁰⁴ Clinical remission at the end of the trial was higher in the Boswellia group (64% versus 26% for protocol, p=0.04; 44% versus 27% intention-to-treat, p=0.25). The authors concluded that results were promising and larger trials are necessary to confirm any benefit from Boswellia for this disorder.

A multicentre veterinary clinical trial was conducted by 10 practising veterinarians in Switzerland involving 29 dogs with degenerative chronic joint and spinal osteoarthritis.¹⁰⁵ An extract of Boswellia was administered in food at a dose of 400 mg/10 kg/day over 6 weeks. A statistically significant reduction in signs such as intermittent lameness and stiff gait were reported after 6 weeks. In five dogs reversible brief episodes of diarrhoea and flatulence occurred, but only in one case was a relationship to the Boswellia treatment suspected.

Antimicrobial activity

An early in vitro study demonstrated some activity for the alcoholic extract of buchu against microflora typical of urinary tract infections.¹⁵ However, only the essential oil showed considerable activity against all the test organisms.

More recently poor or absent antimicrobial activity was observed for buchu essential oil against five different microorganisms using the zone of inhibition technique.¹⁶ This finding was somewhat supported by a later study that found only moderate activity, with minimum inhibitory concentrations (MIC) for the oil varying from 4 to 32 mg/mL (depending on the microorganism tested for Bacillus cereus, Staphylococcus aureus, Klebsiella pneumoniae and Candida albicans), as determined by a microtitre plate dilution method.¹⁷ In fact, the methanol:dichloromethane (1:1) extract of buchu leaf was more active than its hydrodistilled essential oil in this test model (MIC range against the same organisms 2 to 4 mg/mL).¹⁸

In an attempt to better reflect in vivo activity, extracts of buchu were treated with simulated gastric and intestinal fluids. The water extract showed a doubling of antimicrobial activity after it was subjected to simulated intestinal conditions. Intestinal transport simulation using the Caco-2 cell monolayer revealed good bioavailability for the compounds present in this extract.^19,20

Other activity

At a high concentration buchu essential oil had an initial spasmogenic action on isolated guinea pig ileum, followed by spasmolysis. Cyclic AMP generation and the blocking of calcium channels were suggested as possible mechanisms for the spasmolytic activity, based on the experimental probes used.¹⁶

A relatively strong inhibition of 5-lipoxygenase was observed in vitro for the essential oil (IC₅₀=50.4 μg/mL), but not the methanol:dichloromethane (1:1) extract.^17,20

Antithyroid and antigonadotropic activities

It is probably most useful to review the pharmacological research into the antihormonal activity of Lycopus in an approximate chronological order, as there is certainly an aspect of unfolding discovery to the story.

Madaus, Cook and Albus in 1941 were able to show in experimental investigations that the effects of L. europaeus and L. virginicus L. were similar.¹¹ Lycopus countered the typical weight decrease and tachycardia from thyroxine in the rabbit in an acute model. Results from another model also suggested a direct thyroxine antagonism: thyroxine antagonises the temperature fall induced by novocaine injection in the guinea pig and this effect was cancelled by Lycopus administration. Thyroxine causes an increased oxygen requirement as a result of increased metabolism and Lycopus countered this effect in rats. Next to this direct antithyroxine effect, the authors also showed effects on TSH activity. After repeated injection of TSH, oxygen consumption in the guinea pig increased by around 25%. Simultaneous administration of Lycopus extract reduced this to about 10%, but only at the highest dosage.¹²

Pharmacodynamic research on Lycopus began in earnest in the early 1960s when Kemper and co-workers found that an aqueous extract of L. virginicus inhibited the actions of gonadotropic hormones and TSH in vivo (based on organ weights) after administration by injection to guinea pigs and rats.^13,14 However, a preparation of L. europaeus had no influence on thyroid metabolism in rats after oral doses, as assessed using radioactive iodine.¹⁵

A paper published in 1970 claimed, on the basis of in vivo experiments using doses administered by injection, that an oxidised form of lithospermic acid was the antigonadotropic principle in L. virginicus.¹⁶ However, it was the work of the late Dr Hilke Winterhoff and team that found a different basis for this and the antithyroid activity in a series of studies published from 1976 to recently. Lithospermic acid was shown to have little antihormonal activity compared to the freeze-dried extract of Lycopus.^17,18 This freeze-dried aqueous extract of Lycopus (species not specified) given alone by injection or with TSH to infant female rats led to a marked fall in circulating thyroid hormones.¹⁹ When TRH and L. virginicus extract were co-administered (at different sites) by injection to rats, TSH levels were significantly lower after 10 minutes when compared to the TRH and saline controls.²⁰ As a result, thyroid hormone levels were suppressed and significantly lower 3 h later. Pretreatment of rats with dried extract for 4 days resulted in a drop in peripheral thyroid hormone levels.²⁰

In the euthyroid rat, injections (50 mg/kg) of freeze-dried extracts of both L. europaeus and L. virginicus greatly reduced serum and pituitary TSH levels.²¹ Effects were less clear in hypothyroid rats. Serum prolactin was also reduced by L. virginicus injection, but only at 400 mg/kg. L. europaeus injection (50 mg/kg) did significantly lower pituitary (but not serum) prolactin levels.

The active components suggested by Winterhoff and team as responsible for these effects were the oxidation products of phenolic compounds such as rosmarinic acid, which are abundant in Lycopus species.²² These showed marked antigonadotropic activity in a rat model after injection. This line of research was further progressed by this group in collaboration with others, including several in vitro investigations conducted in the 1980s. The antigonadotropic activity of ether-extracted fractions of L. virginicus aqueous extracts was tested in a suitable model (details not specified).²³ Within the ether extracts, significant activity was only found after the addition of an oxidising agent (up to a 10-fold increase). This oxidised and active form was identified to contain oxidation products of rosmarinic acid. Freeze-dried aqueous extracts of L. virginicus and L. europaeus inhibited the binding of bovine TSH to human thyroid plasma membranes and inhibited the stimulation of adenylate cyclase.²⁴ Auto-oxidation products of the 3,4-dihydroxycinnamic acid derivatives (such as caffeic, rosmarinic, chlorogenic and ellagic acids) were also active in the same model.²⁵ It was suggested that these compounds form adducts with TSH, resulting in a greatly reduced or absent ability to bind to the TSH receptor.²⁶ In later research, rosmarinic acid and a freeze-dried aqueous extract of L. virginicus also inhibited forskolin-induced activation of adenylate cyclase in cultured rat thyroid cells.²⁷

The impact of Lycopus on the peripheral conversion of T4 to T3 was investigated in vitro using iodothyronine deiodinases from rat liver microsomes.²⁸ Preparations of L. virginicus, especially the ether fraction of hot aqueous extracts, markedly inhibited the enzyme in a dose-dependent manner. Subsequent investigation found that the active principles exhibited chemical characteristics of phenolcarboxylic acids (e.g. rosmarinic acid). Curiously, oxidation of extracts with potassium permanganate decreased this activity.²⁹

In all samples of Graves’ immunoglobulin G (IgG) tested, incubation with L. virginicus or L. europaeus or their auto-oxidised constituents decreased the TSH-binding inhibitor activity in vitro. This was in a dose-dependent manner and with some degree of specificity.³⁰ The plant extracts and their auto-oxidised constituents also inhibited the biological responses to Graves’ IgG in vitro.

The efficacy of injections of L. virginicus extracts for up to 3 days at inhibiting thyroid hormone levels and thyroid weight varied with the method of preparation.³¹ Extraction with boiling water or ethanol yielded inactive extracts, whereas oxidation with potassium permanganate re-established activity. The reduction in prolactin levels observed in an earlier study was also confirmed (as assessed by assay 6 h after a single intravenous injection). It was shown in a subsequent study that several phenolic plant ingredients mentioned already, but additionally luteolin-7-beta-glucuronide,³² confer antigonadotropic activity. However, their oxidation products are likely to be more active.³³ The suggestion that L. europaeus contains lithospermic acid was also refuted. Oligomeric (short polymers) oxidation products of caffeic acid (cyclolignan derivatives) with antigonadotropic activity were subsequently identified as likely active components.^34,35

As well as the previously noted antagonism of TSH, results from a series of experiments suggested that injections of L. europaeus are capable of suppressing thyroid hormone secretion by a direct intrathyroidal attack.³⁶ Additional phenolic acids (including isoferulic acid and ferulic acid) as well as caffeic acid were active in this TSH-antagonism model.

One reservation that can be expressed about the above research is that most of the results have been generated using in vitro models or in vivo models following injection of the herbal extracts or relevant compounds. This was addressed by Winterhoff’s team in a 1994 publication where a 70% ethanolic extract L. europaeus was administered by oral means to rats, albeit at quite high doses of 200 and/or 1000 mg/kg.³⁷ Diverse endocrine parameters were measured between 3 and 24 h after oral doses and compared with intraperitoneal doses (of L. virginicus). Oral application of the extract caused a long-lasting decrease in T3 levels, presumably due to reduced peripheral T4 deiodination. A pronounced reduction of T4 and TSH was observed, as well as LH (luteinising hormone), indicating a central action for the extract.

The impact of oral L. europaeus (2×5 mg or 2×200 mg/kg per day for up to 8 weeks of a dried aqueous-ethanolic extract) on cardiac symptoms in hyperthyroid rats was compared with the beta-blocking drug atenolol.³⁸ Even the lower dose of the herb countered the raised body temperature, whereas the reduced body weight and increased food intake was not influenced by any treatment. No significant changes in thyroid hormone levels or TSH were observed. Lycopus (in general both doses) and atenolol reduced the increased heart rate, blood pressure and heart size, but the drug was considerably more active with respect to heart rate. Interestingly, Lycopus given to normal rats at 2×200 mg/kg per day had no impact on any of the above parameters. Collectively the above findings suggest that the herb only antagonises the effects of increased thyroid hormone levels, and does this without altering depressed TSH and elevated thyroxine levels, at least in the model used.

This work was subsequently extended in two publications using three rat models of differing severity of hyperthyroidism induced by differing applications of T4. Findings were similar to the above study in both publications, with Lycopus extract, extract fractions and powdered herb having almost the same potency as beta-blockers (atenolol and propranolol) in reducing body temperature.^39,40 The effects on beta-adrenoreceptor density, blood pressure and heart rate were less distinct, but still significant. In the later publication there was some suggestion that Lycopus powder had inhibited T4 to T3 conversion.⁴⁰ (Note that this result may have been more determined by the model used than the form of Lycopus, since the powder was only tested in one model of hyperthyroidism.)

Summarising the research to date, results from in vitro experiments or in vivo models with dosage by injection suggest that Lycopus extracts or its components at relatively high doses antagonised or reduced pituitary hormones (TSH, gonadotropins, prolactin), reduced thyroxine production, reduced peripheral conversion of T4 to T3 and antagonised the binding and effects of Graves’ IgG. In terms of phytochemical components responsible for these effects, oligomeric oxidation products of phenolic acids such as caffeic acid were found to be most active. As a consequence, freshly prepared aqueous-ethanolic extracts were not found to be active, as they are devoid of such products. However, some of the above results (TSH, T4 and T3 reductions) were confirmed in an oral-dose model using high doses of a commercial aqueous-ethanolic extract. Perhaps this extract was active because phenolic acid oxidation products had formed in the time since its manufacture. More recently, animal models using realistic oral doses of a commercial aqueous-ethanolic extract have provided quite a different perspective. Here it was found that Lycopus could antagonise the cardiac effects of induced hyperthyroidism without any corresponding change in thyroid hormones or TSH. Lycopus given orally to normal rats at such doses had no impact on thyroid function. The phytochemical components responsible for the activities observed in these later experiments have not been explored to date.

Other activity

A methanolic extract of L. europaeus was one of the three most active of 122 traditional Chinese herbs screened for in vitro activity against xanthine oxidase (the enzyme that catalyses purine metabolites to uric acid) with an IC₅₀ of 26 μg/mL.⁴¹ Two new isopimarane diterpenes were isolated from L. europaeus that were capable of potentiating the in vitro activities of tetracycline and erythromycin against resistant strains of Staphylococcus aureus possessing multidrug efflux mechanisms.⁴² Aqueous and methanolic extracts of L. europaeus showed high radical scavenger capacity compared to 17 other medicinal Labiatae species tested.⁴³