Herbs & Supplements:
Black Cohosh
Cimicifuga racemosa
Principal Proposed Uses
•
Menopausal Symptoms
Other Proposed Uses
•
High Cholesterol, Osteoporosis, PMS, Dysmenorrhea (Painful Menstruation)
Black cohosh is a tall perennial herb originally found in the northeastern United States. Native Americans used it primarily for women's health problems, but also as a treatment for arthritis, fatigue, and snakebite. European colonists rapidly adopted the herb for similar uses, and in the late nineteenth century, black cohosh was the principal ingredient in the wildly popular Lydia E. Pinkham's Vegetable Compound for menstrual cramps. Migrating across the Atlantic, black cohosh became a popular European treatment for women's problems, arthritis, and high blood pressure.
What Is Black Cohosh Used for Today?
Black cohosh has been approved by Germany's Commission E for use in treating menopause, dysmenorrhea, and PMS. However, only the first of these uses has any supporting evidence, and it is far from convincing.
One study suggests that black cohosh might improve the cholesterol profile in postmenopausal women; the same study provides very weak evidence that black cohosh might help prevent osteoporosis.
In one study, black cohosh did not prove effective for reducing the hot flashes often experienced by women who have undergone treatment for breast cancer.
What Is the Scientific Evidence for Black Cohosh?
Menopausal Symptoms
Only two double-blind, placebo-controlled trials of black cohosh for menopausal symptoms have been reported.
The first study produced results that are difficult to trust. This trial followed 80 women for 12 weeks, and compared the effects of black cohosh, conjugated estrogens (0.625 mg), and placebo.1 The results indicated that black cohosh produced significantly greater improvements in menopausal symptoms than placebo. However, estrogen proved no better than placebo—a result so surprising that it casts serious doubt on the meaningfulness of the results. Furthermore, black cohosh was found to produce estrogen-like changes in the genital tract; as described below, it is now believed that black cohosh does not have any such actions.
At the time of this trial, black cohosh was thought to be a phytoestrogen—a plant that influences the body in a manner similar to estrogen. However, subsequent research has shown that black cohosh does not have typical phytoestrogenic effects. For example, a well-designed, double-blind study that compared two different dosages of black cohosh did not find any change in vaginal-cell appearance, or any other objective measurements that would indicate an estrogen-like effect.2 Test tube and animal studies, as well as preliminary human trials, have also failed to find that black cohosh is a phytoestrogen.3,21-24
More recently, some evidence suggests that black cohosh might have selective estrogenic effects, meaning that it could act on certain tissues (such as bone) and not others (such as the uterus).11-13,25 However, the evidence for such an effect is still weak, and in any case, the consensus remains that black cohosh does not have estrogen-like effects on cells of either the uterus or vagina.
Thus, something appears to have gone seriously wrong in the double-blind trial described above. Some experts in the field have even speculated that researchers conducting the first trial mixed up the black cohosh and estrogen groups, or skewed the results in some other way.
If this study is dismissed, only one double-blind, placebo-controlled trial supporting the use of estrogen remains, one published so far only in abstract form. 25 This trial enrolled 97 postmenopausal women who complained of having more than three hot flashes daily. Participants were divided into the same three groups as in the first study.
The results showed that both estrogen and black cohosh improved menopausal symptoms to a greater extent than did placebo. However, while use of estrogen caused thickening of the wall of the uterus, black cohosh did not do so.
This is consistent with current thinking that black cohosh is not a phytoestrogen.
This latter study is the only meaningful evidence supporting the use of black cohosh for menopausal symptoms. Several other studies are also often cited as evidence, but in reality they prove nothing at all. 5–9 In these trials, all participants received black cohosh; there was no placebo group. Although women reported improvements in symptoms, there is no way to know that black cohosh was responsible. Women given placebo reliably report improvements in menopausal symptoms too; a 50% reduction in hot flashes is fairly typical.10 Thus, it is possible that the benefits seen in these uncontrolled studies had nothing to do with black cohosh.
Putting all this information together, it is fair to say that at present there is only scant supporting evidence for the use of black cohosh in menopausal symptoms.
Breast Cancer Survivors
Women who have had breast cancer frequently experience annoying hot flashes, for reasons that are not altogether clear. Estrogen treatment is not an option, as it might increase risk of cancer recurrence. However, based on increasing certainty that black cohosh is not estrogenic, researchers tested it to see if it would reduce hot flashes in 85 women who had undergone treatment for breast cancer. The results were not encouraging: in this 2-month, double-blind, placebo-controlled trial, black cohosh did not reduce overall hot-flash symptoms.4
Cholesterol
The most recent double-blind study of black cohosh for menopausal symptoms also found that black cohosh improved cholesterol profiles as compared to placebo. 25 The extent of this effect was not stated in the currently available abstract.
Osteoporosis
Evidence from the same study hints that black cohosh might help build bone. In the black cohosh group, levels of of a substance called “bone-specific alkaline phosphatase” increased. This chemical generally rises when the body is making new bone; however, more direct evidence is needed before it is reasonable to conclude that black cohosh is useful for preventing or reversing osteoporosis.
Dosage
The standard dosage of black cohosh is 1 or 2 tablets twice a day of a standardized extract, manufactured to contain 1 mg of 27-deoxyacteine per tablet.
Make sure not to confuse black cohosh with blue cohosh (Caulophyllum thalictroides). Blue cohosh is potentially more dangerous since it contains chemicals that are toxic to the heart; one published case report documents profound heart failure in a child born to a mother who used blue cohosh to induce labor.14
Safety Issues
Black cohosh seldom produces any side effects other than occasional mild gastrointestinal distress. Studies in rats have found no significant toxicity when black cohosh was given at 90 times the therapeutic dosage for a period of 6 months.15 Since 6 months in a rat corresponds to decades in a human, this study appears to make a strong statement about the long-term safety of black cohosh.
Unlike estrogen, black cohosh does not stimulate breast-cancer cells growing in a test tube.16,17,18 However, black cohosh has not yet been subjected to large-scale studies similar to those conducted for estrogen. For this reason, safety for those with previous breast cancer is not known. Also, because of potential hormonal activity, black cohosh is not recommended for adolescents or pregnant or nursing women.
Black cohosh has been found to slightly lower blood pressure and blood sugar in certain animals.19,20 For this reason, it's possible that the herb could interact with drugs for high blood pressure or diabetes, but there are no reports of any such problems.
Safety in young children or those with severe liver or kidney disease is not known.
View References
Last reviewed September 2002 by Medical Review Board
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