Black cohosh's therapeutic uses

• PRINCIPAL PROPOSED USE: Menopausal symptoms
• OTHER PROPOSED USES: Dysmenorrhea (painful menstruation), osteoporosis, premenstrual syndrome

Overview

Black cohosh (Actaea racemosa, formerly Cimicifuga racemosa) 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 kidney disorders, arthritis, fatigue, sore throat, rheumatism, and snakebite. European colonists rapidly adopted the herb for similar uses. In the late nineteenth century, black cohosh was the principal ingredient in the wildly popular Lydia E. Pinkham’s Vegetable Compound for menstrual cramps.

Black cohosh’s main use today is for the treatment of menopausal symptoms. Meaningful but far from definitive evidence indicates that black cohosh extract might reduce hot flashes, night sweats, vaginal dryness, vertigo, sleep disturbances, and other symptoms of menopause.

Therapeutic Dosages

The most commonly used dosage of black cohosh is one or two 20-milligram (mg) tablets twice daily of a standardized extract, manufactured to contain one milligram of 27-deoxyactein per tablet. Other research indicates dosing may range from 40 to 128 mg per day.

Supplemental black cohosh is available as a powdered whole herb, liquid, and dried extracts in pill form. Usually, supplements provide one milligram of triterpene glycosides, like 27-deoxyactein or actein. To make tea from dried black cohosh, 20 grams of dried root in 34 ounces of water provides an appropriate dose. One should consume three cups daily.

An analysis of eleven available black cohosh products found that three of them contained an Asian herb related to black cohosh rather than the proper herb. Black cohosh should not be confused with the toxic herb blue cohosh (Caulophyllum thalictroides).

Therapeutic Uses

In the past, black cohosh was believed to be a phytoestrogen, a plant-based substance that has actions similar to estrogen. However, growing evidence indicates that black cohosh does not have general estrogen-like actions. Rather, it may act like estrogen only in certain areas of the body, such as the brain to reduce hot flashes, in bone to potentially fight osteoporosis, and in the vagina to reduce vaginal dryness.

Black cohosh has also been studied for reducing hot flashes in women who have undergone surgery for breast cancer, but it does not appear to be effective for this purpose. Black cohosh is sometimes recommended as a kind of general women’s herb said to be effective for a variety of menstrual issues, such as premenstrual syndrome (PMS), premenstrual dysphoric disorder (PMDD) or dysmenorrhea, and irregular menstruation. Other proposed uses include arthritis relief, uterine fibroids, cancer, and insomnia. However, no meaningful evidence supports the herb’s use for these conditions.

Scientific Evidence

Menopausal symptoms. The body of evidence regarding black cohosh for menopausal symptoms remains incomplete and inconsistent. The best study was a two-week, double-blind, placebo-controlled trial of 304 women with menopausal symptoms. This study appeared to find that black cohosh was more effective than placebo. The best evidence was for a reduction in hot flashes. However, the statistical procedures used in the study were somewhat unusual and open to question.

Promising results were also seen in a three-month, double-blind study of 120 menopausal women. Participants were given either black cohosh or fluoxetine (Prozac). During the trial, black cohosh proved more effective than fluoxetine for hot flashes, but fluoxetine was more effective for menopause-related mood changes.

Previous smaller studies have found improvements not only in hot flashes but also in other symptoms of menopause. For example, in a double-blind, placebo-controlled study, ninety-seven menopausal women received black cohosh, estrogen, or placebo for three months. The results indicated that the herb reduced overall menopausal symptoms, such as hot flashes, to the same extent as the drug. In addition, microscopic analysis showed that black cohosh had an estrogen-like effect on the cells of the vagina. This suggests that black cohosh might reduce vaginal thinning. However, black cohosh did not affect the cells of the uterus in an estrogen-like manner. This, too, is a positive result, as estrogen’s effects on the uterus are potentially harmful. Finally, the study found hints that black cohosh might help protect bone. However, many of the study participants dropped out, making the results less reliable.

One study, too small to have statistically reliable results, found black cohosh as effective as 0.6 mg daily of conjugated estrogens. A study reported in 2006 found that black cohosh has weak estrogen-like effects on vaginal cells and possible positive effects on bonespecifically, stimulating new bone formation.

An earlier study also found multiple benefits with black cohosh, but its results are unreliable. This trial followed eighty women for twelve weeks and compared the effects of 20 mg of black cohosh, estrogen, and placebo. Again, black cohosh improved menopausal symptoms and vaginal cell health. However, in this study, estrogen proved less effective than a placebo. This result is so difficult to believe that it casts serious doubt on the meaningfulness of the results.

Several other studies are also often cited as evidence that black cohosh is useful for various symptoms of menopause, but in reality, they prove nothing. These trials lacked a placebo group. Although women reported improvements in symptoms, there is no way to know whether black cohosh was responsible. Women given a placebo reliably report improvements in menopausal symptoms, too; a 50 percent reduction in hot flashes is fairly typical. Thus, it is possible that the observed benefits in these studies had nothing to do with black cohosh.

A substantial double-blind study published in 2007 with 244 participants compared black cohosh against the synthetic hormone tibolone and found them equally effective for treating menopausal symptoms. Though not approved as a drug in the United States, tibolone does appear to be effective for menopausal symptoms. Therefore, these results are somewhat promising. However, this study lacked a placebo group, and since the placebo effect is powerful for this condition, this omission significantly reduces the meaningfulness of the result.

One double-blind study evaluated a combination therapy containing black cohosh and St. John’s wort in 301 women with general menopausal symptoms as well as depression. The results showed that the use of the combination treatment was significantly more effective than a placebo for both problems. A smaller study using a combination of the same two herbs found improvements in overall menopausal symptoms as well as in cholesterol profile.

In contrast, several other studies failed to find any benefit. For example, in a twelve-month, double-blind, placebo-controlled study of 350 women, participants were given either black cohosh, a multibotanical containing ten herbs, the multibotanical plus soy, standard hormone replacement therapy, or placebo. The results showed that hormone replacement therapy was more effective than placebo, but the other treatments were not. In addition, a double-blind study of 122 women failed to find statistically significant benefits with black cohosh compared with placebo. Similar negative findings were reported in a study of 132 women, as well as one involving 124 women using a black cohosh/soy isoflavone combination. These negative outcomes were possibly due to the relatively small sizes of the black cohosh groups. In a condition like menopausal, where the placebo effect is strong, and when the treatment is relatively weak, large numbers of participants are necessary to prove benefit over the placebo effect. Nonetheless, this is an impressive number of negative studies, and some questions remain about the efficacy of this herb.

Black cohosh was long accepted as a phytoestrogen, a plant-based chemical with estrogen-like effects. However, subsequent evidence indicates that black cohosh is not a general phytoestrogen but may act like estrogen in only a few parts of the body. It does not appear to act like estrogen in the breast or uterus. If this theory is true, black cohosh is a selective-estrogen receptor modifier (SERM), somewhat like the drug raloxifen (Evista). However, more evidence is needed to establish this as fact.

Female infertility. Because of its estrogenic properties, researchers investigated whether black cohosh might be helpful in women who were having difficulty conceiving. Women with unexplained infertility who were not responding to clomiphene, a commonly used medication to induce ovulation, were randomly divided into two groups. Both groups continued to receive clomiphene, but the women in one of the groups also received 120 mg of black cohosh. Pregnancy rates were significantly higher in the black cohosh plus clomiphene group compared with the clomiphene-only group.

Breast cancer. Women who have had treatment for breast cancer frequently experience hot flashes, often but not always, because of the use of estrogen-antagonist medications like tamoxifen. Estrogen treatment is not an option for this problem, as it might increase the risk of cancer recurrence. Because black cohosh does not seem to have estrogen-like actions in the breast, researchers felt safe to try it in eighty-five women who had undergone treatment for breast cancer. The results were not encouraging: in this two-month, double-blind, placebo-controlled trial, black cohosh did not reduce hot-flash symptoms.

Arthritis. Some research indicates that black cohosh may help relieve arthritis pain, musculoskeletal pain, and osteoarthritis symptoms. One study found that black cohosh combined with several other herbs—willow bark, sarsaparilla, guaiacum resin, and poplar bark—helped relieve symptoms. However, because of the mix of herbs, it is difficult to confirm black cohosh's role in relieving these symptoms.

Safety Issues

Black cohosh seldom produces any side effects other than occasional mild gastrointestinal distress. One rigorous study did not find any possible deleterious effects on cholesterol levels, blood sugar, and blood coagulability. Studies in rats have found no significant toxicity when black cohosh was given at ninety times the therapeutic dosage for six months. Because six months of life in a rat corresponds to decades of life 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. However, black cohosh has not yet been subjected to large-scale studies like 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.

There are a growing number of case reports in which it appears that black cohosh led to severe liver injury. However, it is not clear whether the cause was black cohosh itself or a contaminant present in the product. One highly preliminary study found that black cohosh might reduce the effectiveness of the chemotherapy drug cisplatin. Safety in young children or those with severe liver or kidney disease is not known.

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