The herb black cohosh, or Actaea racemosa (formerly named Cimicifuga racemosa), is native to North America. The roots and rhizomes are widely used in the treatment of menopausal symptoms and menstrual dysfunction. Black cohosh was originally used by Native American peoples in the treatment of many conditions, especially gynecologic disorders.¹ The most widely used and best studied commercial formulation available in the United States is Remifemin, an extract of the rhizome that is produced by a German company. Numerous other brands of black cohosh are available, but not all are standardized extracts. Black cohosh should not be confused with the blue cohosh herb (also known as Caulophyllum thalictroides), which is used for different indications and has a greater potential for toxicity.

Pharmacology

The primary active constituent of the black cohosh root is believed to be the terpene glycoside fraction, including actein and cimifugoside. The rhizome also contains other potentially biologically active substances, including alkaloids, flavonoids, and tannins. The therapeutic activity of black cohosh was originally believed to derive from an activation of estrogen receptors; however, more recent studies^2,3 show that although some constituents of the extract bind to at least one subtype of estrogen receptors, this binding produces very little, if any, estrogenic effect, and may selectively block some of these effects.

One early study⁴ reported that treatment with black cohosh produced a decrease in luteinizing hormone (LH) levels consistent with an estrogenic effect; however, more recent studies^5,6 have shown no effect on levels of LH, follicle-stimulating hormone (FSH), or prolactin. It remains unclear whether black cohosh exerts its effect via estrogen receptors or through another mechanism.

Uses and Efficacy

Currently, the primary use of black cohosh extract is for alleviation of menopausal symptoms. The American College of Obstetrics and Gynecology guidelines on the use of botanicals for the management of menopausal symptoms support this use for up to six months, especially in treating the symptoms of sleep and mood disturbance, and hot flushes.⁷ [Evidence level C, consensus/expert guidelines] At least eight studies of black cohosh therapy for menopausal symptoms, involving approximately 2,000 women, have been published, most of them in German.³ Many of these studies used an estrogen product in the control group, and most of the trials used standardized outcome measures such as the Kupperman Menopause Index and the Hamilton Anxiety Scale. Almost all of these studies demonstrate efficacy in patients taking black cohosh extract similar to that of estrogen in the treatment of neurovegetative menopausal symptoms. Unfortunately, most of these studies are open trials and lack blinding and long-term follow-up, making it difficult to draw definitive conclusions from their results.

As with other herbal medicines believed to have potential estrogenic effects, there has been a concern about the safety of black cohosh in women with a personal history or strong family history of breast cancer. Although further research is needed, at least one tissue-culture study² showed no stimulation of estrogen receptor–positive breast cancer cell lines by black cohosh extract. This study² found that black cohosh extract increased the inhibitory effect of tamoxifen (Nolvadex) on the breast cancer cell lines. Because this question has not yet been resolved, physicians should discuss the issue with their patients who are at risk for breast cancer and are considering taking black cohosh. In a study that included 69 patients and examined black cohosh as a treatment for hot flushes in women with breast cancer, it was found to be no more effective than placebo, regardless of whether the hot flushes were induced by tamoxifen or by natural menopause.⁶ [Evidence level A, randomized controlled trial]

Black cohosh also has been used to treat dysmenorrhea and is recommended for this indication by the German Commission E,⁸ which establishes guidelines for the proper use of herbs in Germany. However, this recommendation is based on case reports, and there are no randomized clinical trials supporting the use of black cohosh for this indication.

Interactions, Adverse Effects, and Contraindications

With the exception of a possible interaction with tamoxifen, there are no known interactions between black cohosh extract and any medications.⁸ In clinical studies,⁸ the only adverse effect reported with any significant frequency was gastrointestinal discomfort. In larger doses, black cohosh can cause dizziness, headaches, giddiness, nausea, and vomiting.⁹ One case report¹⁰ centers on a woman who developed a seizure after taking a combination of black cohosh, chasteberry, and evening primrose oil, but no clear cause-and-effect relationship was documented. No other reports of seizure in association with black cohosh have been published.

Black cohosh is contraindicated during pregnancy because of its potential ability to stimulate uterine contraction.¹¹ The safety of black cohosh in breastfeeding mothers and the degree of transmission of black cohosh in breast milk are unknown. Controversy remains regarding the safety of black cohosh in women with a personal history or strong family history of breast cancer.

Dosage

Most studies of black cohosh have used the extract known as Remifemin, which is standardized to contain 1 mg of terpene glycosides per 20-mg tablet. The most commonly used dosage of Remifemin is two 20-mg tablets twice daily. Maximum effect usually occurs in four to eight weeks.

Recent information from the manufacturer suggests that a dosage of 20 mg twice daily may be as effective in the treatment of menopausal symptoms as 40 mg twice daily.⁵ Black cohosh extract also is available in tincture form; the proper dosage of the tincture is 2 mL twice daily of a 1:1 tincture in 90 percent alcohol.⁸

Final Comment

Although the clinical trials on black cohosh are of insufficient quality to support definitive statements, this herbal medicine does appear to be effective in the short-term treatment of menopausal symptoms. The mechanism of action is unclear, and early reports of an estrogenic effect have not been proved in recent studies. Some patients will assume that, because black cohosh provides some of the same benefits as hormone therapy in terms of symptom control, the additional salutary effects of hormone therapy can be achieved with the use of black cohosh. Physicians should be quite clear in explaining to their patients that although black cohosh may be useful in treating some menopausal symptoms, there is currently no evidence regarding any protective effect of black cohosh against the development of osteoporosis.

An additional concern exists about the safety of this herb in long-term use, particularly the possibility that it can cause long-term unopposed estrogenic stimulation of the endometrium, thus raising the risk of development of endometrial cancer. Although studies have not shown any effect on vaginal cytology, the effect of black cohosh extract on the endometrium has not been adequately studied. Some physicians recommend that women using black cohosh on a long-term basis be given a progesterone as well. Table 1 discusses the efficacy, safety, tolerability, and cost of black cohosh.