Black Cohosh

Black cohosh is a shrub-like plant native to the eastern deciduous forests of North America, ranging from southern Ontario to Georgia, north to Wisconsin and west to Arkansas. The dried root and rhizome are used medicinally.¹ When harvested from the wild, the root is black in color. Cohosh, an Algonquin Indian word meaning “rough,” refers to the plants gnarly root structure.²

Native Americans valued the herb and used it for many conditions, ranging from gynecological problems to rattlesnake bites. Some 19th century American physicians used black cohosh for fever, menstrual cramps, arthritis, and insomnia.³

Black cohosh contains several ingredients, including triterpene glycosides (for example, acetin and 27-deoxyactein) and isoflavones (for example, formononetin). Other constituents include aromatic acids, tannins, resins, fatty acids, starches, and sugars. As a woman approaches menopause, the signals between the ovaries and pituitary gland diminish, slowing down estrogen production and increasing luteinizing hormone (LH) secretions. Hot flashes can result from these hormonal changes. Earlier animal studies^{4, 5} and a human clinical trial⁶ suggested that black cohosh had some estrogen activity in the body and also decreased LH secretions. However, more recent animal studies⁷ and a clinical trial⁸ have found no estrogen activity for black cohosh extracts. Further clinical trials are needed to determine whether black cohosh has significant estrogenic actions in the body.

Small German clinical trials support the usefulness of black cohosh for women with hot flashes associated with menopause.^{9, 10} A review of eight clinical trials found black cohosh to be both safe and effective for symptomatic relief of menopausal hot flashes.¹¹ Other symptoms which improved included night sweats, insomnia, nervousness, and irritability. A clinical trial compared the effects of 40 mg versus 130 mg of black cohosh in menopausal women with complaints of hot flashes.¹² While hot flashes were reduced equally at both amounts, there was no evidence of any estrogenic effect in any of the women. Although further trials are needed, this trial suggests that black cohosh is best reserved only for the symptomatic treatment of hot flashes associated with menopause and is not thought to be a substitute for hormone replacement therapy in menopausal and postmenopausal women.

A recent study suggests black cohosh may protect animals from osteoporosis.¹³ Human studies have not confirmed this action.

Black cohosh can be taken in several forms, including crude, dried root or rhizome (300–2,000 mg per day), or as a solid, dry powdered extract (250 mg three times per day). Standardized extracts of the herb are available. The recommended amount is 20–40 mg twice per day.¹⁴ The best researched extract provides 1 mg of deoxyactein per 20 mg of extract. Tinctures can be taken at 2–4 ml three times per day.¹⁵ According to the German Commission E Monographs, black cohosh can be taken for up to six months, and then it should be discontinued.¹⁶

Black cohosh should not be used by pregnant or breast-feeding women.¹⁷ Very large amounts (over several grams daily) of this herb may cause abdominal pain, nausea, headaches, and dizziness.

There is one case report of a woman developing autoimmune hepatitis while using black cohosh.¹⁸ A cause–effect relationship is in doubt, however, because the hepatitis did not resolve after black cohosh was discontinued. A few cases have also been reported in which severe liver failure was attributed to the use of black cohosh.¹⁹ While a cause–effect relationship is difficult to prove, and while such a side effect appears to be rare, people taking black cohosh should be alert to signs of possible liver disease, such as nausea, loss of appetite, fatigue, and tan-colored urine. Black cohosh is not a substitute for hormone replacement therapy during menopause.