What is Black Cohosh?

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. 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 as well as other symptoms of menopause.

In the past, black cohosh was believed to be a phytoestrogen, a plant-based substance that has actions similar to estrogen. However, as we describe below, growing evidence indicates that black cohosh does not have general estrogen-like actions. Rather, it may act like estrogen only in certain places: the brain (reducing hot flashes), bone (potentially fighting osteoporosis), and vagina (reducing vaginal dryness).

Black cohosh has also been tried for reducing hot flashes in women who have undergone surgery for breast cancer, but it does not appear to be...

Safety Issues

Black cohosh seldom produces any side effects other than occasional mild gastrointestinal distress. One rigorous study looked for possible deleterious effects on cholesterol levels, blood sugar, and blood coagulability, and did not find any.

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. 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. However, black cohosh has not yet been subjected to large-scale studies similar to those conducted for estrogen. For this reason, safety for...