Harvard Women's Health Watch

In Brief: Hot flash herb no better than placebo in large trial

In Brief

Hot flash herb no better than placebo in large trial

Black cohosh is the most popular herbal supplement used by perimenopausal and menopausal women, but its effectiveness against hot flashes and night sweats remains unproven. The herb, extracted from the roots and underground stems (rhizomes) of a perennial plant native to North America, is available over the counter in tablet, liquid, or capsule form. While there's no dearth of black cohosh studies, their inconsistency in design and results have made it difficult to evaluate the herb's effectiveness and safety, especially beyond three months.

In the longest and largest placebo-controlled trial to date, researchers have found that black cohosh — used alone or with other botanical supplements — is no better than placebo in relieving hot flashes and night sweats. The yearlong investigation, called the Herbal Alternatives (HALT) for Menopause Study, was funded by the National Institutes of Health. Results were published in the Dec. 19, 2006, Annals of Internal Medicine.

The HALT researchers randomly assigned 351 women, ages 45–55 and with an average of six hot flashes per day, to receive one of five therapies: black cohosh alone; a multi-botanical supplement containing black cohosh; the black cohosh–containing multibotanical plus advice to increase soy intake; hormone therapy (estrogen with or without a progestin); or a placebo. After one year, there was no significant difference in hot flash frequency (or intensity) between any of the three black cohosh groups and the placebo group. On the other hand, women taking hormone therapy had, on average, four fewer hot flashes per day than women receiving the placebo. There were no significant differences in reported side effects, except the hormone therapy group noted more breast pain and menstrual difficulties.

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