What Is Black Cohosh?

Medically Reviewed

What it is: Cimicifuga racemosa, often called black cohosh, black snake root, or rattleweed, is a native American plant long used to treat “female complaints.” Found today in various products (such as Remifemin and Black Cohosh Power), it is one of the best­selling herbs for symptoms of menopause, especially in Europe.

Claims, purported benefits: Relieves menopausal symptoms such as hot flashes, headaches, and insomnia; effective against menstrual cramps. Safer than hormone therapy.

What the science says: Some studies have found that it relieves hot flashes, sweating, headaches, and other menopausal symptoms, but few were well designed, and on the whole the results have been inconsistent. Complicating matters is the fact that different species, preparations, and doses of Cimicifuga have been used in studies and are found in products on the market.

It’s unclear what effects black cohosh has in the body since it contains at least 50 compounds with proposed biological effects, including some with estrogenic activity (though some analyses have found no estrogenic or other hormonal effects). Other substances in black cohosh may bind to opioid receptors (and thus have analgesic properties) or affect serotonin levels in the brain. It’s unknown whether black cohosh has an effect on breast cancer risk. It is also not clear whether women taking birth control pills or hormone replacement therapy can safely take black cohosh.

In 2006, in the Archives of Internal Medicine, a systematic review of studies cited some evidence that the herb can be helpful against hot flashes. However, results from a well­designed, federally funded, one­year trial, published in the Annals of Internal Medicine also in 2006, found that black cohosh was no better than a placebo (and less effective than hormone therapy) for hot flashes and sweating.

In 2009, a study in Menopause found that black cohosh (as well as red clover) works no better than a placebo for hot flashes and other menopausal symptoms. In fact, the placebo worked better. Only hormone therapy was found to be effective. A 2012 review by the Cochrane Collaboration of 16 studies concluded that there is no evidence that black cohosh is more effective than a placebo in relieving hot flashes.

Special precautions: It may be a mild sedative, so avoid taking it if you are taking tranquilizers. And it may interact with certain hypertension or cholesterol medications.

Common side effects: A few years ago, British authorities warned that black cohosh could cause liver damage and ruled that all such products must carry a warning. Since then, some researchers have questioned this potential risk, noting that other herbs and factors (such as impurities and adulterants in collecting or processing the herb) may have been to blame in the reported cases. As stated in an editorial in the journal Menopause in 2011, “there is no way to know with any certainty at this time” whether black cohosh can cause liver toxicity. The herb is listed as a cause of acute liver damage in a new database from the National Institutes of Health, which notes that this may be “an idiosyncratic reaction.”

Less serious side effects include stomach upset, headache, dizziness, and weight gain. Women who are pregnant or breastfeeding should steer clear of it. Even its advocates say that women who try it for menopausal symptoms should not take it for more than six months, though others say three months.

A note about quality control: A chemical analysis of eleven commonly available black cohosh products, published in the Journal of Agricultural and Food Chemistry, found that three did not even contain black cohosh, but a cheaper herb; products that did contain the right herb had widely varying amounts.

Our advice: Research results have been mixed, at best, and it’s impossible to recommend any particular black cohosh products. If you try black cohosh, be sure your doctor knows so he/she can monitor your liver function, just to be on the safe side.