The Food and Drug Administration (FDA) should warn women that preliminary research suggests that the herbal supplement black cohosh may increase the risks of breast cancer metastasis and liver failure, according to the Center for Science in the Public Interest (CSPI). CSPI also called on the National Institutes of Health, which is studying the effectiveness of black cohosh in relieving hot flashes and other symptoms of menopause, to advise study subjects of the possible risks and to be on alert for any adverse effects. Drug and supplement makers are increasingly marketing black cohosh to menopausal women in the wake of the safety concerns raised over hormone replacement therapy.

In mice given black cohosh, breast cancer was more likely to spread to the lungs, according to a new study that CSPI forwarded to the FDA. And at least three cases in the medical literature have linked liver toxicity in women to herbal remedies containing black cohosh. Two of the women required liver transplants to survive. Although labels for many commercial preparations of black cohosh warn that pregnant or nursing mothers should not take it, no labels warn about risk of cancer or liver problems.

“Women, particularly women who have had breast cancer, should think twice before taking black cohosh,” said CSPI senior nutritionist David Schardt.

In a letter to FDA Commissioner Mark McClellan, CSPI said that the FDA should also notify physicians about the potential risks of black cohosh, and urge them to submit any data on liver toxicity or cancer metastasis from patients taking black cohosh.

“Women taking black cohosh should be monitored for evidence of liver problems,” said Stanley M. Cohen, M.D., of Rush Medical Center in Chicago. “If physicians look for this, we’ll be seeing more cases.” Cohen reported a case of hepatitis in a patient who took black cohosh for three weeks.

Concerns over hormone replacement therapy were renewed last week when a second government-sponsored study was halted for safety reasons. According to CSPI, supplement manufacturers may again be eager to exploit those concerns and aggressively market black cohosh as a substitute.