Black cohosh (Cimicifuga racemosa) is a perennial herb that has been widely used for relief of hot flashes due to menopause, menstrual cramps, and premenstrual syndrome (PMS). Whether or not the herb really works to quell hot flashes remains a scientifically unsettled issue, although many women and some doctors are convinced it does. The question of its safety for women who have had breast cancer (or those like yourself with a family history of breast cancer) has been at issue until recently.
Fredi Kronenberg, PhD, director of the Rosenthal Center for Complementary and Alternative Medicine at Columbia University in New York City, has recently concluded laboratory research on the estrogenic effects of black cohosh on breast cancer cells. Her research has shown that the herb contains no formononetin, an estrogenic isoflavone, as had been previously reported. She also found that black cohosh has no estrogenic effect on breast cancer cells in a test tube. This doesn't mean that black cohosh is completely safe for women who take it, but Dr. Kronenberg tells me that "it's as close as we can get to that conclusion right now." With these findings, I think you can assume that taking black cohosh will not increase your risk of breast cancer.
Your doctor's concern that by using black cohosh for relief of hot flashes you will, in effect, be taking estrogen without the benefit of progestin (synthetic progesterone) is, I think, unfounded. It stems from the fact that when only estrogen is replaced, this hormone can overstimulate the uterine lining, leading in some cases to endometrial cancer. Of course, this isn't a problem among women who have had hysterectomies. For women with a uterus who decide to take hormone replacement therapy after menopause, progestin is prescribed to counteract the effects of estrogen on that organ. However, studies are increasingly finding no estrogenic effect for black cohosh, and a recent double-blind study found the herb had no estrogen-like effects on the uterus or vagina.
Overall, the jury is still out on whether black cohosh reliably relieves menopausal symptoms - and if so, how - as well as whether it may pose any long-term dangers. As far as side effects go, the herb may occasionally cause mild digestive distress. Studies in rats have not found any significant toxic effects at 90 times the therapeutic dosage over a six-month period, but studies have not looked at long-term effects in other animals or humans.
Even if black cohosh relieves your hot flashes, there's no good evidence to show it protects against the postmenopausal bone thinning that leads to osteoporosis as hormone replacement therapy does. So, all postmenopausal women should be getting 1,000 to 1,200 mg of calcium daily from food, supplements, or both as well as doing regular weight-bearing activity (such as walking) plus exercises that improve strength, balance, and flexibility.
Andrew Weil, M.D.