Black cohosh, a medicinal herb increasingly used by women as an alternative to estrogen replacement therapy, may reduce hot flashes by targeting serotonin receptors — some of the same receptors used by the brain to help regulate body temperature — according to a team of researchers from the University of Illinois at Chicago. The finding, the first to demonstrate a possible mechanism of action for the herb other than estrogen, increases the likelihood that the herb is safe to use, they say.
The study was described today during a press briefing on hormone replacement therapy at the 226th national meeting of the American Chemical Society. The study also will appear in the Sept. 10 issue of the Society's Journal of Agricultural and Food Chemistry.
Until now, many scientists thought that black cohosh worked by targeting receptors for estrogen, the same hormone used in commercial hormone replacement medicine that has recently been associated with adverse side effects, including breast cancer and stroke.
"This study shows that black cohosh does not appear to be estrogenic whatsoever and, as a result, is less likely to pose some of the dangers associated with traditional estrogen replacement therapy," says study leader Judy L. Bolton, Ph.D., a professor at the university's College of Pharmacy.
"We now have new clues to how it might work in the body."
Although preliminary evidence of the herb's efficacy in relieving hot flashes, night sweats and other symptoms of menopause is encouraging, further studies are still needed before it can be recommended, Bolton says. Long-term safety data on black cohosh is also needed, she adds.
To determine whether black cohosh is estrogenic, the researchers used a group of rats whose ovaries had been removed. The rats were divided into different groups and each group was fed a different concentration of cohosh extract daily for two weeks. Extracts of the herb, either alone or in combination with synthetic estrogen, did not produce any changes in uterine weight or vaginal cell differentiation in the animals. This indicates that the herb has no estrogenic effects, the researchers say.
In accompanying lab studies, the researchers also demonstrated that the black cohosh extract is capable of binding to human serotonin receptors, including those that help regulate body temperature. Previous studies have shown that these receptors may play a role in regulating hot flashes. Antidepressant medications, which some people believe may help reduce hot flashes, also bind to the same receptors. The current study may help provide an explanation for this effect, Bolton says.
Researchers still do not know the specific chemical or chemicals in black cohosh that target the serotonin receptors. Nor do they know if the herb may target hot flashes via additional mechanisms. Further studies are underway to find answers to these questions, they say.
A Phase II clinical trial involving women with a high frequency of hot flashes is now underway at the university to determine whether black cohosh actually reduces the frequency and intensity of hot flashes and other menopausal symptoms. The women will either receive black cohosh, red clover, a placebo or estrogen replacement during the one-year trial, which is one of the largest and longest of its kind, according to Bolton. The trial is funded by the National Institutes of Health. Black cohosh is indigenous to North America and is used by many women to treat menopausal problems. Native Americans originally used it to treat a variety of ailments, including gynecological disorders and even depression. Interest in the herb has soared following the recent findings of the Women's Health Initiative study, which showed that the health risks of estrogen replacement therapy, including breast cancer and stroke, might outweigh its benefits for some women.