New York: Despite reports of liver damage in some women using black cohosh to ease menopause symptoms, clinical trials testing one major brand of this herb have so far found no evidence that it is to blame, according to a research review.
Extracts of black cohosh, a plant native to North America, are marketed as a "natural" form of hormone replacement therapy (HRT) and are most commonly used to treat hot flashes and other symptoms of menopause.
Studies so far have come to conflicting conclusions about whether black cohosh works.
There have also been concerns raised about its safety. Reports of liver inflammation and liver failure in a small number of black cohosh users prompted some countries, like Australia and the UK, to require warning labels on the products.
But it has never been clear that black cohosh was to blame for those cases of liver damage. In most cases, doctors were unable to account for the patients' drinking habits or use of medications that can harm the liver.
And many postmenopausal women who are plagued by hot flashes and night sweats prefer to try black cohosh instead of taking hormones. Hormone replacement therapy, or HRT, has been controversial since 2002, when the Women's Health Initiative, a massive government-sponsored clinical trial, found that women on HRT had higher rates of heart attack, stroke, breast cancer and blood clots than placebo users.
Experts now advise that while HRT is effective for menopausal symptoms, women should take the lowest possible dose for the shortest time possible.
For the new study, reported in the journal Menopause, researchers combined the results of five previously published clinical trials of the black cohosh product Remifemin. Together, the studies involved more than 1,100 women who used either this black cohosh product or a comparison substance -- either an inactive placebo or a hormonal medication called tibolone -- for three to six months.
Overall, the researchers found, 88 women dropped out of the studies, but none did so because of abnormal liver enzymes, a potential sign of liver damage.
And there was no evidence that black cohosh triggered harmful changes in liver enzymes. In both the black cohosh and comparison groups, about 5 percent of women developed abnormally high levels of a liver enzyme known as AST.
On the other hand, of 37 black cohosh users who had abnormally high AST levels before treatment, 62 percent saw those levels drop back into the normal range during therapy.
The study was led by Dr. Belal Naser of Salzgitter, Germany-based Schaper & Brummer GmbH & Co., which manufactures Remifemin.
But an expert not involved in the study said the findings are consistent with other evidence that black cohosh is safe for the liver.
Dr. Richard B. van Breemen, a professor at the University of Illinois College of Pharmacy in Chicago, was part of a 2009 clinical trial that tested black cohosh against a placebo, standard hormone replacement and red clover -- another alternative therapy for menopause symptoms.
They found that over one year, black cohosh was no better than the placebo for easing hot flashes and night sweats.
But there was also no evidence that the herb harmed women's liver function.
"Although black cohosh did not prevent hot flashes in menopausal women in our study, we found that black cohosh was safe," van Breemen told Reuters Health in an email. "In particular, we tested for liver damage in our study and found that black cohosh was not hepatotoxic (toxic to the liver)."
That trial, which was funded by the U.S. National Institutes of Health, was not included in the current analysis -- which focused only on trials of Remifemin.
That narrow focus, van Breemen noted, is a weakness of the study.
Still, he said, "the conclusion...that black cohosh does not cause liver damage is consistent with the results of our investigation and many other clinical trials."
In general, experts do advise that women stop using black cohosh and tell their doctor if they develop any potential signs of liver toxicity, including abdominal pain, dark urine or jaundice (yellowing of the skin and whites of the eyes).
Three months worth of Remifemin tablets costs about $30 in the U.S. -- roughly the same as Premarin, a widely used hormone replacement drug.
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