Last Updated: 2011-01-28 17:35:11 -0400 (Reuters Health)
By Amy Norton
NEW YORK (Reuters Health) - 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.
For the new study, reported online January 11th in 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 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.
And there was no evidence that black cohosh triggered harmful changes in liver enzymes. In both the black cohosh and comparison groups, about 5% of women developed abnormally high levels of aspartate aminotransferase. On the other hand, of 37 black cohosh users who had abnormally high AST levels before treatment, 62% 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 it 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," Dr. 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, Dr. 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."
Three months worth of Remifemin tablets costs about $30 in the U.S. -- roughly the same as Premarin, a widely used hormone replacement drug.
SOURCE: http://bit.ly/gANnQZ
Menopause 2011.
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