Millions of menopausal women wary of the risks of hormone replacement therapy take botanical supplements instead. But new studies reveal that one such supplement is ineffective and another could be dangerous to certain women.

Women with breast cancer, or who may have undiagnosed breast tumors, should not take the supplement black cohosh for their symptoms, a Duquesne University researcher said yesterday at the American Association for Cancer Research meeting in Washington, D.C.

The lead researcher on the study, Vicki Davis, assistant professor of pharmacology at Duquesne, found that in mice with breast tumors, black cohosh increased the risk that the cancer would spread to the lungs. The tumors also appeared to be more aggressive, she said.

The herb doesn't cause breast cancer but increases the chances that breast cancers will spread beyond the breast, which makes them extremely difficult to treat.

Davis used mice that had an activated gene that causes them to spontaneously develop mammary tumors, and fed them black cohosh in amounts comparable to those normally taken by women.

"The mouse model I used is one that is very similar to human breast cancer," Davis said. "A lot of the mechanisms for metastatic cancer are very similar between the animal and the human."

Davis said they did not yet know how the extract causes more aggressive cancers.

"Black cohosh is a mixture of compounds," she said. "We don't know if the ones that are helping the symptoms are different from the ones that are affecting the cancer."

Another widely used botanical supplement, red clover, was found ineffective in a study published Wednesday in the Journal of the American Medical Association. Dr. Jeffrey Tice of the University of California, San Francisco, found that red clover supplements were no more effective at treating hot flashes and other menopausal symptoms than a placebo.

Davis warned against the widespread misconception that such compounds as black cohosh and red clover are safer than synthetic drugs because they are "natural."

"We shouldn't assume all natural products are safe," she said.

With therapies being discredited, women are left with few options for treating menopausal symptoms and new ones must be developed, Davis said. "Hot flashes and menopausal symptoms are not minor problems."