There is little scientific evidence that herbal remedies commonly used to treat menopausal symptoms work, and some may be dangerous if taken along with other treatments, according to a review published on Wednesday.

Black cohosh, red clover, Dong quai, evening primrose oil and ginseng are taken to ease hot flashes, sleeplessness and diminished sex drive in the belief that they are natural products without risk, said Ike Iheanacho, editor of the journal Drug and Therapeutics Bulletin, who wrote the review.

"In reality, however, herbal medicines have pharmacological actions, and so can cause unwanted side effects and have potentially dangerous interactions with other medicines, both herbal and conventional," he wrote.

An estimated 30 to 70 percent of women in industrialized countries experience menopause-related symptoms caused by a sharp fall in estrogen levels. On average they last for around four years but for some women they persist much longer, Iheanacho said.

Hormone replacement therapy was a popular treatment until 2002, when a major study suggested it might increase the risk not only of breast and ovarian cancer, but also of strokes and other serious conditions.

Iheanacho's review of previously published studies, scientific commentary and other sources found mixed evidence on whether black cohosh relieved menopausal symptoms effectively and no strong data showing red clover extract works.

There was also no evidence that Dong quai, evening primrose oil, wild yam, chaste tree, hops or sage make much difference,

he added in the review that included 26 published studies.

"There is little evidence either way on whether they work," Iheanacho said in a telephone interview.

The findings also underscore the fact there is little good quality evidence on the effectiveness of herbal medicines or how they may react with prescription medicines, Iheanacho wrote.

Published studies are often poorly designed, include too few participants or do not last long enough to be of real value for the products, which are often unlicensed, he added.

"There are a fair number of studies but when you drill it down to the ones that can give you useful information, those are in the minority," Iheanacho said.