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There is little evidence to show herbal remedies purported to relieve symptoms of menopause actually work, according to a new study.

A growing number of women have turned to black cohosh, evening primrose oil and other natural remedies in recent years to treat hot flashes, irritability and other related problems. Evidence that hormone replacement therapy is associated with a risk of heart disease, stroke and other cardio-vascular problems also may have increased the number of women looking for alternatives to prescription treatments for menopausal symptoms.

But evidence demonstrating the effectiveness of these remedies is often under-researched, weak or even "non-existent," according to a new report.

The report appears in this month's edition Drug and Therapeutics Bulletin, published by the British Medical Journal.

"A lot of treatments have become established with time in terms of people trying them out. But if you were looking for cast-iron evidence for lots of treatments you wouldn't be able to find it," said Ike Iheanacho, editor of the bulletin.

The report evaluates studies that have been conducted on the effectiveness of black cohosh, red clover and other non-prescription treatments for symptoms of menopause. Some herbs, such as ginseng, are used to help a variety of conditions, and also touted by health-care groups and some manufacturers as ways to ease symptoms associated with menopause as well as premenstrual syndrome.

But much of the supporting evidence is contradictory or weak, according to the bulletin.

Black cohosh: The report revealed contradictory evidence. Several studies found that women who took black cohosh over a period of time reported no major difference in hot flashes or other menopausal symptoms compared with women given placebo. Other studies found the herbal remedy did provide some relief to some women. The product has also been associated with increased risk of liver toxicity and was subject to a Health Canada warning in 2006 as a result.

Red clover: A review of 30 trials found no major difference in menopausal symptoms among women who took red clover extracts compared with placebo. Red clover contains phytoestrogens, which are believed to deliver estrogen-like effects, but it's not clear how this occurs or what the benefits are, the report said.

Dong quai: It's a plant popular in traditional Chinese medicine that has been used to help women in a variety of ways, including recovery from childbirth and relief of menopausal symptoms. One study found no difference between dong quai and placebo in reducing hot flashes. Another found dong quai combined with chamomile resulted in a decrease of hot flashes compared with placebo.

Evening primrose oil: A review of one study found no difference in menopausal symptoms in women who took the herbal remedy compared with women who took placebo.

Ginseng: A review of two studies found women who took it for menopausal symptoms experienced no significant benefit compared with those who took placebo.

That's not to say herbal remedies have no benefit, Dr. Iheanacho said. But as more consumers turn to natural remedies, it's important to provide better, more credible evidence on how well these therapies work, what the potential risks are and who they are best suited for, he said.

In many countries, including Canada, natural health products can be approved for sale as long as the manufacturer can show they have been used as a herbal remedy for decades.

As a result, some companies may be reluctant to invest the kind of cash necessary to finance more extensive and potentially conclusive studies, especially if it won't affect their ability to market their product, he said.

Health Canada created a bureau several years ago to license natural health products and regulate their sale. But it's been overwhelmed with applications, meaning there are still many unlicensed natural health products on the market.

Some health experts have criticized Health Canada for not requiring more conclusive trials, such as those conducted by drug companies, to provide better proof of a natural product's safety and effectiveness.

However, one naturopathic doctor said herbs are much different than drugs and shouldn't necessarily be subject to the same type of standards. It may be better to track their use and any reported side effects, in addition to doing research, to get a better sense of their effectiveness, said Kieran Cooley, assistant professor at the Canadian College of Naturopathic Medicine in Toronto.

He said that type of initiative will require improved government funding, particularly considering how many Canadians are now using natural therapies. "As we start collecting better data, we get a better understanding."