Hot flashes—sudden, uncomfortable momentary sensations of heat that may be accompanied by a red, flushed face and sweating—are the number one reason women seek medical attention for menopausal symptoms . In the past, women have turned to hormone replacement therapy (HRT) to control their hot flashes. But recent studies showing an increased risk of cardiovascular disease and breast cancer associated with such treatment have left women looking for alternatives.

Dietary supplements made from red clover are marketed as an alternative treatment for menopausal symptoms. Red clover contains isoflavones , a group of naturally occurring substances (also plentiful in soy products) with properties similar to estrogen. Yet, while natural remedies for hot flashes are commonly used and readily available, little is known about the safety or efficacy of red clover.

Researchers set out to investigate whether Promensil and Rimostil, two dietary supplements derived from red clover, are safe and more effective than placebo for reducing hot flashes and improving quality of life in symptomatic postmenopausal women. The results, which are published in the July 9, 2003 issue of the Journal of the American Medical Association (JAMA), indicate that supplements containing red clover have only a modest effect on hot flashes.

About the Study

The researchers randomized 252 postmenopausal women ages 45 to 60 years old, who were experiencing at least 35 hot flashes per week into one of three groups: Promensil (82 milligrams (mg) of total isoflavones per day), Rimostil (57 mg of total isoflavones per day), or placebo, and followed for 12 weeks. The study was conducted between November 1999 and March 2001 at three U.S. medical centers.

Women were excluded from the study if they were vegetarian, consumed soy products more than once per week, took medications affecting isoflavone absorption (antibiotics, antacids ) or hormonal preparations during the three months prior to enrollment, or were regular users of dietary supplements containing isoflavones.

Participants were contacted by telephone at weeks one, four, and eight to encourage compliance, assess adverse effects, verify concurrent medications, and obtain follow-up information on hot flashes. Changes in quality of life were assessed using the Greene Climacteric Scale, a tool that gauges the effects of ill health across a number of physical, psychological, and social parameters. At 12 weeks, the participants returned to the clinic sites for a full evaluation.

The Findings

The average number of hot flashes dropped by 41% in the Promensil group, 34% in the Rimostil group, and 36% in the placebo group. The decrease in hot flash frequency was significant for all three groups; however, the reductions in the two treatment groups were not significantly different from placebo group at 12 weeks.

There was some evidence that the benefit of supplements was most pronounced for heavier women (the association was statistically significant with Rimostil, but only suggestive with Promensil). In addition, the reduction in hot flashes was significantly faster for Promensil compared with placebo. There was no statistically significant association of either supplement with adverse events.

Adjustment for differences in study site, season, age at randomization, age at menopause, time since menopause and other potential confounders did not change the results.

An important limitation of this study is that all participants were postmenopausal and highly symptomatic; perimenopausal or less symptomatic women might respond differently to the same treatment.

How Does This Affect You?

This study—the largest randomized clinical trial of red clover extracts in postmenopausal women—suggests that dietary supplements containing red clover have little effect on hot flashes or quality of life, Additional research, however, would be needed to determine why Promensil (but not Rimostil) reduced the frequency of hot flashes more rapidly than placebo and why heavier women appeared to receive more benefit from taking the supplements than thinner women.

Furthermore, because the study lasted only 12 weeks, researchers could not assess long-term risks (such as breast cancer or cardiovascular disease) or benefits (like improvements in quality of life) of red clover. And, although the amount of total isoflavones used in this study was relatively high, it is possible that higher doses are needed to have a clinically important effect.

Estrogen is clearly the most effective known treatment for hot flashes in postmenopausal women, but it is no longer considered perfectly safe. While this study does not seem to support the use of red clover as a substitute, it may be too soon to give up on this treatment. Besides red clover, the herb black cohosh or products containing soy isoflavones may be helpful, but studies to date have been far from conclusive. Women who suffer from hot flashes or other menopausal symptoms should talk to their doctor about their options.