The study is a validation of something cancer specialists stumbled upon several years ago that is now becoming known by the general medical community, says Dr. Vered Stearns, an assistant professor of oncology at the Johns Hopkins School of Medicine and lead author of the report in the June 4 issue of the Journal of the American Medical Association.

The antidepressant is not quite as effective as hormone replacement therapy (HRT) for hot flashes, which can reduce their frequency by up to 90 percent. But HRT has fallen sharply out of favor because a large-scale study shows it increases the risk of heart attack, stroke, breast cancer and dementia.

About 75 percent of women go through hot flashes during menopause, sometimes two or three times a day, sometimes for as long as five years.

The newly reported study used paroxetine, a member of the family of antidepressants called selective serotonin reuptake inhibitors (SSRIs), and was financed by GlaxoSmithKline, which markets it as Paxil.

But other SSRIs, antidepressants in other chemical families, and at least one drug unrelated to depression treatment have been shown to have similar effects on hot flashes.

For example, physicians at the University of Michigan reported earlier this year results similar to those in the new report using not only Paxil but several other SSRIs. Stearns was at the University of Michigan when the Paxil study began.

And doctors at the University of Rochester in New York had such good results with gabapentin, an anticonvulsant marketed as Neurontin, in reducing hot flashes that the university has obtained a patent for that specific use.

Much of the work on antidepressants and hot flashes has been done by cancer specialists, who discovered their effect in treating breast cancer patients. These women cannot be given hormone therapy for medical reasons.

No one really knows why these drugs are effective against hot flashes, says Dr. Thomas Guttuso Jr., a senior instructor in neurology at the University of Rochester who led the gabapentin effort.

"Not a lot is known about what causes hot flashes," Guttuso says. "Most likely gabapentin has some effect on the hypothalamus," the brain center that controls hot flashes.

The Johns Hopkins study enlisted 165 women who were having daily hot flashes. About a third took 25 milligrams a day of a slow-release form of Paxil, a third took 12.5 milligrams a day of the drug, and a third took a placebo.

After six weeks, the number of daily hot flashes was reduced from 7.1 to 3.8 for those taking the 12.5-milligram dose and from 6.4 to 3.2 for those taking the 25-milligram dose. There was a much smaller drop, from 6.6 to 4.8, in the placebo group.

What makes this study significant, Stearns says, is the participating women were not cancer patients. "Most studies have included only breast cancer survivors, because hormone therapy is contraindicated for them," she says. All the women in the study also had not taken any hormone therapy for at least six months.

The study thus shows that antidepressants can be used for all menopausal women having hot flashes, she says. "This is pretty well known in the oncology community, and the news has been spreading to primary-care physicians and gynecologists only in the last year or so," she says.

The effect of antidepressants on hot flashes is clearly different from their effect on depression, she says: "In depression, it takes four to six weeks to see results. In hot flashes you see results in three to four days, and lower doses work as well." But the exact mechanism of action remains unclear.

More information

A comprehensive oversight on hot flashes and other aspects of menopause is available from the National Institutes of Health or the American Academy of Family Physicians.