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The researchers found that 55.5 percent of women with moderate or severe hot flashes when they began taking hormone therapy experienced them again when they stopped, compared with 21 percent of those on placebo.

For all women in the study, 21 percent had moderate to severe hot flashes after discontinuing, compared with 5 percent of those taking dummy pills.

The journal authors, led by University of Massachusetts Medical School researcher Judith Ockene, said it was unclear how long women experienced renewed symptoms.

Isaac Schiff, head of the American College of Obstetricians and Gynecologists task force on hormone treatment, said the new study quantifies a phenomenon that doctors had long observed.

But Schiff also said he saw nothing in the study to suggest a change in his organization's recommendation that hormone treatment should be available to women with severe menopausal symptoms.

"Some women are going to have to take it for many, many years or else their symptoms will recur," he said.

The Food and Drug Administration now recommends that hormone treatment be used for the shortest time possible, and at the lowest dosage.

Joseph Camardo, a Wyeth senior vice president, said the new study provided no new or su...

Use plummeted after the Women's Health Initiative released its results.

The long-standing belief has been that symptoms subside a few years after women have their last period and that taking hormones might help women avoid symptoms, although strong scientific evidence about the duration has been lacking, Ockene said.

Researchers, she said, "would have assumed that 5 1/2 years, which is the average length in this study, would have been enough time to see them not return." Smith, of Fitchburg, Mass., said she started having menopausal symptoms at age 49, with hot flashes so severe that they steamed up car windows.

They disappeared during the study.

"Within a month they were back again.

Not quite so bad, but I still wake up at night with a good one," Smith, 73, said recently.

The original study involved 16,600 women aged 50 to 79 who were given Smith was among 8,405 WHI participants surveyed by mail eight to 10 months after the study was halted.

Overall, 21 percent of Ockene said those results suggest that many women on fake pills might have gone through natural menopause during the study, while for those on P...