"I couldn't go without it — I have a lot of flashes if I don't take it," says Shirley Waddell, 59, of Jonesville, N.C.

She's talking about the hormone medication she's been taking for the past 20 or so years. The drug, Premarin 625, replaces the estrogen that her body stopped making after she had a partial hysterectomy, which throws a woman, ready or not, right into menopause.

"I just feel better when I take it," she said. About one-fourth of postmenopausal women in the United States are on hormone replacement therapy (HRT). (Postmenopausal is the term doctors use to refer to the entire remainder of a woman's life after she ceases menstruating.) Most women take it for the same reason that Waddell does — to stop the hot flashes that often begin right before menopause and can continue for years afterward. (They take either estrogen or estrogen with a synthetic progesterone called progestin to protect against uterine — or endometrial — cancer.)

Estrogen also helps prevent other symptoms of menopause, such as vaginal dryness. Plus — and this is a big plus for many women — it lowers the risk of developing brittle, easily breakable bones, or osteoporosis. Another reason doctors have encouraged the use of estrogen is to protect women against heart disease, the leading cause of death in postmenopausal women. Early studies suggested that taking estrogen after menopause would decrease the likelihood that a woman will suffer a heart attack.

New Research Reverses Assumptions

But Waddell's experience is one reason doctors are now questioning that claim, and again questioning whether the benefits of estrogen outweigh its risks, particularly the risk of breast cancer. Waddell has heart disease. She had a heart attack in 1991, and in 1998 she underwent a procedure to open up a clogged artery that was restricting blood flow to her heart. Over the past three years she participated in a large study examining the long-held belief that taking estrogen reduces heart disease.

In the study, researchers gave women who already had heart disease either estrogen or inactive "placebo" pills. They didn't tell the women which medication they were on. At the beginning and end of the study, they took angiograms, a type of X-ray picture, of the women's arteries.

The angiograms revealed that estrogen failed to improve the atherosclerosis, or plaque buildup in the arteries that blocks the flow of blood and is a major cause of heart attack and stroke, reported David M. Herrington, M.D., and colleagues in the August 24, 2000, New England Journal of Medicine.