IN A DRAMATIC move certain to enflame the long-running debate over hormone-replacement therapy, researchers halted a government-run study of a hormone pill taken by millions of older women. Long-term use of the pill increases the risk of coronary heart disease, invasive breast cancer, strokes and blood clots in the lungs, the researchers said.

The action, which involved Prempro, a popular combined estrogen/progestin pill produced by Wyeth, is likely to change how menopausal women and their doctors approach medical decisions related to aging. The findings come less than two weeks after published research showed that estrogen alone—often sold under Wyeth's brand name Premarin—didn't help protect older women heart patients from further heart disease.

Women have used such drugs for half a century, assured that the medicines provided protection against heart disease and osteoporosis in addition to treating the symptoms of menopause. "I think this is the end of the standard practice of prescribing hormones for long-term disease prevention," says Jennifer Hays, director of the Baylor College of Medicine's center for women's health in Houston, who participated in the study. The study did find that Prempro reduced the incidence of osteoporosis and colorectal cancer, but the dangers were found to outweigh these benefits.