Researchers have stopped a large trial of women taking estrogen replacement therapy because the estrogen wasn't improving their health and may have slightly increased their risk of stroke. Halted in February 2004, the trial involved almost 11,000 women who were taking Premarin, an estrogen-only medication made from the urine of pregnant mares. After 7 years of follow-up, researchers from the National Institutes of Health concluded that the drug had no effect on the risk of heart disease and decreased the risk of hip fracture. However, the drug seemed to slightly increase the risk of stroke.

This is the second large trial studying hormone replacement therapy (HRT) that researchers have stopped early; both were part of the Women's Health Initiative. In a trial stopped in 2002, women were taking estrogen plus progestin. That trial ended early because researchers linked the medication to an increased risk of heart attack, stroke, and some forms of cancer.

Researchers had hoped that taking estrogen alone would benefit women during and after menopause, but their findings don't support that theory. For more information, visit the "News/Events" section on the Web site of the National Heart, Lung, and Blood Institute at http://www.nhlbi.nih.gov.