The bad news about hormone therapy just keeps getting worse. New findings from the largest study of hormone replacement therapy indicate that older women taking a combination of estrogen plus progesterone have twice the risk of developing Alzheimer's disease and other dementias as do women taking a sugar pill, or placebo. None of the 4,532 women over 65 in the Women's Health Initiative Memory Study (WHIMS) had dementia prior to the trial. Half took Wyeth's drug Prempro and half the placebo. At the trial's end four years later, 61 had developed dementia--40 on HRT and 21 taking the placebo. "We see a clear and significant risk of dementia for women taking the combination hormone therapy," says Sally Shumaker, professor at Wake Forest University School of Medicine and a lead WHIMS researcher.

Older observational studies had raised hopes that hormones might actually slow development of Alzheimer's, which afflicts 10 percent of people over 65 and 50 percent of those 85 years or older. According to Shumaker, there's been an upsurge in the number of older postmenopausal women who have turned to hormone replacement therapy to prevent memory loss and mental decline. But when WHIMS researchers looked only at the women in the high-risk group (who had suffered a stroke or had low cognitive test scores), combination HRT "did not slow the dementia, as many had hoped," says Shumaker. "It accelerated it. Clearly, there is no reason for older women to take combination HRT."

Researchers emphasize that the risk of dementia for any one woman taking HRT is small. And Wyeth, the maker of Prempro, notes that the study applies only to older women. Most HRT users are newly menopausal and taking the drugs to relieve symptoms such as hot flashes. WHIMS researchers will follow the participants to see if their risk of dementia declines after they stop using HRT.