Speaking at a science writers' conference sponsored by the American Medical Association, Donald Hensrud, an assistant professor of preventive medicine and nutrition at Mayo, reviewed the results of three studies involving more than 8,000 fen-phen and Redux users published last month in the New England Journal of Medicine (NEJM). Hensrud also reported on the modest success of a new diet drug called sibutramine, which was approved last year by the Food and Drug Administration. Hensrud said that on average sibutramine users lost 15 pounds in six months, when the drug was combined with a program of diet, exercise and behavior modification.

The NEJM studies of fen-phen and Redux found that between 12 and 24 percent of those who took the drugs developed valvular heart disease, a rare and potentially lethal problem that is rarely seen in people under 50. In 1997, when the drugs were withdrawn from the market, the FDA reported that in one study about 30 percent of 290 patients showed signs of heart valve damage.

More than 18 million prescriptions for fen-phen and Redux were written between 1992 and 1997. Phentermine, the second half of the fen-phen combination, remains on the market and is sometimes prescribed as a weight loss remedy for use with Prozac, a practice that is not approved by the FDA and one for which Hensrud says there is no scientific evidence.