The prescription diet pill Meridia (sibutramine), when combined with behavior therapy, helped hundreds of very obese teens lose an average of 14 pounds over a year, while those who received a placebo gained four pounds, according to researchers.

The report in the July 18 Annals of Internal Medicine of the multi-center trial involving kids aged 12 to 16 -- and the attendant publicity -- seems likely to cause some ripples at the U.S. Food and Drug Administration, which currently does not approve use of Meridia in adolescents under 16.

One of the concerns that has been expressed about the new diet drug Acomplia (rimonabant), which currently is awaiting FDA action, is that it may wind up being taken by thousands of obese teens even though it would not initially be approved for that group.

"This is the first large multicenter trial of sibutramine for obese adolescents," said study leader Dr. Robert I. Berkowitz, chief of Child and Adolescent Psychiatry at The Children's Hospital of Philadelphia. "In fact, there have been few trials evaluating any obesity drugs in adolescents."

Berkowitz said that in addition to reductions in body mass index and weight, Meridia helped lower triglycerides and increase HDL (good) cholesterol in the treated teens. He said the only significant side effect was tachycardia, or rapid heart beat.

The study enrolled 498 severely obese adolescents at 33 outpatient clinics throughout the United States from 2000 to 2002. The patients were randomized into two double-blinded groups, one receiving Meridia and one receiving a placebo, while both groups received behavior therapy.

Each treatment center had its own behavior therapy program, with flexible modification approaches that included self-monitoring of eating habits and physical activity, stress management, stimulus control, problem solving and social support. Counselors encouraged patients to increase their physical activity and reduce their sedentary behaviors, and provided nutritional counseling.

At the end of the study, the 281 adolescents in the treatment group lost an average of 14 pounds, while the 79 patients in the control group gained an average of four pounds. Body mass index (BMI) decreased by 9.4 percent in the treatment group compared to 1.2 percent in the control group.

Patients in both groups gained height and matured sexually at the same rate.

"At the end of a year of treatment, one-third of the adolescents who received medication were no longer severely overweight, and one out of six who were treated dropped below the standard definition of being overweight," said Berkowitz.

"Although much research remains to be done, our findings are encouraging for clinicians, and may offer treatment options for obese adolescents for whom behavioral therapies alone are not successful," he added.