"We know that being overweight has many adverse consequences, including an increase in the risk of heart disease and type 2 diabetes," noted Dr. Douglas Throckmorton, deputy director for FDA's Center for Drug Evaluation and Research. "OTC orlistat, along with diet and exercise, may aid overweight adults who seek to lose excess weight to improve their health."

The nonprescription pill, to be sold as "alli" by GlaxoSmithKline, blocks the absorption of about 25 percent of fat consumed. It is a reduced-strength version of Roche's popular prescription weight-loss drug Xenical.

Using alli in the absence of a diet and exercise program would be unlikely to provide any benefit, according to Dr. Charles Ganley, FDA's director of nonprescription products. Used in conjunction with diet and exercise, it can boost weight loss by 2-3 additional lbs. for every 5 lbs. lost, he said.

In clinical trials, about half of the patients using the drug experienced loose stools or other gastrointestinal side-effects. However, those effects are less likely to occur with a low-fat diet.

Dieters can use alli for about $2 a day starting this summer. OTC orlistat is not for people who have problems absorbing food or for those who are not overweight, cautioned the FDA.