 12-month randomized trial with lorcaserin. A total of 136 participants who have lost 5 or more of initial weight in the run-in period will be randomly assigned, in double-blind fashion, to lorcaserin 10 mg BID or matching placebo. To be eligible, participants must have a BMI after prior weight loss 30 kgm2 without co-morbidities or greater than or equal to 27 with a co-morbidity. Randomization will be performed by the Investigational Drug Service at the Hospital of the University of Pennsylvania. Prior to randomization, all participants will complete a second brief history and physical examination, as well as an EKG and blood tests. Medication will be dispensed at the randomization visit and at brief medical visits that follow. Over the 1 year, all participants will participate in 16 group lifestyle modification classes designed for weight loss maintenance, approximately half of which will be delivered by group conference call. 