We will recruit 48 moderately obese men and women seeking weight-loss treatment to participate in a 3-week, randomized, double-blind, cross-over trial of sibutramine 15mg or placebo daily. At the end of weeks 1 and 3, subjects will be asked to participate in a two-day/three-night stay in the Residential Laboratory or Biological Studies Unit of the New York State Psychiatric Institute for comprehensive assessments. The major outcome variable will be the difference in total daily caloric intake between sibutramine and placebo.