Differences between groups (MPH vs. placebo) in energy intake and energy expenditure variables, as well as body weight, impulsivity, olfaction, hunger, satiety, and the reinforcing value of food will be evaluated by paired t-tests and repeated measures analyses of variance (ANOVA). Hypotheses of mechanisms linking MPH and reduced food intake and weight loss via reduced food reward will be explored using multiple regression mediational analyses as described by Baron and Kenny.