This study tests the hypothesis that the use of sibutramine, as compared to placebo, will result in a decrease in post-cessation weight gain in overweight and obese individuals who quit smoking, and result in an increase in smoking cessation rates. Participants will be randomly assigned to one of the following two groups: 1) sibutramine plus a behavioral smoking cessation program; or 2) placebo sibutramine plus a behavioral smoking cessation program. Assessments will include post-cessation weight change and smoking cessation rates measured during the study and 9 months following the end of the study.