Participation in this study will be divided into two phases lasting a total of 40 weeks. Phase 1 will last 16 weeks and include baseline testing and seven scheduled study visits. During this phase, participants will be randomly assigned to receive either sertraline and metformin or sertraline and placebo on a daily basis. The baseline visit will include the following tests and measures: an electrocardiogram (EKG), which will measure the electrical activity in the heart; an oral glucose tolerance test (OGTT), which will measure how a person's body breaks down glucose; a blood test, which will measure lipids, hemoglobin A1C, and other cardiometabolic risk factors; a dual energy x-ray absorptimetry (DEXA) scan, which will measure body fat; a pregnancy test for women; measurements of vital signs, height, weight, waist-to-hip ratio, and waist circumference; and questionnaires concerning health, medication use, physical activity, diet, and mood. Some of the questionnaires will be administered through interviews with a researcher. During the study visits, which will occur every 2 weeks, participants will complete questionnaires, unused medication will be collected, and new medication will be handed out. At Week 8, participants will provide an additional blood sample by finger stick. At the end of Phase 1, participants will undergo repeat baseline testing.