This study will determine whether the drug metformin improves the effects of traditional antidepressant medications in people who are overweight.

Current depression treatments are not effective for approximately one-half of overweight people, and depression eventually returns in approximately one-third of those overweight people whose initial treatment is effective. One possible reason for these treatment failures is that overweight people often experience a condition called insulin resistance (IR), which can lead to type 2 diabetes, an associated disease that might also affect depression treatment. IR results in elevated blood sugar levels that may interfere with medications used to treat depression. Metformin, a medication commonly used to treat diabetes, reduces blood sugar levels. This study will examine whether taking metformin with the antidepressant medication sertraline will enhance the effectiveness of sertraline in people who are overweight and depressed.

Participation in this study will last a total of 16 weeks and will include baseline testing and ten scheduled study visits. 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, glycosylated 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.

Inclusion Criteria:

• Body mass index (BMI) greater than 28.7
• Positive screening for depression
• Must live within 100 miles of the St. Louis metropolitan area

Exclusion Criteria:

• Pregnant or breastfeeding
• Known hypersensitivity to sertraline or metformin
• Recent history of heart attack or unstable heart disease
• Severe liver disease or kidney impairment, defined by a serum creatine level above 3 mg/dL
• Psychiatric disorder thought to affect management, such as schizophrenia, or alcohol or drug dependence

16 weeks