• Identification of appropriate clinical sites to mount the proposed clinical trial [ Time Frame: Measured pre- and post-treatment ] [ Designated as safety issue: No ]
  
• Feasibility of enrolling a cohort of participants meeting the inclusion and exclusion criteria of the study [ Time Frame: Measured pre- and post-treatment ] [ Designated as safety issue: No ]
  
• Feasibility of protocol implementation with a high level of protocol adherence and low participant attrition [ Time Frame: Measured over 16 weeks of study visits ] [ Designated as safety issue: No ]
  

• Mean difference in body weight between participants assigned to metformin and participants assigned to placebo [ Time Frame: Measured at the last study visit ] [ Designated as safety issue: No ]
  
• Effect of metformin on waist-hip ratio, fasting lipid levels (including total cholesterol, high density lipoprotein [HDL], low density lipoprotein [LDL], triglycerides), fasting glucose, fasting insulin, and hemoglobin A1c [ Time Frame: Measured over 16 weeks of study visits ] [ Designated as safety issue: No ]
  

Schizophrenia is a chronic mental disorder that is characterized, in part, by psychotic symptoms. Psychotic symptoms include hallucinations and delusions, in which a person has abnormal experiences or beliefs, and are commonly treated with antipsychotic medications. Unfortunately, a side effect of many antipsychotics is unwanted weight gain, which can lead to physical illness. Use of the drug metformin has resulted in weight loss among diabetics. Metformin has also been shown to cause weight loss in preliminary studies of people taking atypical antipsychotics—a newer, second generation of antipsychotic medications. Metformin is currently approved by the Food and Drug Administration to treat only people with diabetes. This study will test the usefulness of prescribing metformin as a second medication to treat people with schizophrenia or schizoaffective disorder who are overweight and taking antipsychotics. The study will also provide important feasibility information for future larger studies.

Participation in this study will last 16 weeks. After undergoing baseline assessments, participants will be randomly assigned to receive either metformin or placebo, both of which will be taken twice daily for the duration of the study. All participants will also receive behavioral therapy that will teach them about reducing their weight through diet and exercise. Participants will undergo assessments at 11 study visits: the first 2 will include screening and baseline testing, the next 2 visits will take place after the first and second weeks of receiving treatment, and the last 7 visits will take place every 2 weeks until the end of the study. Assessments will include measurements of body weight, waist-to-hip ratio, and vital signs; clinical interviews about medication adherence, side effects, and alcohol use; and monthly blood tests to assess levels of lipids, glucose, insulin, and hemoglobin A1c.