Participants screened through inclusion and exclusion criteria will be randomized to metformin or placebo group (2:1). The information of demographic data, medical history, previous and current medication regimen, and family history regarding psychotic and metabolic diseases will be collected at baseline. The assessments will be carried out at baseline, 12th week and 24th week, including physical examination, anthropometry, blood test(blood routine, liver function, renal function, blood lipids, fasting blood glucose, and serum insulin), electrocardiogram, MRI scan( High-resolution T1-weighted Anatomical Images, Diffusion Tensor Imaging, Resting-state functional MRI and Arterial Spin Labeling) and psychiatry scales(Positive And Negative Syndrome Scale, Scale for Assessment of Negative Symptoms, Calgary Depressing Scale for Schizophrenia, Personal and Social Performance Scale, The Systematic Assessment for Treatment Emergent Events, the Simpson-Angus Extrapyramidal Side Effects Scale and and the Barnes Akathisia Rating Scale); cognitive function will be assessed by the Measurement and Treatment Research to Improve Cognition in Schizophrenia(MATRICS) Consensus Cognitive Battery; biological samples also will be collected and stored to explore related mechanisms.
In this study, the investigators will investigate the effect and the underlying mechanism of metformin treatment on cognitive impairment in individuals with schizophrenia. The study will recruit 120 individuals with schizophrenia at 4 sites, who will be randomized to metformin or placebo group for 24-week treatment. Clinical assessments will be done at screen/baseline, 12th week and 24th week. The specific aims are to compare metformin group versus controls on: 1) cognition; 2) clinical core symptoms. Biological samples also will be collected and stored to explore related mechanisms.