Can Metformin Reduce Type 2 Diabetes Risk?

A study evaluated the efficacy of metformin to prevent or delay the onset of type 2 diabetes as well as any associated complications in high-risk patients. The researchers queried the Cochrane Central Register of Controlled Trials; Medlne; Scopus; ClinicalTrials.gov; the World Health Organization International Clinical Trials Registry Platform; and the reference lists of systematic reviews, articles, and health technology assessment reports through March 2019. Eligible studies were randomized, controlled trials (RCTs) with a duration of at least one year that compared metformin to any pharmacological glucose-lowering intervention, behavior-changing intervention, placebo, or standard care in patients with impaired glucose tolerance or fasting glucose, moderately elevated glycosylated hemoglobin A1c (HbA1c), or a combination of the aforementioned conditions. Final analysis included 20 RCTs with 6,774 total patients (data on 48% of patients were obtained from a single trial). Trial lengths ranged from one to five years. Moderate-quality evidence supported the finding that metformin, compared with placebo or diet and exercise, reduced or delayed the risk of type 2 diabetes in high-risk patients. Also with moderate-quality evidence, the researchers observed no difference between metformin versus intensive diet and exercise in reduced or delayed risk of type 2 diabetes. Combined metformin and intensive diet and exercise, compared with intensive diet and exercise, was neither advantageous nor disadvantageous in type 2 diabetes development; this was observed with very low-quality evidence. Data were sparse or unavailable on mortality, macrovascular and microvascular diabetic complications, and health‐related quality of life.