Metformin for prevention of type 2 diabetes.

OBJECTIVE To evaluate evidence from the medical literature that metformin is effective in preventing type 2 diabetes. DATA SOURCES Primary literature was accessed via a MEDLINE search (1966-December 2003) using the terms metformin, type 2 diabetes, and prevention. DATA SYNTHESIS Two studies evaluated metformin's potential to prevent type 2 diabetes, finding that metformin maintained or reduced fasting blood glucose in non-diabetics. Recently, a large study by the Diabetes Prevention Program showed that metformin may reduce the incidence of diabetes. Researchers compared lifestyle changes, metformin therapy, and placebo groups. They found that both lifestyle changes (58%) and metformin therapy (31%) significantly reduced the occurrence of type 2 diabetes versus placebo. CONCLUSIONS These studies provide evidence that metformin may reduce the occurrence of type 2 diabetes. Because long-term efficacy has not been determined, further studies are needed.