[Metformin: new data for an old molecule].

Metformin is the first-line oral agent for the treatment of type 2 diabetes according to the guidelines. Metformin decreases hepatic glucose production, does not induce weight gain and does not increase the risk of hypoglycemia. However, decades after its introduction, its mode of action has been only recently highlighted. The side effects of metformin are well known and consist primarily of digestive problems. Although rare, the dreaded complication is lactic acidosis, which can develop in patients with severe renal insufficiency or in conditions of low perfusion. The purpose of this article is to review the indications, risks and benefits of this drug, but also to discuss new evidence related to its mechanism of action and the conditions that increase the risk of lactic acidosis.