Metformin (MET) is the first-line agent in treatment of type 2 diabetes. However, MET has been associated with lactic acidosis (MALA), a potential but rare complication which has influenced treatment strategies in decades. Recently, guidelines have been changed in regards of age and heart failure and the contradiction of chronic renal impairment has been debated. This article identifies potential risk groups and situations that would benefit from a temporary interruption in the MET treatment.