Diabetes mellitus is a widespread disease with many serious chronic complications. An improvement in the oral antidiabetic medication in respect to its mechanism of action and toxicology was needed in order to have effective therapies with high compliance and minimum side effects. In this context, metformin is a widely used oral antidiabetic drug, which, through its mechanism of action, has no risk of hypoglycemia. However, a rare but serious side effect of biguanides is lactic acidosis. This paper presents a number of 13 cases of metformin-associated lactic acidosis, which outline the circumstances triggering the adverse event and the clinical therapeutic measures applied in the poisoned patients. The main situations that favor metformin-associated lactic acidosis are renal impairment and tissue hypoxia, and the intervention is adapted to the particular patient condition and symptoms, such as marked hypotension and cardiac arrest. Although there are commonalities in describing the consulted patients, the final prognosis is not dependent on the dose or metformin plasma levels, but rather on the associated pathologies and medication.