Lactic acidosis is the most important and life-threatening side effect of metformin that is widely used in the treatment of type 2 diabetes mellitus. In this case report, two cases who were treated in our intensive care unit for lactic acidosis due to high-dose metformin intake for suicidal purposes are presented. The first patient could be successfully treated with continuous venous-venous hemodiafiltration (CVVHDF) and supportive therapy. The second case required endotracheal intubation and mechanical ventilation in addition to CVVHDF and supportive therapy due to delay in treatment.