Diabetes mellitus is a chronic disease that is growing in prevalence worldwide. Pharmacologic therapy is often necessary to achieve optimal glycemic control in the management of diabetes. Today's clinicians are presented with an extensive range of oral antidiabetic drugs for type 2 diabetes. These main drug classes include agents that stimulate insulin secretion (sulphonylureas and rapid-acting secretagogues), reduce hepatic glu-cose production (biguanides), delay digestion and absorption of intestinal carbohydrate (α-glucosidase inhibitors) or improve insulin action (thiazolidinediones). We review the mechanism of action, efficacy and side effects of the different classes of oral antidiabetic drugs and discuss the current recommendations for their use.