Diabetes mellitus (DM) is characterised by an absolute or relative deficiency of insulin. There are currently eight different pharmacological classes of anti-diabetic agents. These include agents that increase insulin secretion, improve insulin action and delay carbohydrate absorption. The classes of anti-diabetic agents are sulphonylureas, meglitinides, biguanides, thiazolidinediones, α-glucosidase inhibitors, GLP-1 (glucagon-like peptide-1) receptor agonists, DPP-4 (dipeptidyl peptidase-4) inhibitors and synthetic amylin analogues. Sulphonylureas are known as insulin secretagogues as their major mechanism of action is to increase insulin secretion. The glinides are newer insulin secretagogues that include the meglitinide, repaglinide, and a benzoic acid derivative, and the amino acid derivative, nateglinide. Metformin and phenformin were introduced for the therapy of DM in the 1950s. Thiazolidinediones (TZDs), like metformin, belong to the class of drugs known as insulin sensitisers. Incretins are gut-derived peptides secreted in response to meals, specifically the presence and absorption of nutrients in the intestinal lumen.