Incretin is a group of metabolic hormones that are released after eating and stimulate a decrease in blood glucose levels. They augment the secretion of insulin released from pancreatic beta cells of the islets of Langerhans and inhibit glucagon release from the alpha cells of the islets of Langerhans. In addition, they slow the rate of absorption of nutrients into the bloodstream by reducing gastric emptying and may directly reduce food intake. The two main candidate peptides that fulfill criteria for an incretin are the intestinal peptides glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP). The incretin effect describes the phenomenon whereby oral glucose intake elicits a higher insulin response compared to intravenously introduced glucose that produces the same levels of serum glucose levels. Incretin hormones have an important role physiologically, namely they are involved in the pathophysiology of obesity and type 2 diabetes, and they have therapeutic potential that can be traced to well-characterized physiological effects. Medicines called incretin-based treatments are now available to control post-meal glucagon and help reduce post-meal blood sugars.