Exendin-4 is part of a group of peptide hormones, the exendins, which are members of the glucagon superfamily of peptides and are secreted from the Gila monster lizard (Heloderma suspectum) venom gland. Exendins stimulate insulin secretion in response to rising blood glucose levels, and modulate gastric emptying to slow the entry of ingested sugars into the bloodstream. Exendin-4 increases insulin sensitivity and improves glucose tolerance in humans and animals with diabetes. Exendin-4 is currently used for the treatment of type 2 diabetes mellitus in its synthetic form Exenatide.

Exendin-4 shares 53% sequence homology, and certain activities, with glucagon-like-peptide-1 (GLP-1). GLP-1 is produced by enteroendocrine L-cells upon nutrient ingestion and its main role is related to insulin secretion. Unlike GLP-1, exendin-4 is resistant to cleavage by plasma dipeptidyl peptidase IV (DPP-IV), resulting in a longer half-life and duration of action than GLP-1, as well as greater potency in vivo. Exendin-4 binds and activates the glucagon-like peptide-1 receptor (GLP-1R). In addition to its role in insulin sensitivity, exendin-4 also has a role in pancreas development and has anti-cancer properties