GLP-1, GIP and Glucagon Receptors Explained

Multi-agonist research peptides such as Retatrutide are defined by the receptors they engage: GLP-1, GIP, and glucagon. These three belong to the same broad family of metabolic and incretin receptors, and understanding what each does individually makes the interest in compounds that target all three at once much clearer.

The GLP-1 Receptor

GLP-1 (glucagon-like peptide-1) receptors are found in the pancreas and elsewhere, and are among the most extensively studied targets in metabolic research. In laboratory models, GLP-1 receptor activation is associated with glucose-dependent insulin signalling and effects on appetite pathways — which is why single-target GLP-1 agonists were the first generation of compounds in this space.

The GIP Receptor

GIP (glucose-dependent insulinotropic polypeptide) is the other major incretin receptor. It works alongside GLP-1 in the body's response to nutrient intake, and research into dual GLP-1/GIP agonists explores how engaging both pathways simultaneously differs from targeting either alone.

The Glucagon Receptor

The glucagon receptor sits on the opposite side of glucose regulation from insulin signalling, and is additionally involved in energy expenditure pathways. Adding glucagon receptor activity to GLP-1 and GIP is what makes a compound a "triple agonist," and is the specific area of interest in Retatrutide research.

Why Target All Three

Single- and dual-agonist peptides let researchers study one or two of these pathways; triple agonists allow the combined, potentially synergistic engagement of all three within a single molecule to be examined in vitro. For a compound-specific overview, see our primer on Retatrutide and triple agonist peptides.