GLP-1, GLP-2, and "GLP-3": Understanding the Incretin Peptide Family

GLP-1 and GLP-2 share a name prefix and a discovery history, but they are structurally distinct hormones acting on entirely different organ systems. Add in "GLP-3" — an informal industry shorthand, not an official hormone designation — and the naming gets genuinely confusing. This article untangles the three.

A Shared Origin, Different Jobs

GLP-1 (glucagon-like peptide-1) and GLP-2 (glucagon-like peptide-2) are both proglucagon-derived peptides — meaning both are produced by cleaving the same precursor protein, proglucagon, in intestinal L-cells. That shared origin is where the similarity ends. GLP-1 acts on metabolic pathways: insulin secretion, appetite regulation, and gastric emptying. GLP-2 acts on the gut itself: it's intestinotrophic, promoting growth of the intestinal mucosa. They bind different receptors (GLP-1R vs GLP-2R) and produce essentially unrelated downstream effects — see what is GLP-2? for the full breakdown of that hormone specifically.

GLP-1: The Metabolic Pathway

GLP-1 receptor agonism is the mechanism behind semaglutide, one of the best-known compounds in the incretin research space. It acts on the GLP-1 receptor to influence insulin secretion, glucagon suppression, and appetite signaling — a single-pathway mechanism, as opposed to the dual- and triple-agonist compounds described below.

"GLP-3": An Informal Shorthand, Not a Real Hormone

There is no naturally occurring hormone called "GLP-3." The term has emerged informally in the research-compound space as shorthand for triple receptor agonists — compounds engineered to activate three metabolic receptors (GLP-1, GIP, and glucagon) in a single molecule, of which retatrutide is the best-known example. See retatrutide explained for the actual pharmacology, and retatrutide vs tirzepatide vs semaglutide for how single-, dual-, and triple-agonist compounds compare. The "GLP-3" label is a naming convenience for a receptor-coverage tier, not a distinct hormone family the way GLP-1 and GLP-2 are.

Why the Naming Confusion Happens

Because GLP-1, GLP-2, and the informal "GLP-3" shorthand all share the same prefix, it's easy to assume they're a simple numbered progression of related hormones — GLP-1, then GLP-2, then GLP-3 as some kind of next generation. They aren't. GLP-1 and GLP-2 are two genuinely distinct, independently discovered proglucagon-derived hormones with different receptors and different organ targets. "GLP-3" isn't a hormone at all — it's industry shorthand describing a class of engineered multi-receptor agonist molecules. Treating all three as points on one continuum is the single most common misunderstanding in this space.

Research Use Only

This article discusses hormone biology and research-compound mechanisms for informational purposes. Nothing here describes a human dosing protocol or therapeutic recommendation. Browse the full catalog or read more in our research library.