What is the difference between GLP-1 and GLP-3?

GLP-1 is a natural gut hormone with its own receptor. GLP-3 is not a hormone: it is an informal label for retatrutide, a drug that activates the GIP, GLP-1 and glucagon receptors.

Is there a GLP-3 hormone?

No. The proglucagon precursor yields GLP-1 and GLP-2 but no GLP-3, and no GLP-3 receptor gene exists. Eli Lilly calls the term scientifically inaccurate.

GLP-2 is a 33-residue gut hormone from proglucagon that acts on the GLP-2 receptor, mainly in the intestine. Its approved analogue, teduglutide (Gattex), is used for short bowel syndrome.

Is tirzepatide a GLP-2?

No. Tirzepatide activates the GIP and GLP-1 receptors and has no GLP-2 receptor activity. Labels like "GLP-2 T" refer to its two receptors, not to the GLP-2 hormone.

What does GLP-3 RT mean?

GLP-3 RT (and GLP-3 R, GLP-3 Reta) is a catalogue name for retatrutide (LY3437943), Eli Lilly's investigational triple receptor agonist.

What do glp1, glp2 and glp3 have in common?

In shop labels, the number roughly counts the receptors a drug activates: one for semaglutide, two for tirzepatide, three for retatrutide. Only GLP-1 and GLP-2 are also real hormones.

GLP-1 vs GLP-2 vs GLP-3: What the Names Mean

GLP-1 and GLP-2 are real hormones; GLP-3 is not. Glucagon-like peptide-1 and glucagon-like peptide-2 are both cut from the proglucagon precursor and each has its own receptor. “GLP-3” is an informal shop label for retatrutide, a drug that hits three receptors. In the same shorthand, “GLP-2” is often used for tirzepatide, which has nothing to do with the GLP-2 hormone.

GLP-1 vs GLP-2 vs “GLP-3” at a glance

	GLP-1	GLP-2	“GLP-3”
Is it a natural hormone?	Yes	Yes	No
Where it comes from	Proglucagon, cleaved in intestinal L-cells	Proglucagon, cleaved in intestinal L-cells	A market label, not a molecule
Length	30–31 residues (GLP-1(7-36) amide / (7-37))	33 residues	n/a
Its receptor	GLP-1 receptor (GLP1R)	GLP-2 receptor (GLP2R), mainly in the gut	No GLP-3 receptor exists
Main research area	Insulin secretion, glucagon suppression, gastric emptying, appetite	Intestinal mucosal growth and nutrient absorption	n/a
Approved drug based on it	Semaglutide and other GLP-1 receptor agonists	Teduglutide (Gattex), for short bowel syndrome	None
What shops sell under this name	Semaglutide (“GLP-1 S”)	Tirzepatide (“GLP-2 T”, “GLP-2 Tirz”, “GLP-2 TZ”)	Retatrutide (“GLP-3 R”, “GLP-3 RT”, “GLP-3 Reta”)

Sources: UniProt P01275 (proglucagon); HGNC glucagon receptor family; Gattex (teduglutide) label; Eli Lilly on retatrutide.

What GLP-1 is

Glucagon-like peptide-1 is released from enteroendocrine L-cells in the gut after a meal. It increases glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying and reduces food intake, acting through the GLP-1 receptor. The proglucagon gene that encodes it also encodes glucagon, GLP-2, oxyntomodulin and glicentin. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Drucker DJ. Cell Metabolism, 2018; Sandoval DA, et al. Physiological Reviews, 2015.

Semaglutide is a 31-residue GLP-1 analogue (two substitutions plus a C18 fatty diacid) and a selective GLP-1 receptor agonist: it acts on that one receptor only.

What GLP-2 is

Glucagon-like peptide-2 is a 33-residue peptide released from the same L-cells. Its receptor, GLP2R, is found mainly in the gastrointestinal tract, and its actions are on the gut itself: mucosal growth, nutrient absorption and mesenteric blood flow. The approved GLP-2 analogue, teduglutide (Gattex), is used in short bowel syndrome, not in metabolic disease. Physiology and pharmacology of the enteroendocrine hormone glucagon-like peptide-2. Drucker DJ, et al. Annual Review of Physiology, 2014.

So what is “GLP-3”?

There is no GLP-3. UniProt’s list of proglucagon products contains no such peptide, and the HGNC gene database lists only two “GLP” receptor genes, GLP1R and GLP2R. The name is used for retatrutide, Eli Lilly’s investigational agonist of three receptors: GIP, GLP-1 and glucagon. Lilly describes “GLP-3” as a scientifically inaccurate label used informally for triple hormone receptor agonists, and prefers “triple agonist”.

And “GLP-2” for tirzepatide?

This is the most misleading of the three labels. Tirzepatide activates the GIP and GLP-1 receptors, two receptors, which is presumably where the “2” comes from. It has no GLP-2 receptor activity and is not related to the GLP-2 hormone. Some shops even title tirzepatide “GLP-2” outright. If you mean the gut hormone or its analogue teduglutide, “GLP-2” is the right name; if you mean tirzepatide, it is not.

The real ladder: one, two, three receptors

Compound	Shop label	Receptors	Length	Status
Semaglutide	GLP-1 S	GLP-1R	31 residues	FDA-approved (Ozempic, Wegovy, Rybelsus)
Tirzepatide	GLP-2 T / GLP-2 Tirz	GIPR + GLP-1R	39 residues	FDA-approved (Mounjaro, Zepbound)
Retatrutide	GLP-3 R / GLP-3 RT / GLP-3 Reta	GIPR + GLP-1R + GCGR	39 residues	Investigational (phase 3)
Survodutide	—	GLP-1R + GCGR	Peptide	Investigational

Read that way, the numbers in the shop labels roughly count receptors, not hormones. That is the most useful thing to remember about them: a “GLP-3” product is not a third member of a hormone family, it is a multi-receptor drug.

For the molecules side by side, see retatrutide vs tirzepatide, retatrutide vs semaglutide and tirzepatide vs semaglutide.

What we stock under these names

Clean Peptide sells GLP-3 Reta (retatrutide), GLP-2 Tirz (tirzepatide) and survodutide as laboratory reference materials. Each product page names the compound, gives its identity data and shows the certificate for every size. We do not sell semaglutide at the moment.