There is no GLP-3 receptor. Retatrutide (LY3437943) is a single-chain agonist at three named receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R), and the glucagon receptor (GCGR). The third arm is glucagon, not a third glucagon-like peptide.
That sentence is the whole correction. Catalogs still print “GLP-3” because it is short and it sounds like a series. GIP, GLP-1, GLP-2, then GLP-3. The series is wrong. GLP-1 and GLP-2 are real peptides from the proglucagon system. Glucagon is a different ligand, and its receptor is GCGR, not “GLP-3R.”
This page is nomenclature. It is not a shopping comparison, and it is not a ranking of clinical programs. For the discovery paper and the unimolecular design, see the discovery of retatrutide (LY3437943).
What Coskun actually named
In 2022, Coskun and colleagues at Eli Lilly described LY3437943 in Cell Metabolism as a triple agonist at GCGR, GIPR, and GLP-1R. The title of that paper says “triple glucagon, GIP, and GLP-1 receptor agonist.” It does not invent a GLP-3 receptor. The chemistry is a fatty-acid-acylated peptide engineered from a GIP backbone so that one sequence also signals at GLP-1R and GCGR (doi:10.1016/j.cmet.2022.07.013).
If you need a one-line identity for a lab notebook, that is it: three receptors, three official names, one peptide chain. Catalog slang is optional. The receptor names are not.
GLP-1 and GLP-2 are a real pair. Glucagon is not GLP-3.
Proglucagon is processed into several peptides, including glucagon, GLP-1, and GLP-2. Those three have receptors with official names:
GLP-1R – receptor for glucagon-like peptide-1
GLP-2R – receptor for glucagon-like peptide-2
GCGR – receptor for glucagon
GIPR – receptor for GIP (not a glucagon-like peptide)
IUPHAR/BPS Guide to Pharmacology lists those as distinct class B GPCRs in the glucagon receptor family. GLP-2R is the receptor targeted by teduglutide-class ligands. It is not the third arm of retatrutide. Retatrutide’s third arm is GCGR.
So “GLP-3” as a receptor name fails two tests. It is not how the Coskun paper names the pharmacology, and it is not how receptor nomenclature names glucagon. Calling GCGR “GLP-3R” is like calling the insulin receptor “insulin-like peptide-4 receptor” because the number felt sequential.
Why catalogs still say GLP-3
Research catalogs need a short SKU line. Dual GIP/GLP-1 ligands already trained the market to speak in “GLP plus something.” Adding glucagon as a third letter was easy. “Reta GLP-3” is a commercial nickname for retatrutide. It is not a claim that a GLP-3 receptor exists.
Keep the nickname on the shelf if you need it. Do not copy it into a methods section. A paper, a COA, or a receiving SOP should say retatrutide / LY3437943 and the three receptors, or it should say the sequence and CAS. CAS for retatrutide is 2381089-83-2.
Worked example: what to write instead
If you see
Write this instead
“GLP-3 agonist”
GCGR, GIPR, and GLP-1R agonist (retatrutide / LY3437943), if that is the molecule you mean
“GLP-3 receptor”
There is no such receptor in standard nomenclature. Name GCGR, GLP-1R, GLP-2R, or GIPR.
“Third incretin receptor”
GIP and GLP-1 are incretins. Glucagon is the counter-regulatory hormone at GCGR, not a third incretin.
Catalog line “Reta GLP-3”
Accept as a SKU nickname. Confirm identity on the COA (name, CAS, mass).
What this page is not
It is not an argument that retatrutide is “better” or “worse” than dual agonists. Receptor count is not a ranking. Tirzepatide is a dual GIPR/GLP-1R agonist. Semaglutide-class ligands are GLP-1R agonists. Those are identity statements. They are not outcome claims.
It is also not a claim that every vendor who printed GLP-3 is hiding a different molecule. Most of the time they mean retatrutide. The error is the receptor name, not necessarily the vial. The COA is still the lot record. See how to read a peptide COA.
GLP-3 Is Not a Receptor
There is no GLP-3 receptor. Retatrutide (LY3437943) is a single-chain agonist at three named receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R), and the glucagon receptor (GCGR). The third arm is glucagon, not a third glucagon-like peptide.
That sentence is the whole correction. Catalogs still print “GLP-3” because it is short and it sounds like a series. GIP, GLP-1, GLP-2, then GLP-3. The series is wrong. GLP-1 and GLP-2 are real peptides from the proglucagon system. Glucagon is a different ligand, and its receptor is GCGR, not “GLP-3R.”
This page is nomenclature. It is not a shopping comparison, and it is not a ranking of clinical programs. For the discovery paper and the unimolecular design, see the discovery of retatrutide (LY3437943).
What Coskun actually named
In 2022, Coskun and colleagues at Eli Lilly described LY3437943 in Cell Metabolism as a triple agonist at GCGR, GIPR, and GLP-1R. The title of that paper says “triple glucagon, GIP, and GLP-1 receptor agonist.” It does not invent a GLP-3 receptor. The chemistry is a fatty-acid-acylated peptide engineered from a GIP backbone so that one sequence also signals at GLP-1R and GCGR (doi:10.1016/j.cmet.2022.07.013).
If you need a one-line identity for a lab notebook, that is it: three receptors, three official names, one peptide chain. Catalog slang is optional. The receptor names are not.
GLP-1 and GLP-2 are a real pair. Glucagon is not GLP-3.
Proglucagon is processed into several peptides, including glucagon, GLP-1, and GLP-2. Those three have receptors with official names:
IUPHAR/BPS Guide to Pharmacology lists those as distinct class B GPCRs in the glucagon receptor family. GLP-2R is the receptor targeted by teduglutide-class ligands. It is not the third arm of retatrutide. Retatrutide’s third arm is GCGR.
So “GLP-3” as a receptor name fails two tests. It is not how the Coskun paper names the pharmacology, and it is not how receptor nomenclature names glucagon. Calling GCGR “GLP-3R” is like calling the insulin receptor “insulin-like peptide-4 receptor” because the number felt sequential.
Why catalogs still say GLP-3
Research catalogs need a short SKU line. Dual GIP/GLP-1 ligands already trained the market to speak in “GLP plus something.” Adding glucagon as a third letter was easy. “Reta GLP-3” is a commercial nickname for retatrutide. It is not a claim that a GLP-3 receptor exists.
Keep the nickname on the shelf if you need it. Do not copy it into a methods section. A paper, a COA, or a receiving SOP should say retatrutide / LY3437943 and the three receptors, or it should say the sequence and CAS. CAS for retatrutide is 2381089-83-2.
Worked example: what to write instead
What this page is not
It is not an argument that retatrutide is “better” or “worse” than dual agonists. Receptor count is not a ranking. Tirzepatide is a dual GIPR/GLP-1R agonist. Semaglutide-class ligands are GLP-1R agonists. Those are identity statements. They are not outcome claims.
It is also not a claim that every vendor who printed GLP-3 is hiding a different molecule. Most of the time they mean retatrutide. The error is the receptor name, not necessarily the vial. The COA is still the lot record. See how to read a peptide COA.
Related reading: Discovery of retatrutide (LY3437943) · Retatrutide research overview · GHRH-axis tools are not incretin agonists · Peptide incretin vs non-peptide oral GLP-1
References
For laboratory research only. Not for human or veterinary use. This article is not legal advice and not medical advice.
Last reviewed: 2026-10-15