GLP-3R is a research-market listing label for retatrutide, a synthetic single-chain peptide studied as a triple agonist at the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor. There is no endogenous hormone called GLP-3. The label was adopted by research suppliers to place the compound in a numbered series alongside the earlier GLP-1 and GLP-2 market labels, and the trailing R identifies retatrutide specifically. Amino Foundry lists the compound as GLP-3 with the molecular formula C₂₂₁H₃₄₂N₄₆O₆₈, a molecular weight of 4731.33 Da, and CAS number 2381089-83-2. It is supplied as a lyophilized powder at 99%+ HPLC purity for laboratory research only.
Searches for "what is GLP-3R" and "amino GLP3" are usually researchers encountering the label for the first time and trying to map it back to a compound in the published literature. The mapping is: GLP-3R equals retatrutide equals LY3437943, the Eli Lilly development code under which the phase 1, phase 2, and phase 3 trials are registered.
Why is retatrutide called GLP-3 when there is no GLP-3 hormone?
The "3" refers to three receptors, not a third glucagon-like peptide. The proglucagon gene encodes several peptides, and two of them carry the glucagon-like peptide name: GLP-1, an incretin released from intestinal L-cells, and GLP-2, an intestinotrophic peptide co-secreted with it. Both are real hormones with well-characterized receptors. There is no GLP-3 in the proglucagon-derived family.
The research market's numbering series emerged as a shorthand for compound generations. GLP-1 became the label for semaglutide-class single agonists. GLP-2 was applied to tirzepatide, a dual GIP/GLP-1 agonist, because it engaged two receptors, even though the actual GLP-2 hormone has nothing to do with tirzepatide. GLP-3 then followed for retatrutide because it engages three. The naming is convenient for catalog organization and misleading for pharmacology, and it collides with real hormone nomenclature at the GLP-2 step. Teduglutide, for instance, is a genuine GLP-2 receptor agonist studied in intestinal epithelial models, and a researcher searching for GLP-2 analogs will encounter tirzepatide listings that have no relationship to that receptor.
The compliance note on the Amino Foundry catalog draws the line explicitly: GLP-2 as a market label means tirzepatide, GLP-3 as a market label means retatrutide, and neither should be conflated with the hormones of the same name.
What receptors does GLP-3R (retatrutide) act on?
Published pharmacology characterizes retatrutide as an agonist at three class B G-protein-coupled receptors. The GIP receptor and the GLP-1 receptor are the two incretin receptors, expressed on pancreatic beta cells and in other tissues, and both signal predominantly through Gs-coupled cyclic AMP production. The glucagon receptor is expressed most densely in hepatocytes and also signals through Gs and cAMP, but sits in a counter-regulatory position relative to insulin in metabolic control.
In vitro characterization reported by the developing group described the compound's relative potency at the three receptors as imbalanced by design, with GIP receptor activity comparatively strong, GLP-1 receptor activity lower than that of native GLP-1, and glucagon receptor activity intermediate. That ratio is a deliberate feature of the molecule and one of the reasons it is studied as a distinct compound rather than as a variant of dual agonists. The retatrutide research overview covers the receptor pharmacology in more depth, and the GLP-1 receptor agonists article covers the single-target class it is most often compared against.
How does the GLP-3R structure differ from GLP-1 and GLP-2 analogs?
All three market-label compounds share a design logic: a peptide backbone related to the native glucagon-family sequences, non-natural amino acid substitutions to resist enzymatic cleavage by dipeptidyl peptidase-4 (DPP-4), and a fatty-acid moiety attached through a linker to promote reversible albumin binding and extend circulating half-life. Where they differ is in which receptors the backbone has been engineered to engage.
Semaglutide (the GLP-1 market label) is a GLP-1 backbone with a C18 fatty di-acid at lysine 26. Tirzepatide (the GLP-2 market label) is built on a GIP backbone with substitutions that add GLP-1 receptor activity, with a C20 fatty di-acid at lysine 20. Retatrutide (GLP-3R) extends the approach to include glucagon receptor activity while retaining the GIP and GLP-1 engagement, and carries its own lipidation. The molecular weight increases along the series, from roughly 4,114 Da for semaglutide to 4,731 Da for retatrutide, reflecting the longer backbone and the lipid moiety. Amino Foundry does not publish a full sequence for the GLP-3 listing because the compound's sequence is proprietary to the developer; the formula, molecular weight, and CAS number are the identity references available.
What does the R in GLP-3R stand for?
The R stands for retatrutide. Some vendors list the compound as GLP-3, some as GLP-3R, some as GLP-3 (Retatrutide), and some simply as retatrutide. These are all the same molecule when the CAS number matches 2381089-83-2. The R suffix was introduced to disambiguate as other triple agonists entered development, since a future triple agonist from a different developer could also be marketed as GLP-3 under the numbering convention.
A related ambiguity appears in the GLP-1 series, where suffixes like GLP-1S (semaglutide) and GLP-1T (tirzepatide, sometimes listed under GLP-2 instead) are used inconsistently across suppliers. The reliable identifier is always the CAS number and the molecular weight, not the label.
How should researchers verify a GLP-3R listing?
Three checks resolve most listing confusion. First, the CAS number should read 2381089-83-2. Second, the molecular weight should be stated near 4731 Da and the formula as C₂₂₁H₃₄₂N₄₆O₆₈; a listing that gives tirzepatide's weight (near 4,814 Da) or semaglutide's (near 4,114 Da) under a GLP-3 label is mislabeled. Third, the Certificate of Analysis should show an observed mass from mass spectrometry that matches the theoretical value, which is the only test that confirms identity rather than purity. The COA reading guide walks through where to find each of these on the document.
Listings that describe GLP-3 as a "third generation GLP-1" or "the successor to GLP-2" are using marketing language for a pharmacological distinction. The compound is not a GLP-1 analog with improved properties; it is a differently targeted molecule that happens to include GLP-1 receptor activity among its three targets.
What is GLP-3R studied for in research?
Retatrutide is studied in pancreatic beta-cell models, hepatocyte models, and adipocyte models for concurrent signal transduction at the three receptors, with published work examining cAMP responses, receptor internalization, and downstream metabolic pathway activation. The clinical program registered under LY3437943 has reported phase 2 results in adults with obesity and in adults with type 2 diabetes, and phase 3 results from the TRIUMPH program began reporting in late 2025 and through 2026. Those trials are the source of the published human data on the compound and are summarized in the retatrutide research overview linked above.
The research-grade material sold under the GLP-3R label is intended for in vitro and laboratory work characterizing the compound's receptor pharmacology, stability, and analytical profile. It is not a pharmaceutical product.
All compounds referenced in this article, including GLP-3 (retatrutide), are supplied for research purposes only and are not for human use. Nothing here describes or endorses any use outside laboratory research. These products are not intended to diagnose, treat, cure, or prevent any disease.
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