GLP-3(R) is the research-catalog label for retatrutide (LY3437943), a synthetic peptide studied as a triple agonist at the GIP, GLP-1 and glucagon receptors. There is no GLP-3 hormone. The 3 counts receptors, and the R identifies retatrutide. Amino Foundry lists the compound as GLP-3 with formula C₂₂₁H₃₄₂N₄₆O₆₈, a molecular weight of 4731.33 g/mol, and CAS 2381089-83-2.
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. 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. PubChem indexes the same formula, C221H342N46O68, under CID 171390338. Amino Foundry supplies the compound 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. Research suppliers numbered incretin-class compounds by receptor count: GLP-1 for semaglutide-class single agonists, GLP-2 for the tirzepatide dual agonist, and GLP-3 for the retatrutide triple agonist. The series sorts a catalog well and describes pharmacology badly.
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 naming 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.
How do the GLP-1(S), GLP-2(T) and GLP-3(R) labels compare?
The three labels name three different molecules that share a design logic and differ in receptor count. Molecular weight and CAS number are the identifiers that separate them on a listing, because vendors apply the labels inconsistently. The table below uses the identity references from Amino Foundry's catalog data.
Molecular weight does not rise with receptor count. Tirzepatide is heavier than retatrutide even though it engages one fewer receptor, so a weight near 4,814 Da on a GLP-3 listing is a mislabel, not a variant. Amino Foundry lists GLP-1 (Semaglutide) and GLP-2 alongside the triple agonist.
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, the GLP-1 receptor, and the glucagon receptor. All three signal predominantly through Gs-coupled cyclic AMP production, but they sit in different positions in metabolic control and in different tissues.
The GIP receptor and the GLP-1 receptor are the two incretin receptors, expressed on pancreatic beta cells and in other tissues. The glucagon receptor is expressed most densely in hepatocytes and sits in a counter-regulatory position relative to insulin.
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 that resist cleavage by dipeptidyl peptidase-4 (DPP-4), and a fatty-acid moiety attached through a linker to promote reversible albumin binding. They differ in which receptors the backbone engages.
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. 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 and the stated weight sits near 4731 g/mol.
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.
Where does the TRIUMPH phase 3 program stand as of October 2026?
Retatrutide's phase 3 program runs under the TRIUMPH name, sponsored by Eli Lilly and Company. As of 2026-10-19, ClinicalTrials.gov lists TRIUMPH-1 through TRIUMPH-4 as completed and TRIUMPH-5 through TRIUMPH-9 as active, not recruiting. These are registry and company statements, reported here as facts, not guidance.
Trial
Registry ID
Population (as registered)
Enrollment
Status (Oct 2026)
TRIUMPH-1
NCT05929066
Obesity or overweight
2,335
Completed
TRIUMPH-2
NCT05929079
Type 2 diabetes with obesity or overweight
1,152
Completed
TRIUMPH-3
NCT05882045
Obesity and cardiovascular disease
1,946
Completed
TRIUMPH-4
NCT05931367
Obesity or overweight with knee osteoarthritis
445
Completed
TRIUMPH-5
NCT06662383
Comparison with tirzepatide
800
Active, not recruiting
Lilly announced TRIUMPH-1 topline results on 2026-05-21 and TRIUMPH-2 and TRIUMPH-3 topline results on 2026-07-23, with a biologics license application submission planned for the first quarter of 2027, as reported by Pharmacy Times on 2026-07-24. TRIUMPH-2 was presented at the EASD 2026 meeting in Milan on 2026-09-30 alongside Lancet-journal publications, as noted by ConscienHealth, and full TRIUMPH-1 results appeared in the New England Journal of Medicine on 2026-09-29. Retatrutide remains investigational, and none of this applies to research-grade material.
How should researchers verify a GLP-3R listing?
Three checks resolve most listing confusion: the CAS number, the formula and molecular weight, and the observed mass on the Certificate of Analysis. The first two confirm the listing describes retatrutide; only the third confirms that the material in the vial matches the listing.
First, the CAS number should read 2381089-83-2. Second, the molecular weight should be stated near 4731 g/mol 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, and the peptide purity guide covers what the HPLC number does and does not measure.
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, hepatocyte, and adipocyte models for concurrent signal transduction at three receptors, with published work examining cAMP responses, receptor internalization, and downstream pathway activation. The research-grade material sold under the GLP-3R label is intended for in vitro and analytical work only.
The clinical program registered under LY3437943 has reported phase 2 results and the phase 3 TRIUMPH readouts summarized above. Those trials are the source of the published human data on the compound and are covered in the retatrutide research overview linked above. Research-grade GLP-3R is used to characterize 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.
Reference
Common questions
GLP-3(R) is a research-catalog label for retatrutide, the Eli Lilly compound coded LY3437943. It is a synthetic peptide studied as a triple agonist at the GIP, GLP-1 and glucagon receptors. There is no endogenous hormone called GLP-3; the number counts receptors, and the R identifies retatrutide.
No. The proglucagon gene encodes GLP-1 and GLP-2, both real hormones with their own receptors, but no GLP-3. The research market adopted GLP-1, GLP-2 and GLP-3 as shorthand for single, dual and triple agonists, so GLP-3 is a catalog convention that points to retatrutide rather than a hormone.
The three labels map to three different molecules. GLP-1(S) is semaglutide, a single GLP-1 receptor agonist. GLP-2(T) is tirzepatide, a dual GIP and GLP-1 receptor agonist. GLP-3(R) is retatrutide, which adds glucagon receptor activity for three targets. CAS number and molecular weight distinguish them reliably.
As of October 2026, ClinicalTrials.gov lists TRIUMPH-1, -2, -3 and -4 as completed and TRIUMPH-5 through -9 as active. TRIUMPH-2 was presented at EASD 2026 on September 30, and Lilly has stated that a biologics license application submission is planned for the first quarter of 2027.
Cited literature
References
Primary literature and public databases referenced above. Each link resolves on the publisher or database of record.
