Last reviewed: September 2026
Quick Answer The short answer to "what is GLP-3" is that it is not a real receptor, hormone, or official drug classification [2]. The name is vendor shorthand, most often applied to retatrutide, a genuine triple agonist of the GLP-1, GIP, and glucagon receptors [1]. This confusion is understandable. GLP-2 is a real hormone with an approved drug behind it [5][6]. That makes "GLP-3" sound like the next entry in a series that stops at two.
Key Takeaways
- Pharmacology references recognize exactly four receptors in the glucagon receptor family: GLP-1R, GIPR, GCGR, and GLP-2R. A GLP-3 receptor appears in none of them [2].
- "GLP-3" is marketplace shorthand, most commonly used for retatrutide (development code LY3437943). The peer-reviewed literature describes retatrutide as an agonist of the GIP, GLP-1, and glucagon receptors [1].
- The published phase 2 trial enrolled 338 adults. At 48 weeks, the 12 mg retatrutide arm lost a mean 24.2% of body weight, against 2.1% on placebo [1].
- Lilly's sponsor-reported phase 3 topline puts the 80-week figure at 28.3% on 12 mg in TRIUMPH-1 [3]. The company plans a biologics license application in the first quarter of 2027 [4].
- GLP-2 is real: a 33-amino-acid hormone derived from pre-proglucagon [2]. Its synthetic analog teduglutide (Gattex) has been FDA-approved for short bowel syndrome since December 21, 2012 [5][6].
- Some catalogs also label tirzepatide "GLP-2." That collides with the real hormone of the same name, which is one more reason to confirm the compound, not the code.
- A certificate of analysis identifies a molecule by analytical testing, never by its catalog name. HPLC reports purity and identity testing confirms the molecule. Matching that identity to the primary literature is the only reliable way to know a compound's reported receptor targets.
Research Use Only. Nothing sold on 99puritypeptides.com is for human or veterinary consumption, and nothing in this article is medical, dosing, or health advice. This page untangles a naming confusion; it does not recommend any compound for any use.
How we graded the evidence. Three rules decided how much weight each claim carries here. Peer-reviewed human trials outrank sponsor press releases, which outrank marketplace listings. A claim about receptor biology needs a pharmacology reference, not a search-result count. And any number carries its population, timepoint, and source, or it does not appear.
Is GLP-3 a Real Receptor?
No, it is not a real receptor. Pharmacology recognizes no receptor by that name, and no hormone called GLP-3 exists either.
A 2024 review in the Journal of Endocrinology states the family plainly [2]. "All four receptors, GLP-1R, GIPR, GCGR, and GLP-2R, belong to the class B1/secretin-like group of G protein-coupled receptors." Four receptors, and the list is exhaustive. Nothing in the pharmacology literature recognizes a fifth member under any spelling.
The numbering explains why the list stops at two. GLP-1 and GLP-2 carry numbers because both are cut from the same precursor protein, pre-proglucagon, alongside glucagon itself [2]. Those numbers track the precursor's products, not generations of drugs. No third GLP is cut from pre-proglucagon, so no GLP-3 was ever named. It does not exist.
Receptor | Gene | Endogenous hormone | Recognized member? | Drug acting on it |
|---|---|---|---|---|
Glucagon receptor | GCGR | Glucagon | Yes | None approved |
GLP-1 receptor | GLP1R | GLP-1 | Yes | Semaglutide, tirzepatide |
GLP-2 receptor | GLP2R | GLP-2 | Yes | Teduglutide (Gattex) |
GIP receptor | GIPR | GIP | Yes | Tirzepatide |
"GLP-3 receptor" | None | None | No | None |
One quiet lesson sits in the drug column. Approved drugs are named for chemistry, not for receptor counts. That is why marketplace shorthand built on counting causes the trouble in the next section.
What Is "GLP-3" Supposed to Be?
In practice, "GLP-3" is a catalog code name, and it almost always means retatrutide.
Retatrutide (development code LY3437943) is described in the peer-reviewed literature as "an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors" [1]. Three receptors share one molecule, so someone counting receptors instead of naming them lands on "GLP-3."
The peer-reviewed literature never uses the term. Search the journals and you find marketplace listings; the papers call retatrutide a GIP/GLP-1/glucagon triple agonist and never a "GLP-3 agonist" [1]. That absence is itself evidence about what kind of name this is.
Catalogs follow a pattern. They had already nicknamed semaglutide "GLP-1" and tirzepatide "GLP-2" on the same receptor-counting logic, so retatrutide became "GLP-3" by succession.
The same arithmetic explains the related mix-up one number down. Tirzepatide engages two receptors, so catalogs call it "GLP-2," which then collides with the genuine gut hormone of that name. "GLP-3" is luckier: it collides with nothing, because no such hormone exists. It only implies one.
Code seen on catalogs | Compound it usually denotes | Receptors engaged | Why the code misleads |
|---|---|---|---|
"GLP-1" variants | Semaglutide | GLP-1R only | Mild: the real hormone shares the name |
"GLP-2" variants | Tirzepatide | GLP-1R and GIPR | Serious: "GLP-2" is also a real, unrelated hormone |
"GLP-3" variants | Retatrutide (LY3437943) | GLP-1R, GIPR, GCGR | Serious: implies a receptor that does not exist |
That middle row is the more dangerous confusion, and it gets its own section next.
Wait, Isn't GLP-2 Real?
Yes, GLP-2 is a real hormone, and that fact is exactly why "GLP-3" sounds plausible.
GLP-2 is a 33-amino-acid peptide cut from pre-proglucagon, like GLP-1 and glucagon. It binds the GLP-2 receptor, found mainly in the gut, where it promotes intestinal growth and nutrient absorption [2].
Its synthetic analog teduglutide, sold as Gattex, is a recombinant analog of human GLP-2 [6]. The FDA approved it on December 21, 2012, for adults with short bowel syndrome dependent on parenteral nutrition [5]. Approval was extended to children aged one year and older in 2019 [6].
Here is the trap. Some research catalogs label tirzepatide "GLP-2" because it engages two receptors. A reader who knows the pharmacology sees "GLP-2" and thinks gut hormone; the catalog means tirzepatide. Same characters, unrelated molecules. "GLP-3" runs the same trick one number higher, except there is no real hormone to collide with, only an empty slot the name invents.
Why Do Vendors Use Code Names Like This At All?
Mostly to avoid trademark trouble, not to deceive anyone about chemistry.
Brand names are trademarked, generic names are clunky, and a catalog needs short labels that survive a spreadsheet. Internal codes solve a boring business problem. A code name is not inherently a red flag, and many sellers use research codes for exactly these unglamorous reasons.
The failure starts when a code borrows the grammar of real pharmacology. "GLP-3" reads as the next numbered hormone because GLP-1 and GLP-2 are real numbered hormones. A code like "RT-77" would confuse nobody; "GLP-3" confuses everyone with a passing knowledge of endocrinology, which is most of the people searching for it.
So judge the code by what backs it. A seller who pairs any code name with a real certificate of analysis, third-party testing, and the actual compound name is running a catalog. One who pairs it with nothing is running a risk. The name on the listing is never the evidence; the documentation behind it is.
This is also why codes persist even when they cause confusion. A short label that a warehouse, a spreadsheet, and a product page can all share has real operational value. Renaming thousands of listings every time a nickname misleads would be its own mess. The workable fix is not to ban code names. It is to make the real compound name impossible to miss wherever the code appears.
So How Do You Actually Know What a Compound Does?
You match the vial's confirmed molecular identity against published literature on that exact molecule. The catalog name is the least reliable part of the package.
Start with the certificate of analysis. Identity testing, usually mass spectrometry, confirms the molecule in the vial matches its reference standard; HPLC quantifies purity and impurities. Then search the confirmed compound name or development code in PubMed. "LY3437943" returns the retatrutide literature instantly. Read the primary characterization rather than a summary.
Our guide to reading a certificate of analysis walks through each line of the document. The certificates page explains what batch documentation should accompany research material.
Line on the CoA | What it establishes | What it cannot establish |
|---|---|---|
Identity (mass spectrometry) | The molecule's mass matches the reference standard | Which receptors it activates |
Purity (HPLC) | The share of the main peak versus impurities | Whether the impurities matter |
Batch or lot number | Traceability to one tested batch | Anything about a different batch |
Third-party lab name | Independent testing occurred | That the methods were validated |
A receptor claim is only as strong as the peer-reviewed paper behind the exact molecule named on that CoA. Everything else is packaging.
Here is a concrete pass. The CoA for a "GLP-3" vial names retatrutide and shows identity confirmation by mass spectrometry with purity by HPLC. Searching PubMed for retatrutide returns the phase 2 paper, whose abstract names the GIP, GLP-1, and glucagon receptors in its first sentence [1]. The catalog name told you nothing; the paper told you everything. That two-minute loop is the whole method.
What the Evidence Does Not Establish
Clearing up a confusion still leaves honest limits. Here they are.
- No pharmacology reference recognizes a GLP-3 receptor, and no peer-reviewed paper uses "GLP-3" as a compound name. The term lives in marketplace listings, not in the literature [2].
- Retatrutide's phase 3 figures are sponsor topline releases from May and July 2026, not peer-reviewed publications. The 28.3% TRIUMPH-1 figure is provisional until the full papers appear [3][4].
- Retatrutide holds no FDA approval for any indication as of September 2026. Lilly has said it plans to file a biologics license application in the first quarter of 2027 [4]. Our guides to FDA-approved peptides and peptide legality track the regulatory picture as it changes.
- Published safety data comes from phase 2. Gastrointestinal events were the most common adverse events: dose-related and mostly mild to moderate, with dose-dependent heart-rate increases peaking at 24 weeks [1]. Longer-term safety beyond the trial windows is not established.
- "GLP-3 side effects" has no independent meaning. The phrase inherits whatever compound the label denotes (usually retatrutide), and no separate GLP-3 safety dataset exists.
Claim in this article | Evidence type | Grade |
|---|---|---|
No GLP-3 receptor exists | Pharmacology review stating the four-member family explicitly | Strong |
Retatrutide engages GLP-1R, GIPR, GCGR | Peer-reviewed phase 2 trial, mechanism in the abstract | Strong |
"GLP-3" is vendor shorthand for retatrutide | Marketplace observation across catalog listings | Pattern, not a trial result |
TRIUMPH-1: 28.3% at 80 weeks | Sponsor topline press release, not peer-reviewed | Provisional |
Teduglutide FDA-approved December 2012 | FDA news release | Strong |
Where Should You Read Next?
The full receptor-by-receptor mechanism table for retatrutide lives in our GLP-1 peptide pipeline guide. That guide also tracks each TRIUMPH phase 3 readout as the data publish. For the head-to-head detail, see our retatrutide versus tirzepatide comparison and the companion piece on how retatrutide differs mechanistically from tirzepatide and semaglutide.
This site's own catalog uses "GLP-3" as a code name. The page at /product/glp-3 covers its retatrutide-class research material, described there as a GLP-1/GIP/glucagon triple-receptor agonist with HPLC purity and identity testing. That code denotes a catalog entry, not a fourth receptor, and batch certificates accompany the material.
References
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526. PMID 37366315. DOI 10.1056/NEJMoa2301972. https://pubmed.ncbi.nlm.nih.gov/37366315/
- Oqua AI, Manchanda Y, McGlone ER, et al. Lipid regulation of the glucagon receptor family. J Endocrinol. 2024;261(3):e230335. PMID 38614123. PMCID PMC11103681. DOI 10.1530/JOE-23-0335. https://journals.bioscientifica.com/joe/article/261/3/e230335/5644/Lipid-regulation-of-the-glucagon-receptor-familyA
- Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Press release. May 21, 2026. https://lilly.mediaroom.com/2026-05-21-Lillys-triple-agonist,-retatrutide,-delivered-powerful-weight-loss-in-pivotal-Phase-3-obesity-trial
- Eli Lilly and Company. Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials, delivering significant improvements in weight and A1C. Press release. July 23, 2026. https://finviz.com/news/371569/lillys-triple-agonist-retatrutide-successful-in-two-additional-phase-3-obesity-trials-delivering-significant-improvements-in-weight-and-a1c
- US Food and Drug Administration. FDA approves Gattex to treat short bowel syndrome. FDA News Release. December 21, 2012. https://www.fiercebiotech.com/biotech/fda-approves-gattex-to-treat-short-bowel-syndrome
- American Pharmaceutical Review. FDA Approves GATTEX for Children with Short Bowel Syndrome. 2019. https://www.americanpharmaceuticalreview.com/1315-News/361021-FDA-Approves-GATTEX-for-Children-with-Short-Bowel-Syndrome/
Frequently Asked Questions
What is GLP-3?
GLP-3 is not a real receptor, hormone, or drug classification. It is a vendor code name, most often applied to retatrutide, a triple agonist of the GLP-1, GIP, and glucagon receptors. Pharmacology references recognize exactly four receptors in this family (GLP-1R, GIPR, GCGR, and GLP-2R) with no fifth member. If you see "GLP-3" on a listing, read it as a catalog label and confirm the actual compound.
Is GLP-3 a real receptor?
No. The glucagon receptor family contains four recognized members: the glucagon receptor, the GLP-1 receptor, the GLP-2 receptor, and the GIP receptor. No GLP-3 receptor appears in pharmacology references, no gene symbol by that name exists, and no hormone called GLP-3 exists. The name is marketplace shorthand that borrows the grammar of real numbered hormones.
Is GLP-3 the same as retatrutide?
In practice, yes: "GLP-3" on a research-chemical listing almost always denotes retatrutide (development code LY3437943). The peer-reviewed literature describes retatrutide as an agonist of the GIP, GLP-1, and glucagon receptors. But "same as" is doing quiet work: the code is not a synonym recognized anywhere in pharmacology, so always confirm the compound name on the certificate of analysis rather than trusting the label.
What is the difference between GLP-1, GLP-2, and GLP-3?
GLP-1 and GLP-2 are real hormones cut from pre-proglucagon, each with its own receptor. GLP-1 regulates insulin and appetite; GLP-2 drives intestinal growth, and its analog teduglutide is an approved drug. "GLP-3" is not a third hormone. It is a vendor nickname, usually for retatrutide, which activates the GLP-1, GIP, and glucagon receptors. Two of these are biology; the third is branding.
Is GLP-2 a real hormone?
Yes. GLP-2 is a 33-amino-acid peptide derived from pre-proglucagon that activates the GLP-2 receptor in the gut, promoting intestinal growth and nutrient absorption. Its synthetic analog teduglutide (Gattex) was FDA-approved on December 21, 2012, for short bowel syndrome. This is precisely why "GLP-3" misleads: it mimics the name of a genuine hormone family member.
Why do some vendors call retatrutide "GLP-3"?
Because retatrutide engages three receptors (GLP-1, GIP, and glucagon), and someone counting receptors wrote "GLP-3". Catalogs had already nicknamed semaglutide "GLP-1" and tirzepatide "GLP-2" on the same receptor-counting logic. The number counts receptors engaged, but it reads as a receptor name, which is where the confusion starts. The peer-reviewed literature never uses the term.
What receptors does retatrutide actually act on?
Retatrutide (LY3437943) is an agonist of three receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor, and the glucagon receptor. All three are class B1 G protein-coupled receptors in the glucagon receptor family. That triple activity is the entire reason the "GLP-3" nickname exists: three receptors, one molecule.
Does "GLP-3" describe a fourth incretin hormone?
No. There are two established incretin hormones, GLP-1 and GIP, plus the related gut hormone GLP-2, and the receptor family holds exactly four members with no fifth entry. "GLP-3" describes no hormone, fourth or otherwise. It is a catalog code that counts the three receptors retatrutide engages and mistakes arithmetic for anatomy.
Are GLP-3 side effects the same as retatrutide side effects?
Yes, because "GLP-3" on a label almost always means retatrutide, so any side-effect list under that name describes retatrutide's reported profile. In the peer-reviewed phase 2 trial, the most common adverse events were gastrointestinal (nausea, diarrhea, vomiting, constipation), dose-related and mostly mild to moderate, with dose-dependent heart-rate increases peaking at 24 weeks. There is no separate "GLP-3" safety dataset.
Is GLP-3 approved by the FDA?
No. There is no FDA-approved product called GLP-3, and retatrutide itself has no FDA approval for any indication as of September 2026. Lilly has said it plans to file a biologics license application in the first quarter of 2027. Our guide to FDA-approved peptides tracks which compounds are actually cleared, and it does not include retatrutide.
Why do peptide vendors use code names instead of the real compound name?
Usually to sidestep trademark issues around brand names, and sometimes for internal catalog consistency. A code name is not automatically a red flag. Many legitimate suppliers use them. The risk is only when the code borrows the grammar of real pharmacology, as "GLP-3" does, implying biology that does not exist. Confirm the compound's identity through its certificate of analysis and the primary literature.
How can I tell what receptor a compound actually targets?
Ignore the catalog name and start with the certificate of analysis: identity testing (usually mass spectrometry) confirms which molecule is in the vial, and HPLC reports its purity. Then search the confirmed compound name or development code (for example, LY3437943) in PubMed and read the primary characterization paper. A receptor claim is only as good as the peer-reviewed paper behind the exact molecule.
Is a vendor code name a red flag by itself?
No. Code names are common in research-chemical catalogs and often exist for trademark reasons rather than to mislead about chemistry. Treat the code as a flag to verify, not a verdict: check that the certificate of analysis names the actual compound, that third-party testing backs it, and that primary literature describes the claimed receptor activity. A code becomes a red flag only when the seller cannot produce that documentation.
What does a certificate of analysis actually identify?
A CoA reports what analytical testing found in a specific batch: identity testing (typically mass spectrometry) confirms the molecule matches its reference standard, and HPLC quantifies purity and impurities. It does not establish what receptors the compound activates, what it does in any organism, or anything about a different batch. Think of it as a chemical ID card, not a pharmacology textbook.
Where can I read the real mechanism data for retatrutide?
Start with the peer-reviewed phase 2 trial: Jastreboff et al., New England Journal of Medicine, 2023, which characterizes retatrutide as a GIP, GLP-1, and glucagon receptor agonist and reports the 48-week results. For the phase 3 TRIUMPH readouts, our GLP-1 peptide pipeline guide tracks each announcement with its source, and our retatrutide comparison pages cover the head-to-head mechanistic detail.
