“GLP-3” is not a real hormone. It’s an internet nickname for retatrutide, Eli Lilly’s experimental drug that activates three receptors (GLP-1, GIP and glucagon). People counted the receptors and called it “GLP-3”. Biologically, though, the “1” in GLP-1 is part of a hormone’s name, not a count. Your body makes GLP-1 and GLP-2. It does not make a GLP-3.
“RT3”, “Reta”, “R3”, “r3ta” and even “ratatouille” are all names for the same molecule, whose official code is LY3437943. Sellers and influencers lean on code names partly to slip past social-media filters that block the real name.
Because the names are fuzzy, the only way to know a vial actually holds retatrutide is identity testing. Mass spectrometry should show a molecular weight of about 4,731 Da (formula C221H342N46O68). The label alone won’t tell you.
Is GLP-3 real? (No, and here’s why)
If you googled “what is GLP-3”, you may have expected to read about a new hormone that comes after GLP-1. There isn’t one.
“GLP” stands for glucagon-like peptide. Your body makes these peptides by cutting up one larger precursor protein called proglucagon. How it’s cut depends on where it’s made:[4]
- In the pancreas (alpha cells), proglucagon is processed into glucagon, the hormone that raises blood sugar.
- In the gut (intestinal L-cells), the same precursor is processed into GLP-1, GLP-2, glicentin and oxyntomodulin.
GLP-1 and GLP-2 got their numbers because they’re two different glucagon-like stretches within the same precursor. The numbers are names, not counts of how many receptors something hits. No third glucagon-like peptide called GLP-3 is produced from proglucagon.[4] So when someone says “GLP-3”, they don’t mean a hormone at all. They mean a drug.
Why retatrutide got called “GLP-3”
The drug behind the nickname is retatrutide (LY3437943). It’s a single engineered peptide that activates three different receptors:[1]
- The GLP-1 receptor, the same target as semaglutide (Ozempic, Wegovy).
- The GIP receptor. GIP is a different gut hormone, glucose-dependent insulinotropic polypeptide.
- The glucagon receptor.
Online shorthand went like this: semaglutide hits one receptor, so “GLP-1”. Tirzepatide hits two, so people started calling it “GLP-2”. Retatrutide hits three, so “GLP-3”. It’s catchy, but it’s wrong on two counts:
- Only one of retatrutide’s three targets is a GLP receptor. GIP and glucagon aren’t GLPs.
- “GLP-2” is already the name of a real hormone with its own approved drug, which creates real confusion (more below).
The scientific name for what retatrutide does is triple hormone receptor agonist, sometimes shortened to “triple agonist” or, in press coverage, “triple G” (GIP, GLP-1, glucagon).
How strongly does it hit each receptor?
The three activities aren’t equal. In Lilly’s discovery paper, retatrutide showed balanced activity at the glucagon and GLP-1 receptors and stronger activity at the GIP receptor.[1] A reference-standard supplier reports cell-assay EC50 values of about 0.064 nM at the GIP receptor, 0.78 nM at GLP-1 and 5.8 nM at glucagon, measured in engineered human cell lines.[8] A lower number means it takes less compound to switch the receptor on. So if anything, retatrutide is a “GIP-first” molecule, which is another reason “GLP-3” is a misleading label.
The molecule is lipidated (a fatty diacid chain is attached through a linker). This lets it bind to albumin in the blood, which is why it lasts long enough for once-weekly use in trials. Its half-life in the phase 1b study was about 6 days.[2] For the full background, see What is retatrutide?
Every name for retatrutide, decoded
Here’s the decoder ring. All of these refer to the same compound, or at least they’re supposed to.
| Name you’ll see | What it is | Where it comes from |
|---|---|---|
| Retatrutide | Official nonproprietary (generic) name | Adopted name (USAN)[6]; used in trial publications[3] |
| LY3437943 (LY-3437943) | Lilly’s development code | “LY” is Lilly’s compound prefix; used in early papers[1][2] |
| CAS 2381089-83-2 | Chemical registry number | Chemical Abstracts Service; shown on reference-standard data sheets[6] |
| GLP-3 | Informal nickname | Counting the three receptors; social media and vendor listings[10] |
| r3ta, ratatouille | Slang / filter-dodging spellings | Social media[10] |
| Reta, R3, RT3, RT-3 | Shorthand and vendor product codes | Forums and supplier catalogues (TrueLabs lists it as “RT3 (Retatrutide)”) |
| Triple agonist, triple G | Description of its mechanism | Scientific and press shorthand |
| Brand name | None yet | Retatrutide isn’t approved, so it has no trade name |
That last row matters. Approved drugs have brand names (Ozempic, Wegovy, Mounjaro, Zepbound) as well as generic names. Retatrutide has only its generic name and its code. Anything sold under a brand-sounding name is a seller’s invention, not Lilly’s.
Why vendors use code names
If the molecule has a perfectly good name, why all the codes? A few reasons, some more legitimate than others.
1. Getting past platform filters
Public Citizen’s June 2026 report on retatrutide describes slang like “ratatouille”, “r3ta” and “GLP-3” that “helps evade the social media filters that block mention of the substance’s real name.”[10] Social platforms, ad networks and payment processors increasingly flag the names of prescription and unapproved drugs, and code names are an attempt to get around them.
2. Pressure from the drug’s developer
Lilly has been aggressive about unapproved retatrutide. In August 2026 it filed six lawsuits against US businesses it accused of illegally selling black-market retatrutide. It said it had referred more than 200 individuals and entities to regulators and law enforcement, and its chief medical officer called the black-market product “entirely unverified.”[11] Lilly also asked social-media and e-commerce platforms, payment processors and shippers to cut off illegal sellers.[11] More pressure on the real name means more incentive to use codes.
3. Catalogue shorthand
Not every code is sneaky. Labs and suppliers use short product codes all the time, the way a hardware store has SKUs. The question to ask is not “does this seller use a code?” but “does this seller tell me, in plain text, which molecule the code stands for, and prove it with a batch-specific test?” A product page that says “RT3 (Retatrutide)” and publishes identity data is transparent. A listing that only says “GLP-3” and never names the compound is not.
A code name does not change what a product legally is. Health Canada’s April 2026 advisory names retatrutide among unauthorized peptides, and it states that “For Research Use Only” labelling does not exempt a product from regulation.[12] Calling it “GLP-3” doesn’t change that.
GLP-1, GLP-2 and “GLP-2T”: the related names
The GLP nicknames overlap with real hormones and real drugs, so it’s worth sorting them out.
GLP-1: a real hormone, and a real drug class
GLP-1 is made in the gut after meals.[4] “GLP-1 drugs” (GLP-1 receptor agonists) include semaglutide (Ozempic, Wegovy, Rybelsus) and others. When people say “a GLP-1”, they usually mean one of these medicines. See Retatrutide vs Ozempic for how the one-receptor and three-receptor drugs compare.
GLP-2: a real hormone with a real (and unrelated) drug
GLP-2 is also made by intestinal L-cells. Its main job is to maintain and expand the lining of the gut and help absorb nutrients.[5] It has nothing to do with weight loss. Its drug version is teduglutide, sold in Canada as Revestive. Health Canada authorized it on September 4, 2015 for adults with short bowel syndrome who depend on intravenous nutrition, and in 2019 extended it to children 1 year and older.[5] Teduglutide differs from natural GLP-2 by a single amino acid, which makes it resist breakdown and last longer.[5]
“GLP-2”, “GLP-2T”, “GLP-2TZ”: tirzepatide nicknames
Following the same counting logic, some sellers list tirzepatide (Mounjaro, Zepbound), a dual GLP-1/GIP agonist, as “GLP-2”, “GLP-2T”, “GLP-2TZ” or “GLP-2 Tirz”. That collides head-on with the real GLP-2 hormone and teduglutide, so it’s the most confusing nickname in the family. If a listing says “GLP-2”, the only way to know what it means is the named compound and its identity test. More on tirzepatide in our tirzepatide research guide.
Quick reference: the whole family
| Name | Real hormone? | What it usually refers to | Receptors hit |
|---|---|---|---|
| GLP-1 | Yes | The hormone, or GLP-1 drugs like semaglutide | GLP-1 |
| GLP-2 | Yes | The gut-lining hormone; teduglutide (Revestive). Also misused for tirzepatide | GLP-2 (hormone/teduglutide); GLP-1 + GIP (tirzepatide) |
| “GLP-2T” / “GLP-2TZ” | No | Tirzepatide nickname | GLP-1 + GIP |
| “GLP-3” | No | Retatrutide nickname | GLP-1 + GIP + glucagon |
| GIP | Yes | Gut hormone; one of tirzepatide’s and retatrutide’s targets | GIP |
| Glucagon | Yes | Pancreatic hormone; one of retatrutide’s targets | Glucagon |
How to confirm a vial is actually retatrutide
Names can be anything. Molecules can’t. A real retatrutide sample has a specific chemical formula and mass, and that’s what an identity test checks.
The numbers to know
| Property | Retatrutide | Source |
|---|---|---|
| Molecular formula | C221H342N46O68 | KEGG DRUG (cross-referenced to PubChem)[6]; supplier data sheets[8] |
| Average molecular weight | ≈ 4,731.3 g/mol (Da) | KEGG 4,731.34[6]; Cayman 4,731.4[8] |
| Monoisotopic (exact) mass | ≈ 4,728.47 Da | KEGG DRUG[6] |
| Length | 39 amino acids, with non-standard residues (Aib, α-methyl-leucine) and a lipidated lysine | KEGG DRUG sequence[6]; supplier data[8] |
| CAS number | 2381089-83-2 | KEGG DRUG[6] |
What mass spectrometry actually shows
Big peptides don’t usually show up as a single peak at 4,731 in electrospray mass spec. They pick up several charges, so you see a series of peaks at the mass divided by the charge. For retatrutide, positive-mode peaks would land at roughly:
- [M+3H]3+ ≈ 1,578 m/z
- [M+4H]4+ ≈ 1,184 m/z
- [M+5H]5+ ≈ 947 m/z
These are our approximate calculations from the average molecular weight. Exact values depend on the instrument, mode (positive or negative) and whether average or monoisotopic mass is reported. A good certificate either lists the observed ions or reports the “deconvoluted” mass, meaning the peaks have been converted back to one molecular weight, which should match about 4,731. For an example of how this looks on a real certificate, a tirzepatide reference-standard COA from Cayman lists observed ions of 1,602.9 ([M−3H]3−) and 1,201.7 ([M−4H]4−) for a molecule of about 4,813.5 Da.[9]
Why the exact mass matters: lookalikes
The “GLP” drugs are close cousins, but their masses are distinct:
| Compound | Nickname | Molecular weight (approx.) |
|---|---|---|
| Semaglutide | “GLP-1”, “Sema” | 4,113.6 Da[7] |
| Retatrutide | “GLP-3”, “Reta”, “RT3” | 4,731.3 Da[6] |
| Tirzepatide | “GLP-2T”, “Tirz”, “TZ” | 4,813.5 Da[9] |
Retatrutide and tirzepatide differ by only about 82 Da, so a vague “GLP” label really could hide the wrong one. A properly reported mass spec result easily tells them apart. A purity number alone cannot.
Purity is not identity
This is the most common misunderstanding on certificates. HPLC tells you how much of the sample is one main compound (for example “99.2% purity”). It doesn’t tell you which compound that is. A vial of 99% pure tirzepatide labelled “GLP-3” would pass an HPLC purity check with flying colours. You need both:
- HPLC for purity (how clean)
- Mass spectrometry for identity (what it is)
Our step-by-step guide to how to read a peptide COA walks through every field, including how to tell whether the certificate matches your specific lot.
Red flags of mislabelled “GLP-3” products
Independent testing suggests quality problems in this market are common. Public Citizen’s report notes that the testing company Finnrick has tested 2,759 retatrutide samples since December 2024. Of 179 retatrutide vendors on its site, 71 (39.6%) were rated “poor”, “bad” or “fraud”, with many samples impure or off from their labelled amount.[10] Health Canada likewise warns that unauthorized peptides can contain incorrect amounts, unlisted ingredients or contaminants.[12]
Watch for these signs:
- The listing never names the molecule. A product called only “GLP-3”, with no mention of retatrutide or LY3437943 anywhere.
- No mass spec, or no molecular weight. A certificate that shows only an HPLC percentage hasn’t confirmed identity.
- The wrong mass. A reported molecular weight far from about 4,731 (for example near 4,813 or 4,114) means it isn’t retatrutide.
- A COA that isn’t tied to your lot. No batch or lot number, or a number that doesn’t match your vial. Watch for the same certificate image reused across products and years.
- No testing lab named, no test date, or a “lab” you can’t find.
- Brand-style names. Retatrutide has no brand name. Anything that pretends otherwise is marketing.
- Human-use claims. Before-and-after photos, “how much to take” charts or weight-loss promises signal a seller that isn’t operating as a research supplier.
- Prices that seem too good. Large peptides with non-standard residues are expensive to make well.
- Packaging tells. Off-colour labels, wrong date formats and faded text have been described in counterfeit GLP products.[10]
We cover more of these in How to spot fake peptides and Canadian vs imported peptides.
Retatrutide’s legal status in Canada
Whatever it’s called, retatrutide is not an approved medicine in Canada or anywhere else as of October 2026. Lilly states it is “legally available only to participants in Lilly’s clinical trials.”[13] Health Canada’s April 9, 2026 public advisory names retatrutide among unauthorized peptides that Canadians should not buy or use.[12] In phase 3, TRIUMPH-1 tested 4, 9 and 12 mg once weekly and reported average weight loss of up to 28.3% at 80 weeks.[13] Those are trial results under medical supervision, not a reason to self-experiment. For the regulatory timeline, see Is retatrutide approved? and Retatrutide in Canada.
If you’re a patient interested in this class of medicine, talk to your doctor or pharmacist. Approved options such as semaglutide (now available as a generic in Canada) and tirzepatide are prescribed and dispensed through pharmacies.
GLP-3 myths
“Myth: GLP-3 is a newly discovered hormone.”
No such hormone exists. Proglucagon gives rise to glucagon, GLP-1, GLP-2, glicentin and oxyntomodulin. There’s no GLP-3.[4] “GLP-3” is a nickname for retatrutide.
“Myth: GLP-3 means it’s three times stronger than a GLP-1.”
The 3 refers (loosely) to three receptors, not three times the potency. Retatrutide’s greatest in vitro potency is actually at the GIP receptor, not at GLP-1.[1][8]
“Myth: GLP-2 is the tirzepatide one.”
GLP-2 is a real gut hormone, and its drug analogue teduglutide (Revestive) treats short bowel syndrome.[5] Using “GLP-2” for tirzepatide is a vendor nickname that causes genuine confusion.
“Myth: If the label says RT3 or GLP-3, it’s retatrutide.”
A label is a claim. Only a batch-matched mass spec result showing a mass of about 4,731 Da backs it up.
“Myth: A 99% purity COA proves it’s the right peptide.”
Purity (HPLC) and identity (mass spec) are different tests. A pure sample of the wrong peptide is still the wrong peptide.
For researchers
TrueLabs lists retatrutide plainly as RT3 (Retatrutide), code LY3437943, from $90, for in vitro and laboratory research only. Each lot is tested for purity by HPLC and identity by mass spectrometry. We also supply TZ-2 (Tirzepatide) from $73 and Cagrilintide from $40. Before you use any lot, check its certificate against the numbers above. See How to read a peptide COA and browse the COA library.
FAQ
Tap a question to reveal the answer.
What is GLP-3?
“GLP-3” is an informal nickname for retatrutide, an experimental Eli Lilly drug that activates the GLP-1, GIP and glucagon receptors. It is not a natural hormone. The body makes GLP-1 and GLP-2 but no GLP-3.
Is GLP-3 the same as retatrutide?
When people say GLP-3, they almost always mean retatrutide (LY3437943). But because “GLP-3” isn’t an official name, a product labelled only “GLP-3” could contain anything. Only a batch-specific mass spec result can confirm it.
What is the RT3 peptide?
RT3 is a product code some suppliers, including TrueLabs, use for retatrutide. TrueLabs lists it as “RT3 (Retatrutide)” so the real compound name is always shown next to the code.
What does “Reta” mean?
“Reta” is common shorthand for retatrutide in forums and on social media. It refers to the same molecule as RT3, R3, GLP-3 and LY3437943.
Why don’t sellers just call it retatrutide?
Partly to get around social-media and advertising filters that block the drug’s real name, according to a 2026 Public Citizen report. Lilly’s legal pressure on sellers in 2026 added to that incentive. Some codes are ordinary catalogue SKUs, as long as the real name is disclosed.
What is the molecular weight of retatrutide?
About 4,731.3 g/mol, with the molecular formula C221H342N46O68 and a monoisotopic mass of about 4,728.5 Da, per KEGG DRUG. A mass spec result should match this.
How can I tell retatrutide from tirzepatide on a COA?
By mass. Retatrutide is about 4,731 Da and tirzepatide about 4,813 Da, a gap mass spectrometry resolves easily. An HPLC purity percentage alone can’t tell them apart.
Is GLP-2 a weight-loss drug?
No. Real GLP-2 is a gut hormone that maintains the intestinal lining, and its drug analogue teduglutide (Revestive) is approved in Canada for short bowel syndrome. Some sellers misuse “GLP-2” as a nickname for tirzepatide.
Is GLP-3 legal in Canada?
Retatrutide, by any name, is not an approved drug in Canada. Health Canada’s April 2026 advisory names it among unauthorized peptides and says “research use only” labels don’t exempt products from regulation. Patients should talk to a doctor about approved options.
Related reading
- What is retatrutide?
- Retatrutide vs Ozempic
- How to read a peptide COA
- How to spot fake peptides
- Is retatrutide approved?
- Retatrutide side effects
References
- Coskun T, Urva S, Roell WC, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234-1247. PubMed
- Urva S, Coskun T, Loh MT, et al. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet. 2022;400(10366):1869-1881. PubMed
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. N Engl J Med. 2023;389:514-526. PubMed
- Holst JJ. Glucagon and other proglucagon-derived peptides in the pathogenesis of obesity. Front Nutr. 2022;9:964406. DOI
- Health Canada. Summary Basis of Decision: Revestive (teduglutide). Drug and Health Product Portal. Health Canada
- KEGG DRUG. Retatrutide (D12430): formula, exact mass, molecular weight, CAS and PubChem cross-reference. KEGG
- KEGG DRUG. Semaglutide (D10025). KEGG
- Cayman Chemical. Retatrutide (Item 45527) product information: formula, formula weight and receptor EC50 values. Cayman Chemical
- Cayman Chemical. Certificate of Analysis, Tirzepatide (sodium salt), Item 39748, Batch 0824169 (mass spectrometry identity and HPLC purity). Cayman Chemical
- Whoriskey P. The “miracle drug” and the peptide craze: the HHS chief touts peptides as the agency looks the other way on retatrutide. Public Citizen, June 16, 2026. Public Citizen
- Outlook Business. Eli Lilly sues 6 US sellers over black-market retatrutide, calls products “unverified”. August 12, 2026. Outlook Business
- Health Canada. Think twice before injecting peptides bought online: unauthorized products can seriously harm your health. Public advisory, April 9, 2026. Health Canada
- Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1 topline). Press release, May 21, 2026. Lilly
This article summarizes published research and regulatory information for information only and is not medical advice. TrueLabs research compounds are sold for in vitro and laboratory research use only and are not intended for human or veterinary use.