GLP-3 Explained: Why Retatrutide Gets Called GLP-3

What GLP-3 actually is

GLP-3 is a nickname, not a hormone. There is no GLP-3 receptor in the body,¹ and there is no molecule called glucagon-like peptide 3.³ The human pro-glucagon gene, the source of the glucagon-like peptides, produces a fixed set of eight peptides, and the numbered glucagon-like peptides stop at two: GLP-1 and GLP-2. Neither the string GLP-3 nor glucagon-like peptide 3 appears anywhere in the reference protein record for human pro-glucagon.³

So where did the name come from. It is informal, it started online, and it travels with promotional claims that these drugs outperform older weight-loss medicines and even promote longevity, claims the sources trace mostly to early research.² It is used in two ways: as shorthand for one drug, retatrutide, and as a loose class label for the new triple-hormone-receptor agonists in general.¹ Either way, the term describes a marketing category, not a hormone a biologist would recognize.

Where the number 3 comes from

The 3 is a receptor count, not a hormone name. The first generation of these drugs hit one target: GLP-1 drugs such as semaglutide act on a single pathway, the glucagon-like peptide-1 receptor, to slow gastric emptying, lower blood sugar, and reduce appetite.¹ The next generation added a second target. Tirzepatide, sold as Zepbound and Mounjaro, is a dual agonist that acts on GLP-1 and GIP.¹ Retatrutide adds a third pathway, the glucagon receptor, and that is why it is sometimes called a GLP-3 or a triple agonist.²

Sources for the table above: [1][2].

As one consumer explainer lays out the three targets, each does a different job in metabolism:

Here is the catch the name hides: only one of those three targets is actually a glucagon-like peptide. GIP is a separate hormone, glucose-dependent insulinotropic polypeptide, and glucagon is the parent hormone that pro-glucagon is named for.³ GLP-1 is the only glucagon-like peptide in the mix.¹ Counting up to GLP-3 treats three different hormone systems as if they were three rungs on one ladder, and they are not.

The three activities are not even equal in strength. In the laboratory, the discovery paper reported that the molecule shows balanced activity at the glucagon and GLP-1 receptors but more activity at the GIP receptor.⁵ So even inside the single molecule, the three pathways are weighted differently, which is another reason a tidy 1, 2, 3 count misreads the biology.

The real GLP-2, and the ladder that never existed

If you assume GLP-1 was followed by GLP-2 and then GLP-3, the numbering falls apart at the second step. GLP-2 is real, but it has nothing to do with weight loss. It is a gut hormone: it stimulates intestinal growth and the height of the villi that line the small intestine, and the tract from stomach to colon is its principal target.³ It already has an approved drug, and that drug is not for obesity. Teduglutide, sold as GATTEX, is a 33 amino acid GLP-2 analog approved for short bowel syndrome in adults and children who depend on parenteral support.⁴

So the real second rung of the GLP ladder is a gut drug, not a fat-loss drug, and there is no third rung at all. This is what breaks the intuitive GLP-1, GLP-2, GLP-3 sequence. Retatrutide is not GLP-3 in any literal sense. It is a triple agonist that happens to include one glucagon-like peptide receptor among its three targets, alongside two receptors that are not glucagon-like peptides.

Sources for the table above: [1][2][3][4].

Retatrutide, the drug behind the nickname

The drug the GLP-3 label most often points to is retatrutide, development code LY3437943, from Eli Lilly.⁶ It is a single peptide, one synthetic molecule, not a combination of three separate drugs.⁵⁹ It is investigational: as of August 2026 it is not approved by the FDA and is not available to the public,² the phase 3 program describes it as under clinical development,⁸ and none of the sources reviewed for this page record an approval in any market. This page does not restate the full trial record. The dose-by-dose data lives on the retatrutide profile. What matters for the naming question is simply that the evidence base is real and large.

To put one figure on that: in the phase 2 obesity trial, adults received once-weekly subcutaneous retatrutide at maintenance doses of 1 mg to 12 mg, or placebo (trial doses, not a recommendation, PMID 37366315), and at 48 weeks the least-squares mean body weight fell by 24.2% at the 12 mg dose, versus 2.1% with placebo (phase 2 trial, PMID 37366315).⁶ Beyond that single trial, a dedicated phase 3 obesity program called TRIUMPH spans four studies and more than 5,800 participants.⁹ The dose-by-dose figures for those, and for the separate diabetes and liver-fat trials, belong on the profile, not on an explainer about the name.

The mechanism behind that third pathway showed up first in animals. In obese mice, the molecule lowered body weight and improved glucose control, and the glucagon pathway added increases in energy expenditure on top of the appetite reduction driven by the GIP and GLP-1 receptors.⁵ That is the point of the third receptor, and it is why the nickname attaches to a triple agonist rather than to any older single or dual drug. A result like this describes a mechanism in mice, not a human outcome, and does not carry over to people on its own.

Side effects and the missing label

Because retatrutide has no approved label, there is no official side-effect list, only what clinical trials have reported so far. In broad terms those trials describe mostly mild to moderate gastrointestinal effects, such as nausea, that are dose related and were partly reduced by starting at a lower dose.⁶⁷ The trial-by-trial adverse-event rates sit on the retatrutide profile; this page keeps to the two points that matter for anyone who has met the drug only as a nickname.

The first is an open question, not a settled fact. GLP-1 drugs carry a boxed warning about a risk of thyroid cancer, and it is not yet known whether the triple agonists will carry a similar risk.¹ Retatrutide has no approved label, so it has no boxed warning of its own either way, and this page will not guess which way that lands.

The second is practical. Retatrutide is not sold as an approved medicine in any of these sources, so anything marketed as GLP-3 or retatrutide for sale online sits outside a regulated supply chain, where identity, purity and dose cannot be verified. Both consumer sources reviewed here say the same thing: do not buy unverified peptides or GLP-3s online.¹² This page does not point anyone to a source.

GLP-3 and retatrutide in Vietnam

For readers in Vietnam, the short version is that retatrutide is not carried by Long Chau, the country's largest retail pharmacy chain. On 2026-09-06, a search for retatrutide there returned no products at all.¹⁰ That is a genuine result, not a failed page load: the same search for an injectable GLP-1 drug, Saxenda, returned hundreds of listings on the same day, so the chain does serve these results to a plain fetch and simply does not carry retatrutide.¹⁰

Absence from one pharmacy chain is not the same as absence from the national drug register, and the register operated by the Drug Administration of Vietnam could not be searched for retatrutide within the sources gathered here. The clearest published statement of the drug's Vietnamese status comes from the Ministry of Health's own newspaper, Suc khoe and Doi song, which says retatrutide is not currently approved for use in clinical practice.¹¹ No price is quoted, because none was shown on the listing that was checked. The compound does have a Vietnamese nickname in circulation: the same article calls it thuoc ba G, the three G drug, the local equivalent of the GLP-3 shorthand.¹¹

The short version

Sources & references

1. 1.Healthline. What Are GLP-3s? A dedicated consumer explainer stating there is no GLP-3 receptor, that GLP-3 medications target three metabolic pathways, and that these drugs are not FDA approved or available. Reviewed by Alex Nguyen, PharmD; written by Kaylea Swearingen, PharmD, July 27, 2026. healthline.com/health/drugs/what-are-glp-3s
2. 2.Healthline. Retatrutide vs. Tirzepatide: Facts About the Trend. States that retatrutide adds a third pathway, the glucagon receptor, that this is why it is called a GLP-3 or triple agonist, and that as of August 2026 it is not FDA approved and not available to the public. Reviewed by Kiran Khanani, PharmD; written by Sandra Silva, August 11, 2026. healthline.com/health/drugs/retatrutide-vs-tirzepatide
3. 3.UniProtKB P01275 (GLUC_HUMAN), human pro-glucagon, reviewed Swiss-Prot record. Lists the eight peptides cleaved from the 180 amino acid precursor, ending at glucagon-like peptide 2; no GLP-3 or glucagon-like peptide 3 appears. Retrieved 2026-09-06. uniprot.org/uniprotkb/P01275
4. 4.DailyMed. GATTEX (teduglutide) prescribing information, Takeda Pharmaceuticals America, Inc. A glucagon-like peptide-2 (GLP-2) analog indicated for adults and pediatric patients with short bowel syndrome dependent on parenteral support. SPL version 20, published September 18, 2025; retrieved 2026-09-06. dailymed.nlm.nih.gov / GATTEX teduglutide
5. 5.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 Metabolism, 2022. Reports the three receptors, balanced GCGR and GLP-1R activity with more GIPR activity in vitro, obese mouse results, and a phase 1 single ascending dose study. PMID 35985340. pubmed.ncbi.nlm.nih.gov/35985340
6. 6.Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine, 2023. Once-weekly subcutaneous retatrutide versus placebo across escalating dose arms, n = 338, 48 weeks; dose-dependent body weight reductions, largest in the highest-dose group. Registered NCT04881760. PMID 37366315. pubmed.ncbi.nlm.nih.gov/37366315
7. 7.Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. Lancet, 2023. Reports gastrointestinal adverse events in about 35% of the retatrutide group, no severe hypoglycaemia and no deaths, and a safety profile consistent with GLP-1 receptor agonists. PMID 37385280. pubmed.ncbi.nlm.nih.gov/37385280
8. 8.Efficacy and safety of retatrutide, a GIP, GLP-1 and glucagon receptor agonist, in people with type 2 diabetes (TRANSCEND-T2D-1): a completed phase 3 trial of once-weekly subcutaneous retatrutide versus placebo, n = 537. Lancet, 2026. Registered NCT06354660. PMID 42250575. pubmed.ncbi.nlm.nih.gov/42250575
9. 9.Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism, 2026. Four phase 3 studies of weekly subcutaneous retatrutide versus placebo in over 5,800 participants. PMID 41090431. pubmed.ncbi.nlm.nih.gov/41090431
10. 10.Nha Thuoc Long Chau, retail pharmacy search for retatrutide, retrieved 2026-09-06. Returned zero products; a same-day control search for Saxenda returned results, confirming the null is genuine for this chain rather than a fetch failure. No price shown. nhathuoclongchau.com.vn / retatrutide search
11. 11.Bao Suc khoe and Doi song, the newspaper of the Vietnamese Ministry of Health. States "Hien tai, retatrutide chua duoc phe duyet de su dung trong thuc hanh lam sang" (retatrutide is not currently approved for use in clinical practice), and calls the drug "thuoc ba G" (the three G drug). Retrieved 2026-09-06. suckhoedoisong.vn / Ministry of Health newspaper