The short answer: GLP-3 does not exist
Type "GLP-3" into a search bar and most of what comes back is about retatrutide, an Eli Lilly obesity drug in late-stage trials. That is a naming shortcut, not biology. Glucagon-like peptide-1 (GLP-1) is a real gut hormone with a well-mapped receptor. There is no GLP-2 or GLP-3 hormone that retatrutide activates; GLP-2 is in fact a separate, real hormone involved in intestinal growth, unrelated to weight drugs. Retatrutide's actual mechanism is three receptors from two different hormone families, not one family extended by one more member.
Where the nickname comes from
The name follows a pattern people noticed across three generations of drugs:
- Semaglutide (Ozempic, Wegovy) activates one receptor: GLP-1.
- Tirzepatide (Mounjaro, Zepbound) activates two: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide).
- Retatrutide activates three: GLP-1, GIP, and glucagon.
Calling retatrutide "GLP-3" extends that counting pattern as if each drug simply added another member of the GLP-1 family. It has not. GIP and glucagon are structurally related to GLP-1 as members of the same broader hormone superfamily, but they are distinct hormones with their own receptors and their own separate roles in the body. The nickname is a piece of marketing shorthand born on social media and forums, not a name Eli Lilly, the FDA, or any published trial paper uses. Lilly's own designation for the drug is LY3437943, described in its papers as a triple GIP, GLP-1 and glucagon receptor agonist.
What the three real receptors do
GLP-1 receptor. The mechanism shared with semaglutide and tirzepatide: insulin release rises when glucose is high, glucagon (the hormone, not the receptor target discussed next) falls, the stomach empties more slowly, and appetite drops through receptors in the brain's feeding centres.
GIP receptor. The second target tirzepatide already uses. GIP is released from the gut after eating and also affects insulin secretion and fat tissue metabolism. Retatrutide's discovery paper describes it as having more GIP receptor activity relative to its GLP-1 and glucagon activity, in cell-based assays.
Glucagon receptor. This is retatrutide's distinguishing addition. Glucagon is best known for raising blood sugar, which sounds like the wrong direction for a diabetes or obesity drug, but it also drives energy expenditure and fat breakdown in the liver. In the discovery research, Lilly's team reported that in obese mice, the glucagon-driven rise in energy expenditure added to the drop in food intake coming from the GIP and GLP-1 activity, a combination not present in semaglutide or tirzepatide.
The pharmacology, in short, is two families and three targets, deliberately combined rather than a fourth member of the GLP-1 line.
What the trials have actually found
Every figure below comes from Lilly's peer-reviewed phase 2 paper or its own topline trial announcements. Each trial enrolled a different population over a different length of time, so the numbers describe separate studies, not one continuous result.
| Trial | Date | Participants | Duration | Mean weight loss |
|---|---|---|---|---|
| Phase 2 (Jastreboff, NEJM) | 2023 | 338 | 48 weeks | 24.2% (12 mg arm) |
| TRIUMPH-4 (knee osteoarthritis) | 11 Dec 2025 | 445 | 68 weeks | 28.7% |
| TRIUMPH-1 (obesity) | 21 May 2026 | 2,339 | 80 weeks | 28.3% (30.3% at 104 weeks) |
| TRIUMPH-2 (type 2 diabetes) | 23 Jul 2026 | 1,152 | 20.8%, A1C down 1.6 points | |
| TRIUMPH-3 (cardiovascular disease) | 23 Jul 2026 | 1,949 | 22.6% |
In TRIUMPH-1, the main phase 3 obesity trial, individual dose arms reported 19.0% mean weight loss on 4 mg and 25.9% on 9 mg, against 2.2% on placebo. TRIUMPH-4, in people with obesity and knee osteoarthritis, reported relief of knee pain alongside its weight loss figure. TRIUMPH-2 and TRIUMPH-3 tested people with type 2 diabetes and established cardiovascular disease respectively, populations where safety and metabolic questions carry more weight than in a general obesity trial.
None of the trials above has yet reported hard cardiovascular outcomes such as heart attacks or deaths; TRIUMPH-3 enrolled people with cardiovascular disease but reported a weight loss figure, not an event-rate result.
The one safety signal that stands out
TRIUMPH-4 reported dysesthesia, an abnormal skin sensation such as tingling, prickling or burning, in 20.9% of participants on the 12 mg dose, against 0.7% on placebo. This has not been reported at this frequency for semaglutide or tirzepatide, and what causes it, and whether it persists or resolves, has not been explained in the topline data available. The side effect management guide covers the gastrointestinal effects common to the whole GLP-1 class; dysesthesia is a separate, retatrutide-specific finding worth knowing by name if the drug becomes available.
Where retatrutide actually stands
As of September 2026, retatrutide is not approved anywhere. Lilly has said it plans to submit a Biologics License Application to the US FDA in the first quarter of 2027. It is not registered with FDA Philippines, and no pharmacy here can legally sell it as a medicine. Two other drugs that add a glucagon-receptor component are further along in some markets: mazdutide, already approved in China, and survodutide, also in trials. None of that regulatory picture changes because of a nickname; it changes when a completed Phase 3 programme reaches a regulator's desk.
Status in the Philippines
Retatrutide is not registered with FDA Philippines and has no approval from any regulator worldwide, so what circulates locally is sold as a research compound rather than a medicine. FDA Philippines and the NBI have acted against unregistered GLP-1 sales in 2026, including a tirzepatide case in Tondo in May and a raid on a Pasig clinic later that month. The "GLP-3" label attached to retatrutide online has no bearing on that regulatory status either way.
