What it is
Retatrutide (LY3437943) is an investigational Eli Lilly peptide that activates three hormone receptors at once: GIP, GLP-1 and glucagon. It follows semaglutide, which hits one of those receptors, and tirzepatide, which hits two.
It is not an approved medicine anywhere. Everything known about it in people comes from Lilly's clinical trial programme. The online nickname "GLP-3" is shorthand for the three targets, not a real hormone. The GLP-3 retatrutide explainer covers the naming and the hype in more depth.
How it works
The GIP and GLP-1 arms work the way they do in tirzepatide: more glucose-dependent insulin, slower stomach emptying and less appetite.
The glucagon arm is the new part. Glucagon normally raises blood sugar, which sounds like the wrong direction for a diabetes drug, but it also increases energy expenditure and fat burning in the liver. In the discovery paper, Lilly's team reported that in obese mice the glucagon-driven rise in energy expenditure added to the drop in food intake from GIP and GLP-1. In cell assays, retatrutide showed balanced glucagon and GLP-1 receptor activity with more GIP receptor activity.
In the phase 1b study in people with type 2 diabetes, the half-life was about six days, which supports weekly injection.
What the research found
All of the data below is human. Figures come from peer-reviewed papers (phase 2) or Eli Lilly's topline announcements (phase 3). Each trial enrolled a different population, so the numbers should not be mixed or compared as if they came from one study.
| Trial | Date | People | Length | Mean weight loss |
|---|---|---|---|---|
| Phase 2 (NEJM) | 2023 | 338 | 48 weeks | 24.2% at 12 mg |
| TRIUMPH-4 | 11 Dec 2025 | 445, with knee osteoarthritis | 68 weeks | 28.7% |
| TRIUMPH-1 | 21 May 2026 | 2,339 | 80 weeks | 28.3% (30.3% at 104 weeks) |
| TRIUMPH-2 | 23 Jul 2026 | 1,152, with type 2 diabetes | 20.8%, A1C down 1.6 points | |
| TRIUMPH-3 | 23 Jul 2026 | 1,949, with cardiovascular disease | 22.6% |
Phase 2. Adults with obesity, or overweight with a weight-related condition, were randomised to one of several weekly doses or placebo for 48 weeks. Weight loss was dose-related, with the 12 mg arm reaching 24.2%.
TRIUMPH-1. The main phase 3 obesity trial. Lilly reported mean weight loss of 19.0% on 4 mg and 25.9% on 9 mg, against 2.2% on placebo, with the top-line figure of 28.3% at 80 weeks and 30.3% at 104 weeks.
TRIUMPH-4. Tested retatrutide in people with obesity and knee osteoarthritis, and reported relief of knee pain alongside 28.7% mean weight loss.
TRIUMPH-2 and TRIUMPH-3. In people with type 2 diabetes, Lilly reported 20.8% mean weight loss and an A1C fall of 1.6 points. TRIUMPH-3, in people with established cardiovascular disease, reported 22.6%.
None of these trials has yet reported hard outcomes such as heart attacks, strokes or deaths.
Side effects reported in studies
In phase 2, the most common adverse events were gastrointestinal. They were dose-related and mostly mild to moderate in severity.
TRIUMPH-4 flagged something newer: dysesthesia, an abnormal skin sensation such as tingling or burning, was reported in 20.9% of people on 12 mg vs 0.7% on placebo. What causes it and whether it persists is not yet clear from topline data. The full phase 3 papers and FDA review will give a complete safety picture; until then, unlisted risks cannot be ruled out. The side effect management guide covers the GI effects common to the class.
Retatrutide vs tirzepatide
| Tirzepatide | Retatrutide | |
|---|---|---|
| Receptors | GIP, GLP-1 | GIP, GLP-1, glucagon |
| Half-life | About 5 days | About 6 days |
| Status | Approved (Mounjaro, Zepbound) | Investigational, FDA filing planned Q1 2027 |
| Sold in PH pharmacies | Mounjaro | No |
Two other glucagon-containing compounds are further along or in parallel: mazdutide, already approved in China, and survodutide.
Status in the Philippines
Retatrutide is not approved by any regulator and is not registered with FDA Philippines, so no pharmacy or clinic can legally sell it as a medicine. What circulates locally is sold as a research compound. The NBI and FDA Philippines have acted against unregistered GLP-1 sales in 2026, including tirzepatide sellers in Tondo in May and a Pasig clinic later that month. Lilly plans its US FDA submission in the first quarter of 2027.
Local stock Retatrutide at Primara Labs, delivered in Metro Manila and nationwide. Research use only.
Storage
Research vials are supplied as a lyophilised powder. Keep them refrigerated, and once mixed with bacteriostatic water, hold them at 2 to 8°C away from the freezer compartment. Heat is the main risk in the Philippines: a brownout or a day in a hot car can push a vial well above safe range. The retatrutide reconstitution calculator handles the mixing arithmetic.
