Last updated: May 18, 2026
What retatrutide is
Retatrutide is a synthetic 39-amino-acid peptide developed by Eli Lilly that activates three incretin/glucagon family receptors with a single molecule: GLP-1, GIP, and glucagon. The triple-agonist design produces additive metabolic effects beyond what dual-agonist tirzepatide achieves.
Mechanism
The molecule combines three signaling pathways:
- GLP-1 receptor: enhances glucose-dependent insulin secretion, suppresses glucagon, delays gastric emptying, reduces appetite
- GIP receptor: additional insulin secretion, central appetite reduction via distinct pathways from GLP-1
- Glucagon receptor: increases energy expenditure, hepatic lipid oxidation, and basal metabolic rate
The glucagon component is the differentiator vs tirzepatide. Increasing energy expenditure while reducing appetite produces a “two-sided” weight loss effect.
Phase 2 efficacy
TRIUMPH-1 Phase 2 (NEJM 2023, 338 adults with obesity, 48 weeks):
- 1 mg/week: -8.7% mean weight loss
- 4 mg/week: -17.1%
- 8 mg/week: -22.8%
- 12 mg/week: -24.2%
- Placebo: -2.1%
The 12mg dose produced ~5 percentage points more weight loss than the highest dose of tirzepatide in equivalent populations — a meaningful additional effect.
Side effect profile
Similar overall to GLP-1/GIP agonists: nausea, vomiting, diarrhea, constipation during titration. The glucagon component adds modest heart rate increase (~5 bpm) and mild elevation in fasting glucose (offset by the GLP-1 component overall).
Development timeline
Phase 3 TRIUMPH program ongoing across obesity, type 2 diabetes, MASH (liver disease), and obstructive sleep apnea. Initial Phase 3 readout for obesity expected 2026. FDA submission likely late 2026 or early 2027.
Retatrutide vs semaglutide vs tirzepatide
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Mechanism | GLP-1 | GLP-1 + GIP | GLP-1 + GIP + Glucagon |
| Phase 3 weight loss | ~15% | ~21% | ~24% (Phase 2) |
| Status | Approved | Approved | Phase 3 |
When will retatrutide be available?<br />
Phase 3 results expected 2026, FDA submission late 2026 / early 2027. Approval probable for late 2027 or 2028. Not currently available outside clinical trials.
How does retatrutide compare to tirzepatide?<br />
Triple-agonist mechanism (adds glucagon receptor) produced ~3-5 percentage points more weight loss in equivalent trials. The glucagon component increases energy expenditure in addition to appetite reduction.
Are there compounded versions of retatrutide?<br />
No legitimate compounded versions exist — retatrutide is not yet FDA-approved and is not on an FDA shortage list. Any sellers claiming “compounded retatrutide” should be regarded with extreme skepticism.
Is retatrutide safer than other GLP-1 drugs?<br />
Phase 2 safety profile is broadly similar to GLP-1/GIP class. Phase 3 data with longer exposure is needed to characterize the full safety profile.