Short answer: Tirzepatide activates two receptors (GIP + GLP-1). Retatrutide activates three (GIP + GLP-1 + glucagon). Phase II retatrutide data showed larger body composition changes than tirzepatide Phase III, but retatrutide lacks FDA approval and Phase III data as of 2026.
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| Criteria | Tirzepatide | Retatrutide |
|---|---|---|
| Receptors | GLP-1 + GIP | GLP-1 + GIP + Glucagon |
| Max weight reduction (published) | 22.5% (72wk Phase III) | ~24% (48wk Phase II) |
| Glucagon pathway | No | Yes — hepatic lipid oxidation |
| FDA approval status | Approved (2 indications) | Phase III trials |
| Published research base | Extensive | Growing rapidly |
| Best for | Established dual-receptor studies | Triple-agonist / glucagon pathway research |
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Tirzepatide is a dual GIP/GLP-1 receptor agonist. Retatrutide is a triple agonist targeting GIP, GLP-1, and glucagon receptors simultaneously. The addition of glucagon receptor agonism in retatrutide enables hepatic lipid oxidation and energy expenditure pathways not activated by tirzepatide.