Retatrutide is the next-generation triple agonist (GLP-1, GIP and glucagon) currently in late-stage Eli Lilly trials. Tirzepatide is the FDA-approved dual agonist already on-market as Mounjaro/Zepbound. Both circulate on the Australian research-peptide market - but retatrutide is not yet a registered medicine anywhere.
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptor targets | GLP-1 + GIP + glucagon (triple) | GLP-1 + GIP (dual) |
| Regulatory status | Phase 3 trials (LLY) | FDA / TGA approved |
| Molecular weight | ~4731 Da | ~4814 Da |
| Half-life | ~6 days | ~5 days |
| Phase 2 mean weight loss (48 wk) | ~24% | ~21% (SURMOUNT-1, 72 wk) |
| Typical research dose | 2 → 12 mg weekly | 2.5 → 15 mg weekly |
| AU grey-market availability | High (no licensed equivalent) | High |
| Identity (LC-MS) expected mass | 4731 Da | 4814 Da |
| Counterfeit/substitution risk | Very high - often sold as a cheap GLP-1 instead | Medium |
Retatrutide's Phase 2 data is the best in the GLP-1 class, but no regulator has approved it - every vial in Australia is research-grade. Because there is no licensed reference, vendor risk is highest here. Tirzepatide is the safer-on-paper choice; retatrutide is the higher-upside option. Both warrant LC-MS identity before use.