| Dimension | Retatrutide | Tirzepatide |
|---|---|---|
| Class | GLP-1 / GIP / glucagon agonist | GLP-1 / GIP agonist |
| Category | GLP-1 | GLP-1 |
| Common vial sizes | 5 / 10 mg | 5 / 10 / 15 mg |
| Typical dose range | 1 mg – 12 mg | 2.5 mg – 15 mg |
| Half-life | ~6 days | ~5 days |
| Status | Research compound | FDA-approved formulation exists |
Educational reference only. Not medical advice — follow the instructions from your clinician or pharmacy.
Triple vs dual agonist
Retatrutide targets three receptors (GLP-1, GIP, and glucagon); tirzepatide targets two (GLP-1 and GIP). The extra glucagon activity is the headline difference and is why retatrutide is studied at its own dose range rather than tirzepatide's.
For reconstitution, both are handled the same way — only the milligram numbers and vial sizes differ, as the table above shows.
- Retatrutide: GLP-1 + GIP + glucagon (triple)
- Tirzepatide: GLP-1 + GIP (dual)
- Separate dose ranges — not interchangeable
Maturity and how it affects sourcing
Tirzepatide has an approved formulation; retatrutide is still investigational. That difference does not change the calculator math, but it does mean retatrutide doses come from research vials rather than an approved product, so confirm your vial strength carefully before calculating.
Whichever you use, run your real vial and water numbers through the relevant calculator to get the exact draw.