Both are from Eli Lilly. Both target GLP-1 and GIP. But one adds a third receptor that changes everything. Here is the full breakdown.
Both compounds are from Eli Lilly and share the same GLP-1 and GIP foundation. The critical difference is that Retatrutide adds a third receptor — glucagon — which is responsible for its superior metabolic effects.
| Feature | Retatrutide | Tirzepatide |
|---|---|---|
| GLP-1 Receptor | ||
| GIP Receptor | ||
| Glucagon Receptor | ||
| Metabolic Rate Boost | ||
| FDA Approved | ||
| Liver Fat Reduction | ||
| Long-term Safety Data |
Direct head-to-head trials between Retatrutide and Tirzepatide have not been completed. The comparison below draws on the best available data from each compound's own Phase 2 and Phase 3 trials.
* Retatrutide TRIUMPH-4 Phase 3 obesity trial results were announced December 2025 (28.7% weight loss, avg 71.2 lbs). Tirzepatide figures are from SURMOUNT-1 and SURPASS trials.
Both compounds are once-weekly subcutaneous injections with a slow titration schedule to minimize GI side effects. The key practical difference is that Tirzepatide is available as a pre-filled pen device, while Retatrutide is currently only available as a research vial requiring reconstitution.
| Aspect | Retatrutide | Tirzepatide |
|---|---|---|
| Starting Dose | 1–2.5 mg/week | 2.5 mg/week |
| Maintenance Dose | 4–12 mg/week | 5–15 mg/week |
| Frequency | Once weekly | Once weekly |
| Route | Subcutaneous injection | Subcutaneous injection |
| Titration Schedule | Every 4–6 weeks | Every 4 weeks |
| Pen Device Available | No (research vial only) | Yes (KwikPen) |
| Typical Cycle | 12–48 weeks | Ongoing (chronic) |
The side effect profiles of both compounds are very similar, which makes sense given their shared GLP-1 and GIP mechanisms. GI effects are the most common and are largely managed through slow dose titration.
| Side Effect | Retatrutide | Tirzepatide |
|---|---|---|
| Nausea | Common (titration phase) | Common (titration phase) |
| Vomiting | Occasional | Occasional |
| Diarrhea | Occasional | Occasional |
| Constipation | Mild | Common |
| Decreased Appetite | Yes (intended) | Yes (intended) |
| Injection Site Reactions | Mild | Mild |
| Hypoglycemia (without insulin) | Low risk | Low risk |
| Pancreatitis (rare) | Theoretical | Rare (reported) |
The honest answer: The TRIUMPH-4 Phase 3 data (Dec 2025) confirmed Retatrutide is the more powerful compound — 28.7% weight loss vs. 22.5% for tirzepatide. But Tirzepatide is FDA approved, available by prescription today, and has an excellent real-world safety record. Think of Tirzepatide as the current gold standard and Retatrutide as the next evolution — extraordinary data, but not yet available outside of clinical trials.
Educational Disclaimer: This comparison is for informational purposes only and does not constitute medical advice. Retatrutide is not FDA approved and is available for research use only. Tirzepatide requires a prescription from a licensed healthcare provider. Clinical data cited is from published Phase 2 and Phase 3 trials; individual results vary. Always consult a qualified healthcare provider before starting any medication or peptide protocol.