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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 Phase 3 obesity trial results are expected in late 2026. The weight loss figures above are from Phase 2 (obesity) and Phase 3 (type 2 diabetes) trials. 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: Retatrutide looks like it will be the more powerful compound when its obesity Phase 3 data arrives. But Tirzepatide is available now, has an excellent track record, and is the right choice for the vast majority of people today. Think of Tirzepatide as the current gold standard and Retatrutide as the next evolution — not yet available, but worth watching closely.
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.