Retatrutide is the next-generation weight-loss drug generating excitement, and it has now produced head-turning Phase 3 results compared with tirzepatide. Here is how the two compare and where retatrutide stands.
Quick answer
Retatrutide is an investigational "triple agonist" from Eli Lilly that targets three receptors (GLP-1, GIP, and glucagon), versus tirzepatide's two (GLP-1 and GIP). In Phase 3 TRIUMPH-1 results reported in 2026, retatrutide produced roughly 28% to 30% average weight loss at higher doses, exceeding tirzepatide's SURMOUNT-1 result of up to about 22.5%. Retatrutide is not yet FDA-approved, while tirzepatide (Mounjaro, Zepbound) is. If approved, retatrutide could become the most powerful weight-loss drug to date, but it is still in trials.
What is retatrutide?
Retatrutide is an investigational once-weekly injectable from Eli Lilly. What sets it apart is that it acts on three receptors at once: GLP-1, GIP, and glucagon. Tirzepatide hits two (GLP-1 and GIP), and semaglutide hits one (GLP-1). Adding the glucagon receptor is thought to boost energy expenditure on top of appetite suppression, which may explain its strong weight-loss results.
It is sometimes described as a potential successor to tirzepatide, though it is still in clinical trials and not yet approved.
Retatrutide vs tirzepatide: the head-to-head picture
There is no single randomized head-to-head trial between the two, but their Phase 3 results can be compared.
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Try the BMI Calculator →- Tirzepatide (SURMOUNT-1): Up to about 22.5% average weight loss at 72 weeks (15 mg) in adults with obesity.
- Retatrutide (TRIUMPH-1, reported 2026): Roughly 28% to 30% average weight loss at higher doses, the highest reported for a pharmacological obesity treatment in a large Phase 3 trial.
On the numbers, retatrutide's reported results exceed tirzepatide's. That is a notable margin, and it is why retatrutide has generated so much attention. The caveat is that cross-trial comparisons are not as definitive as a direct head-to-head study.
Comparison table
| Feature | Tirzepatide | Retatrutide |
|---|---|---|
| Receptors targeted | GLP-1 + GIP (dual) | GLP-1 + GIP + glucagon (triple) |
| Phase 3 weight loss | Up to ~22.5% (SURMOUNT-1) | ~28% to 30% (TRIUMPH-1, reported) |
| Status | FDA-approved (Mounjaro, Zepbound) | Investigational, in Phase 3 |
| Dosing | Once weekly | Once weekly |
Why the extra receptor may matter
Tirzepatide's success showed that hitting two gut-hormone systems beat hitting one. Retatrutide extends that logic by adding glucagon-receptor activity, which can increase the body's energy expenditure. Combining appetite suppression (from GLP-1 and GIP) with increased energy use (from glucagon) is the theory behind its larger weight loss. The strong TRIUMPH results lend support to that idea, though long-term data and the full safety picture are still being established.
What about side effects?
As with other drugs in this class, the side-effect profile is dominated by gastrointestinal effects (nausea, vomiting, diarrhea), which tend to be dose-related and managed with gradual titration. Because retatrutide is still investigational, its complete safety profile is being characterized through ongoing trials. Comparing tolerability definitively will require more data.
When might retatrutide be available?
Retatrutide is in Phase 3 trials, with multiple TRIUMPH studies reading out through 2026. It is not yet FDA-approved, and approval and availability depend on completing the trial program and regulatory review. For now, tirzepatide and semaglutide are the approved options; retatrutide is one to watch.
Where FormBlends fits
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Frequently asked questions
Is retatrutide better than tirzepatide? In reported Phase 3 results, retatrutide produced more average weight loss (about 28% to 30%) than tirzepatide (up to about 22.5%). But retatrutide is investigational and not yet approved.
How does retatrutide work? It is a triple agonist targeting GLP-1, GIP, and glucagon receptors, combining appetite suppression with increased energy expenditure.
Is retatrutide FDA-approved? No. It is in Phase 3 trials. Tirzepatide (Mounjaro, Zepbound) is the approved option.
How much weight loss did retatrutide show? Reported TRIUMPH-1 results showed roughly 28% to 30% average weight loss at higher doses.
What is the difference between retatrutide and tirzepatide? Retatrutide targets three receptors (adding glucagon); tirzepatide targets two. Retatrutide showed greater reported weight loss but is not yet approved.
When will retatrutide be available? It is still in Phase 3 trials reading out through 2026. Availability depends on completing trials and regulatory review.
Are the side effects different? Both are dominated by gastrointestinal effects. Retatrutide's full safety profile is still being established in trials.
Is retatrutide a successor to tirzepatide? It is often described that way given its stronger reported results, but it must complete trials and gain approval first.
Sources
- AJMC, retatrutide TRIUMPH-1 Phase 3 results: https://www.ajmc.com/view/retatrutide-achieves-up-to-30-3-average-weight-loss-in-phase-3-triumph-1-trial
- New England Journal of Medicine, SURMOUNT-1 tirzepatide obesity trial: https://www.nejm.org/doi/full/10.1056/NEJMoa2206038