Quick verdict
Tirzepatide is the practical choice today: it is a dual GIP/GLP-1 agonist that is FDA-approved (Mounjaro for type 2 diabetes, Zepbound for obesity) and available by prescription now. Retatrutide is a triple GLP-1/GIP/glucagon agonist that produced higher weight loss in its Phase 2 trials (~24% at 48 weeks vs tirzepatide's ~22.5% at 72 weeks), but it remains investigational — no FDA approval, no legal commercial supply, and no head-to-head or cardiovascular-outcomes data. If you need treatment now, tirzepatide is the only real option; retatrutide is the compound to watch as Phase 3 reads out.
| Attribute | Retatrutide | Tirzepatide |
|---|---|---|
| Class | Triple Incretin Agonist | GIP/GLP-1 Receptor Agonist |
| FDA Status | Research Use | FDA Approved |
| Primary Uses | Weight Loss, Type 2 Diabetes, Metabolic Health | Weight Loss, Type 2 Diabetes |
| Administration | Subcutaneous injection | Subcutaneous Injection |
| Typical Dosing | Investigational — no FDA-approved dose. Phase 2 obesity trials used 2, 4, 8, and 12 mg once-weekly subcutaneous injections, titrated gradually over roughly 24 weeks, with 12 mg producing the greatest weight loss. These figures are trial reference data, not a prescribable regimen. | — |
| Evidence Level | — | — |
Tirzepatide is a 39-amino-acid peptide that activates both the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. It is FDA-approved and marketed by Eli Lilly as Mounjaro for type 2 diabetes (2022) and for chronic weight management (2023), dosed once weekly by subcutaneous injection.
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| Common Side Effects |
| Nausea, Vomiting, Diarrhea, Constipation, Decreased appetite, Elevated resting heart rate |
| — |
Retatrutide (Eli Lilly, compound designation LY3437943) is the first molecule to activate three metabolic receptors at once — GLP-1, GIP, and glucagon. It is still investigational, in Phase 3 trials as of 2026, and is not available through any legal commercial channel.[1][2]
The core difference is one extra receptor. Both drugs use GLP-1 activation to slow gastric emptying and reduce appetite, and GIP activation to amplify glucose-dependent insulin release. Retatrutide layers glucagon receptor agonism on top of that. In the context of GLP-1 co-activation, glucagon receptor agonism increases energy expenditure (resting calorie burn) and drives fatty-acid oxidation in the liver, rather than raising blood sugar the way glucagon does on its own.[1] That added "energy-output" lever is the pharmacological explanation for retatrutide's higher trial weight-loss figures.
| Feature | Retatrutide | Tirzepatide |
|---|---|---|
| Receptors targeted | GLP-1 + GIP + glucagon | GLP-1 + GIP |
| Drug class | Triple incretin agonist | Dual incretin agonist |
| Added lever vs the other | Glucagon (energy expenditure, liver fat) | — |
| Administration | Subcutaneous, once weekly | Subcutaneous, once weekly |
| Developer | Eli Lilly (LY3437943) | Eli Lilly (Mounjaro / Zepbound) |
Both drugs post the highest weight-loss numbers in their respective classes, but they come from different trials at different durations, so any direct percentage comparison is indirect.
In the Phase 2 obesity trial published in the New England Journal of Medicine, retatrutide at 12 mg produced a mean weight loss of ~24.2% at 48 weeks, with roughly 83% of participants losing at least 15% of body weight.[2] In the Phase 3 SURMOUNT-1 trial, tirzepatide at 15 mg produced ~22.5% mean weight loss at 72 weeks, with about 57% of participants losing at least 20%.[3]
| Efficacy measure | Retatrutide | Tirzepatide |
|---|---|---|
| Peak mean weight loss | ~24.2% (12 mg, 48 wk) | ~22.5% (15 mg, 72 wk) |
| Trial phase | Phase 2 | Phase 3 (SURMOUNT-1) |
| Highest dose studied | 12 mg weekly | 15 mg weekly |
| Cardiovascular-outcomes data | None yet | SURPASS-CVOT ongoing |
| FDA status | Investigational | Approved |
The honest read: retatrutide's ceiling looks higher, but tirzepatide's number is confirmed in a large Phase 3 program while retatrutide's is Phase 2. Many drugs with strong Phase 2 results show smaller effects (or fail) in Phase 3. Cross-trial comparisons cannot establish that retatrutide is definitively "better."
Both drugs share the gastrointestinal side-effect pattern common to the GLP-1 class — nausea, vomiting, diarrhea, and constipation — concentrated during the dose-escalation phase and generally dose-dependent.[2][3]
The critical asymmetry is data maturity: tirzepatide has years of post-marketing surveillance across millions of patients, while retatrutide's safety picture rests on Phase 2 trials of limited duration.
This is where the two diverge most sharply.
Any source claiming to sell retatrutide is operating outside the law, and the product may be mislabeled or counterfeit. See our guide on where retatrutide stands and how it compares for the current status.
If you are choosing a treatment you can actually start, the comparison is straightforward: tirzepatide is the option that exists, is approved, and has mature safety and efficacy data. It is a reasonable first-line incretin therapy for obesity or type 2 diabetes when prescribed and monitored by a clinician.
Retatrutide is the more powerful mechanism on paper and the most closely watched compound in the obesity pipeline, but it is not a choice you can make today — it is investigational, and its long-term safety and cardiovascular effects are unknown. If the triple-agonist mechanism interests you, the only path is a clinical trial, and any decision belongs in a conversation with your provider.
For deeper dives, see the full retatrutide profile, the tirzepatide profile, and — if you're comparing the approved options — semaglutide vs tirzepatide.
This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting any peptide therapy. Regulatory status may change.