Tirzepatide vs retatrutide: the approved dual-agonist vs the investigational triple
Tirzepatide is the heaviest-hitting approved obesity drug today. Retatrutide's Phase 2 numbers push even further. Here's what's known, what's not, and what the Phase 3 TRIUMPH readouts could change.
Tirzepatide and retatrutide are both Eli Lilly peptides engineered to activate multiple incretin/metabolic receptors with one molecule. Tirzepatide is a dual GIP / GLP-1 agonist and is FDA-approved for obesity (Zepbound) and T2D (Mounjaro). Retatrutide adds glucagon-receptor agonism — a triple-agonist — and is in Phase 3 as of April 2026. If approved, retatrutide could replace tirzepatide as the efficacy leader, but the clinical case is still being built.
| Field | Tirzepatide | Retatrutide |
|---|---|---|
| Brand names | Mounjaro, Zepbound | LY-3437943 |
| Manufacturer | Eli Lilly | Eli Lilly |
| FDA approved | 2022 (T2D), 2023 (obesity) | Investigational (Phase 3) |
| Indication | Type 2 diabetes, chronic weight management, OSA (2024) | Chronic weight management, T2D (pending) |
| Mechanism | Dual GIP / GLP-1 receptor agonist | Triple GIP / GLP-1 / glucagon receptor agonist |
| Delivery | Once-weekly subcutaneous injection | Once-weekly subcutaneous injection |
| Avg weight loss | ~20.9% at 72 weeks (SURMOUNT-1, 15 mg) | ~24.2% at 48 weeks (Phase 2, 12 mg) |
Primary sources
- Tirzepatide: SURMOUNT-1 (NEJM, 2022)
- Retatrutide: Phase 2 retatrutide trial (NEJM, 2023)
Frequently asked
Is retatrutide better than tirzepatide?
On early evidence, retatrutide produced larger mean weight loss at shorter durations in Phase 2. Phase 3 TRIUMPH data will clarify whether this holds up at 72-week durations and what the side-effect profile looks like at scale.
When will retatrutide be FDA approved?
Eli Lilly has indicated expected approval timing in 2026-2027 contingent on positive Phase 3 readouts. Exact timing depends on filing and FDA review.
Does the added glucagon receptor activity raise side-effect concerns?
Glucagon typically raises blood sugar, which would be a concern in diabetes, but the combined GLP-1 + GIP + glucagon activation in retatrutide has not shown clinically concerning hyperglycemia in Phase 2 data. Longer trials will confirm.
Can I get retatrutide now?
No. It's not FDA approved, not available through legal compounding, and research-peptide vendors selling 'retatrutide' have been subjects of FDA warning letters. Tirzepatide is the closest approved option.