The smallest gap in the GLP class — retatrutide's triple agonism adds ~2–4 percentage points over tirzepatide's dual agonism. Critical caveat: tirzepatide's data is Phase 3; retatrutide's is Phase 2 only.
Tirzepatide's ~20–22% weight loss comes from SURMOUNT-1 Phase 3 (n=2,539, 72 weeks). Retatrutide's ~24.2% comes from a Phase 2 trial (n=338, 48 weeks). Phase 2 trials enroll smaller, more selected populations and typically show higher efficacy than Phase 3. The TRIUMPH Phase 3 program is ongoing — final weight loss figures may be lower than 24.2%.
| Timepoint | Tirzepatide | Retatrutide |
|---|---|---|
| Week 4 | ~2–3% | ~2–4% |
| Week 12 | ~6–8% | ~7–10% |
| Week 24 | ~12–14% | ~14–17% |
| Week 36 | ~16–18% | ~19–22% |
| Week 48 | ~18–20% | ~24.2% (Phase 2 endpoint) |
| Week 72 | ~20–22% (SURMOUNT-1) | Phase 3 data pending |
| Parameter | Tirzepatide | Retatrutide |
|---|---|---|
| Receptor mechanism | GLP-1 + GIP (dual agonist) | GLP-1 + GIP + Glucagon (triple) |
| Average weight loss (max dose) | ~20–22% (15 mg, SURMOUNT-1, Ph3) | ~24.2% (12 mg, Phase 2) |
| Average weight loss (mid dose) | ~17–19% (10 mg, SURMOUNT-1) | ~17.3% (4 mg, Phase 2) |
| Data phase | Phase 3 (SURMOUNT program) | Phase 2 only (TRIUMPH ongoing) |
| Trial duration | 72 weeks (SURMOUNT-1) | 48 weeks (Phase 2) |
| FDA approval status | Approved (Mounjaro/Zepbound) | Not approved (est. 2027–2028) |
| Nausea rate (therapeutic dose) | 33–45% | ~47–58% (Phase 2) |
| GI discontinuation rate | ~5–8% | Phase 2 data pending Ph3 |
| Half-life | ~5 days (weekly injection) | ~6 days (weekly injection) |
| Cardiovascular outcome data | SURPASS-CVOT (ongoing) | No CV outcome data yet |
| Long-term safety data | 3+ years real-world data | Phase 2 only (limited) |
| Research-grade availability | Available (Purgo Labs) | Available (Purgo Labs) |
In available data, yes — retatrutide 12 mg produced ~24.2% weight loss at 48 weeks in Phase 2, compared to tirzepatide 15 mg ~20–22% at 72 weeks in SURMOUNT-1 (Phase 3). However, this comparison has a critical caveat: retatrutide's data is Phase 2 only, while tirzepatide's is Phase 3. Phase 2 trials typically show higher efficacy than Phase 3 in broader populations. The gap may narrow when retatrutide's TRIUMPH Phase 3 results are published (expected 2025–2026).
In current data, retatrutide 12 mg produces approximately 2–4 percentage points more weight loss than tirzepatide 15 mg: ~24.2% vs ~20–22%. This is the smallest gap in the GLP class — semaglutide vs retatrutide (~15% vs ~24%) shows a much larger difference. For a 100 kg person, the tirzepatide vs retatrutide gap translates to roughly 2–4 kg additional loss with retatrutide. Phase 3 data may narrow or eliminate this gap.
Retatrutide is a triple agonist (GLP-1 + GIP + glucagon), while tirzepatide is a dual agonist (GLP-1 + GIP). The additional glucagon receptor agonism in retatrutide increases energy expenditure through thermogenesis, promotes fat oxidation, and reduces hepatic fat accumulation. This third mechanism adds to the appetite and insulin effects of GLP-1/GIP dual agonism. The glucagon component is the key differentiator between the two compounds.
Tirzepatide's ~20–22% weight loss comes from SURMOUNT-1, a Phase 3 trial (n=2,539, 72 weeks). Retatrutide's ~24.2% comes from a Phase 2 trial (n=338, 48 weeks). Phase 2 trials are smaller, shorter, and enroll more homogeneous populations — they typically show higher efficacy than Phase 3 results in broader real-world populations. Retatrutide's TRIUMPH Phase 3 program is ongoing with results expected 2025–2026. The final Phase 3 weight loss figure may be lower than 24.2%.
Tirzepatide has a nausea rate of ~33–45% at therapeutic doses. Retatrutide showed ~47–58% nausea in Phase 2 at the 12 mg dose — higher than tirzepatide, likely due to the addition of glucagon receptor agonism which has independent GI effects. Despite producing similar weight loss, retatrutide appears to have a worse GI tolerability profile than tirzepatide based on Phase 2 data.
No. As of April 2026, retatrutide is not FDA approved. Phase 3 TRIUMPH trials are ongoing with primary completion expected 2025–2026. An NDA submission is estimated for 2026–2027, with potential FDA approval in 2027–2028. Tirzepatide (Mounjaro) was FDA approved for T2D in May 2022 and (Zepbound) for obesity in November 2023.
Yes. Research-grade tirzepatide and retatrutide are available from verified suppliers like Purgo Labs for in vitro and preclinical research purposes. This is distinct from FDA-approved Mounjaro and Zepbound (tirzepatide), which require a prescription. Purgo Labs' research-grade compounds come with third-party COAs from accredited US labs confirming ≥99% purity.
Purgo Labs provides pharmaceutical-grade tirzepatide and retatrutide with third-party COAs confirming ≥99% purity. Use code HEALTH for 15% off.
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