Comparison
Reta vs Tirzepatide
Published · Reviewed
Retatrutide (LY-3437943) is an investigational GLP-1 / GIP / glucagon triagonist; tirzepatide is an approved GLP-1 / GIP dual agonist. That receptor difference is established, but outcome figures come from separate trials with different populations and durations. This page compares the evidence without treating cross-trial numbers as a head-to-head result.
For in-vitro laboratory research only. Not for human or veterinary use.
The shape of the comparison
Both are once-weekly subcutaneous peptides in the cited studies. Tirzepatide activates GLP-1 and GIP receptors. Retatrutide activates those receptors plus the glucagon receptor. The additional target is a mechanistic distinction; it should not be used by itself to assign the difference between outcomes observed in separate clinical programs.
Receptor design at a glance
| Reta | Tirzepatide | |
|---|---|---|
| GLP-1 receptor | Agonist | Agonist |
| GIP receptor | Agonist | Agonist |
| Glucagon receptor | Agonist | — |
| Class | Triagonist | Dual agonist |
| Developer | Eli Lilly (LY-3437943) | Eli Lilly (LY-3298176) |
| CAS number | 2381089-83-2 | 2023788-19-2 |
Headline weight-loss readouts
The figures below are sourced trial results, not a head-to-head comparison. Population, endpoint, duration, protocol and estimand differ. TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 and TRIUMPH-4 were company topline disclosures at the July 28, 2026 review; the Phase 2 retatrutide and SURMOUNT-1 rows are peer-reviewed publications.
| Trial / phase | Population | Compound & study dose | Window / endpoint | Reported mean change | Primary source |
|---|---|---|---|---|---|
| SURMOUNT-1 Phase 3 NCT04184622 | Obesity or overweight with a related complication; no diabetes | Tirzepatide 15 mg | 72 weeks; percent change from baseline | −20.9% | NEJM, 2022 |
| Retatrutide obesity trial Phase 2 NCT04881760 | Obesity or overweight with a related condition; no diabetes | Retatrutide 12 mg | 48 weeks; least-squares mean change | −24.2% | NEJM, 2023 |
| TRIUMPH-4 Phase 3 NCT05931367 | Obesity or overweight with knee osteoarthritis; no diabetes | Retatrutide 12 mg | 68 weeks; efficacy estimand | −28.7% | Lilly topline, 11 Dec 2025 |
| TRIUMPH-1 Phase 3 NCT05929066 | Obesity or overweight; master trial | Retatrutide 12 mg | 80 weeks; efficacy estimand | −28.3% | Lilly topline, 21 May 2026 |
| TRIUMPH-2 Phase 3 NCT05929079 | Obesity or overweight with type 2 diabetes | Retatrutide 12 mg | 80 weeks; efficacy estimand | −20.8% | Lilly topline, 23 Jul 2026 |
| TRIUMPH-3 Phase 3 NCT05882045 | Severe obesity and established cardiovascular disease, with or without type 2 diabetes | Retatrutide 12 mg | 80 weeks; efficacy estimand | −22.6% | Lilly topline, 23 Jul 2026 |
No row above is a direct retatrutide-versus-tirzepatide trial. The appropriate conclusion is that each program reported substantial mean changes in its own population and design; the table does not prove that one compound is superior to the other.
Trial-regimen context
The cited retatrutide trials and tirzepatide label use different protocol-defined regimens for different molecules and evidence settings. The outcome table identifies the studied arms, but this page does not reproduce escalation schedules. Those regimens are not interchangeable and are not research-use instructions.
Pharmacokinetics
| Reta | Tirzepatide | |
|---|---|---|
| Half-life | Approximately 6 days | Approximately 5–6 days |
Side-effect profile
Gastrointestinal events, including nausea, diarrhea, vomiting and constipation, were common in the cited programs. Incidence cannot be compared cleanly across separate trials. Tirzepatide has post-approval safety data; retatrutide remains investigational, and detailed Phase 3 publications are still developing.
What this means for a research-context comparison
The evidence supports a clear receptor distinction and a clear status distinction: tirzepatide is approved and has a larger safety evidence base; retatrutide is a triple agonist still under investigation. Separate outcome percentages are useful context, but they do not answer which compound would perform better in the same population under the same protocol.
Primary sources and review date
- Retatrutide Phase 2 obesity trial, NEJM (2023)
- SURMOUNT-1 tirzepatide trial, NEJM (2022)
- TRIUMPH-4 topline disclosure, Lilly (11 December 2025)
- TRIUMPH-1 topline disclosure, Lilly (21 May 2026)
- TRIUMPH-2 and TRIUMPH-3 topline disclosure, Lilly (23 July 2026)
- Tirzepatide US prescribing information, FDA (2026)
Last reviewed: 28 July 2026. Company topline results are identified as such until full peer-reviewed reports are available. Retatrutide remained investigational; Lilly said it planned a US biologics license application in the first quarter of 2027.
For a broader evidence map that adds the amylin pathway, use the Remy Peptides retatrutide, tirzepatide and CagriSema comparison.
For purity verification of reta research material specifically, see the COA library for the current batches: RET-20-C-2604-001 (20mg pen, 99.841% HPLC), RET-20-V-2604-001 (vial record, full panel), and RETP002 (30mg pen). Each record publishes its own Janoshik task number and verification key so the result can be confirmed at the laboratory directly.
Common questions
How does reta (retatrutide) differ mechanistically from tirzepatide?
What's the headline retatrutide vs tirzepatide weight-loss difference in published trials?
Are the trial regimens comparable?
What about half-life?
Which has more side-effect data?
From the comparison to the proof
This page stays with receptor design and trial readouts. To check what an actual Reta batch tests at, open the COA library and read the underlying Janoshik reports, task numbers and verification keys.