---
title: "Retatrutide vs tirzepatide: Trial Data Side by Side"
url: https://www.primaralabs.com/research/compare/retatrutide-vs-tirzepatide
source: Primara Labs, markdown mirror of the HTML page
---

# Retatrutide vs tirzepatide

As of 23 September 2026 no head-to-head trial of retatrutide against tirzepatide has reported. The trials below are set side by side from separate studies, which is not a head-to-head result.

Primara Labs sells some of the compounds covered here. Every figure on this page links to its source and the date it was checked.

Updated 24 September 2026

Retatrutide vs Tirzepatide vs Semaglutide: Trials Compared (PH)1:55·[Transcript and chapters](https://www.primaralabs.com/videos/reta-vs-tirz-vs-sema)

Mechanism

## How the two differ

### Retatrutide

Retatrutide is a single peptide that activates three receptors: GIP, GLP-1 and glucagon. Lilly describes it as a first-in-class triple hormone receptor agonist.

[Source](https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-successful-two-additional) · checked 23 September 2026

### Tirzepatide

Tirzepatide is a single peptide that activates two receptors: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1.

[Source](https://doi.org/10.1056/NEJMoa2206038) · checked 23 September 2026

Cross-trial

## Separate trials, side by side

Choose two to four trials

2 selected.

Mean percent change in body weight by arm, as each source reports it. Navy bars are the trial arms, grey bars the comparator. Bars from different trials are not a head-to-head comparison: populations, durations and estimands differ.

|  | [TRIUMPH-1](https://www.primaralabs.com/research/trials/triumph-1) | [SURMOUNT-1](https://www.primaralabs.com/research/trials/surmount-1) |
| --- | --- | --- |
| Compound | Retatrutide | Tirzepatide |
| Phase | 3 | 3 |
| Population | Adults with obesity, or overweight with at least one weight-related condition, without diabetes | Adults with BMI of 30 or more, or 27 or more with at least one weight-related complication, excluding diabetes |
| n | 2,339 | 2,539 |
| Weeks | 80 | 72 |
| Estimand | efficacy | treatment-regimen |
| Arms | 4 mg: -19.0%; 9 mg: -25.9%; 12 mg: -28.3% | 5 mg: -15.0%; 10 mg: -19.5%; 15 mg: -20.9% |
| Comparator | Placebo: -2.2% | Placebo: -3.1% |
| Stopped for adverse events | 4 mg: 4.1%; 9 mg: 6.9%; 12 mg: 11.3%; Placebo: 4.9% | 5 mg: 4.3%; 10 mg: 7.1%; 15 mg: 6.2%; Placebo: 2.6% |
| Source | Eli Lilly topline release, 21 May 2026 | Jastreboff AM et al. N Engl J Med 2022;387:205-216 |

TRIUMPH-1: side effects reported

In TRIUMPH-1, discontinuation because of adverse events was 4.1% on 4 mg, 6.9% on 9 mg and 11.3% on 12 mg, against 4.9% on placebo. The most frequently reported adverse events were nausea in 28.6% on 4 mg, 38.4% on 9 mg and 42.4% on 12 mg against 14.8% on placebo, diarrhoea in 25.2% on 4 mg, 34.1% on 9 mg and 32.0% on 12 mg against 13.5% on placebo, constipation in 23.8% on 4 mg, 25.9% on 9 mg and 26.1% on 12 mg against 10.9% on placebo and vomiting in 10.6% on 4 mg, 22.8% on 9 mg and 25.3% on 12 mg against 4.8% on placebo.

SURMOUNT-1: side effects reported

In SURMOUNT-1, discontinuation because of adverse events was 4.3% on 5 mg, 7.1% on 10 mg and 6.2% on 15 mg, against 2.6% on placebo.

Figures from different trials are not a head-to-head comparison: the populations, durations and estimands differ. The head-to-head trials among these compounds are SURMOUNT-5, tirzepatide against semaglutide, completed, and TRIUMPH-5, retatrutide against tirzepatide, still running.

TRIUMPH-5 is a phase 3 trial of retatrutide against tirzepatide in adults who have obesity, registered as NCT06662383 and not yet reported (ClinicalTrials.gov, checked 23 September 2026). [Trial page](https://www.primaralabs.com/research/trials/triumph-5).

Questions

## Questions

### Has retatrutide been compared head to head with tirzepatide?

TRIUMPH-5 is a phase 3 trial of retatrutide against tirzepatide in adults who have obesity, registered as NCT06662383 and not yet reported (ClinicalTrials.gov, checked 23 September 2026).

### Why can the TRIUMPH-1 and SURMOUNT-1 figures not be compared directly?

Figures from different trials are not a head-to-head comparison: the populations, durations and estimands differ. The head-to-head trials among these compounds are SURMOUNT-5, tirzepatide against semaglutide, completed, and TRIUMPH-5, retatrutide against tirzepatide, still running. TRIUMPH-1 reports the efficacy estimand over 80 weeks. SURMOUNT-1 reports the treatment-regimen estimand over 72 weeks.