Tirzepatide activates two receptors and retatrutide activates three. In published trials retatrutide reaches larger weight reductions, but the figures come from separate studies with different durations and populations, so they do not constitute a direct comparison.
What is the mechanistic difference between the two compounds?
Tirzepatide is a dual agonist: it activates the receptors for glucose-dependent insulinotropic polypeptide, known as GIP, and glucagon-like peptide-1, known as GLP-1. Retatrutide adds a third receptor, that of glucagon, and is therefore described as a triple agonist.
The difference is not merely additive. The GIP and GLP-1 axes act chiefly on intake and glucose handling. Glucagon receptor activation introduces an energy expenditure component, a mechanism distinct from appetite reduction.
What does published tirzepatide evidence show?
The reference obesity study is SURMOUNT-1, a randomised placebo-controlled phase 3 trial with 2,539 participants over 72 weeks.(1)
| Group | Mean weight change |
|---|---|
| Tirzepatide 5 mg | −15.0% |
| Tirzepatide 10 mg | −19.5% |
| Tirzepatide 15 mg | −20.9% |
| Placebo | −3.1% |
89% of participants on 5 mg and 96% on 10 and 15 mg achieved at least 5% body weight reduction, against 28% in the placebo group.
What does published retatrutide evidence show?
Retatrutide has a published phase 2 trial and a phase 3 with reported results. The phase 2, led by Jastreboff and colleagues, enrolled 338 adults and showed a mean reduction of 17.5% at 24 weeks with the 12 mg dose, against 1.6% with placebo.(2)
Phase 3 TRIUMPH-1 extended duration to 80 weeks with 2,339 participants randomised to 4 mg, 9 mg, 12 mg or placebo.(3)
| Group | Mean weight change |
|---|---|
| Retatrutide 4 mg | −19.0% |
| Retatrutide 9 mg | −25.9% |
| Retatrutide 12 mg | −28.3% |
Why do these figures not constitute a direct comparison?
This is the central methodological point of the article. No published head-to-head trial exists between tirzepatide and retatrutide in obesity. Placing both tables side by side invites a conclusion the data do not support with the rigour it appears to have.
Differences preventing direct comparison
- Different duration: 72 weeks in SURMOUNT-1 against 80 weeks in TRIUMPH-1. Eight additional weeks favour the latter, since the weight loss curve has not fully plateaued.
- Different populations: inclusion criteria, baseline weight and demographic composition are not identical across trials.
- Different estimands: how treatment discontinuations and missing data are handled appreciably influences the final published figure.
- Different timing: the trials ran in different periods, with concomitant management standards that may vary.
The defensible reading is that both compounds show weight reductions greater than GLP-1 agonists in monotherapy, and that available evidence suggests a difference favouring retatrutide. The exact magnitude of that difference cannot be established without a direct comparative trial.
What differences exist in the adverse event profile?
In both programmes the most frequent adverse events were gastrointestinal: nausea, diarrhoea, vomiting and constipation. They occurred predominantly during dose escalation and declined over time.
The glucagon receptor agonism component introduces additional considerations, including heart rate increases observed in retatrutide trials. Full characterisation of the long-term safety profile depends on phase 3 programme follow-up.
What is the regulatory status of each compound?
Tirzepatide holds regulatory approval in multiple jurisdictions for specific indications. Retatrutide is in clinical development and holds no approval for clinical use.
Neither compound, in its research-grade presentation, holds INVIMA registration in Colombia. Research-grade material is not intended for medical, diagnostic or therapeutic use, regardless of the molecule's regulatory status in other jurisdictions.
References
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205-216. DOI: 10.1056/NEJMoa2206038. ClinicalTrials.gov: NCT04184622. PMID: 35658024.
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514-526. DOI: 10.1056/NEJMoa2301972. ClinicalTrials.gov: NCT04881760. PMID: 37366315.
- TRIUMPH-1 phase 3 trial. ClinicalTrials.gov: NCT05929066. Results reported at 80 weeks in 2,339 participants.
