Retatrutide and tirzepatide are among the most intensively researched peptides in metabolic and weight research. Both bind to hormone receptors that control energy metabolism – but they differ in the number of receptors addressed and therefore in the activity profile being studied. This article compares the two on the basis of published study data.
Mechanism of action compared
Tirzepatide is a dual agonist: it activates both the GLP-1 receptor (glucagon-like peptide-1) and the GIP receptor (glucose-dependent insulinotropic polypeptide). Both receptors belong to the family of incretin hormones, which research associates with satiety regulation, delayed gastric emptying and improved insulin sensitivity.
Retatrutide goes one step further and is studied as a triple agonist: in addition to GLP-1 and GIP it also activates the glucagon receptor. In preclinical and clinical research this third component is associated with increased energy expenditure and greater fat oxidation in the liver – a mechanism absent from purely dual agonists such as tirzepatide.
State of research
Extensive clinical data are now available for both molecules:
- Tirzepatide was studied in the phase 3 trial SURMOUNT-1 (Jastreboff et al., 2022, published in the New England Journal of Medicine) in 2,539 participants over 72 weeks. Depending on the dose (5/10/15 mg), mean weight reduction was 16.0% to 22.5%, compared with 2.4% on placebo.
- Retatrutide was first studied in a phase 2 trial (Jastreboff et al., 2023, also NEJM) in 338 participants over 48 weeks – with a mean weight reduction of up to 24.2% in the highest dose group (12 mg). In the phase 3 trial TRIUMPH-1 completed since then (topline results May 2026, 2,339 participants, 80 weeks), a mean weight reduction of up to 28.3% was achieved, and up to 30.3% in a pre-specified 104-week extension in participants with a BMI ≥ 35.
Important for interpretation: there is as yet no published head-to-head study comparing both substances in the same trial under identical conditions. The percentages quoted come from separate studies with different designs (including different study durations), so a direct numerical comparison should be interpreted with caution.
Why the third receptor component makes the difference
Physiologically, the glucagon receptor plays a different role from GLP-1 and GIP: while GLP-1 and GIP mainly influence insulin release and satiety, research associates glucagon with a direct increase in resting energy expenditure and increased breakdown of fat stores in the liver. Combined with the appetite-regulating effects of GLP-1/GIP, an additive mechanism is therefore being investigated for retatrutide – more calories burned alongside reduced calorie intake. Whether this theoretical advantage is confirmed in direct comparison studies is the subject of ongoing research.
Approval status
Tirzepatide is approved as a medicinal product in several countries (including the US and the EU). As of July 2026, retatrutide is still in the approval process – according to the manufacturer, a submission to the US regulatory authority is planned for the fourth quarter of 2026. No approval exists in Europe so far. AlpenPeptides offers both molecules exclusively as research peptides for scientific research – not as medicinal products and not for use in humans.
Direct comparison
| Tirzepatide | Retatrutide | |
|---|---|---|
| Receptor activation | GLP-1 + GIP (dual) | GLP-1 + GIP + glucagon (triple) |
| Key study | SURMOUNT-1 (phase 3, NEJM 2022) | Phase 2 (NEJM 2023) + TRIUMPH-1 (phase 3, 2026) |
| Study duration | 72 weeks | 48 weeks (phase 2) / 80 weeks (phase 3) |
| Mean weight reduction (highest dose) | up to 22.5% | up to 28.3% (phase 3) |
| Approval status | approved (incl. US, EU) | in approval process, as of 07/2026 |
Conclusion
Tirzepatide and retatrutide represent two successive generations of incretin research: tirzepatide as a clinically established dual agonist with a broad body of data, retatrutide as a triple agonist with an additional mechanism that increases energy expenditure and promising, but not yet approved, phase 3 data. Which molecule is relevant for a specific research question depends on the mechanism being studied.
Both research peptides are available in our shop – lab-tested and COA-certified: Tirzepatide and Retatrutide.
Sources & further studies
- Jastreboff AM, et al. (2023): Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. DOI: 10.1056/NEJMoa2301972
- Jastreboff AM, et al. (2022): Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. DOI: 10.1056/NEJMoa2206038 (PubMed)
- Eli Lilly and Company (May 2026): Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1, topline results). investor.lilly.com
- Systematic review & network meta-analysis: Beyond GLP-1: efficacy and safety of dual and triple incretin agonists in personalized type 2 diabetes care. Acta Diabetologica. PMC12433336
Note: this article is for information and research purposes only and does not constitute medical advice. Retatrutide and tirzepatide for research are not intended for human consumption or for use in humans.