Retatrutide (LY3437943) and tirzepatide are two of the most active research peptides in the incretin space. Both have produced striking weight-loss data in clinical trials, but they act on different receptor combinations and have different reported pharmacokinetics. This article compares the two compounds at a mechanistic and trial level for laboratory researchers.
Quick comparison
| Property | Retatrutide | Tirzepatide |
|---|---|---|
| Developer code | LY3437943 | LY3298176 |
| Receptors | GIP + GLP-1 + glucagon (triple) | GIP + GLP-1 (dual) |
| Reported half-life | ~6 days | ~5 days |
| Dosing cadence in trials | Once weekly | Once weekly |
| Phase 2 top-line weight change | ~24% at 48 weeks (12 mg) | ~21% at 72 weeks (15 mg) |
Mechanism of action
Tirzepatide is a dual receptor agonist that binds GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). The GLP-1 arm drives insulin secretion and appetite suppression while the GIP arm appears to modulate adipose tissue handling of nutrients.
Retatrutide adds a third receptor: glucagon. The glucagon receptor contribution is thought to increase resting energy expenditure and lipolysis, which may explain the larger weight-change effect size seen in early trials. The triple-agonist design is novel and is the active area of research that distinguishes retatrutide from earlier compounds.
Published trial data
Retatrutide phase 2 (obesity)
In the phase 2 trial reported in the New England Journal of Medicine in 2023, participants receiving 12 mg weekly retatrutide showed a mean body weight reduction of roughly 24% at 48 weeks, with continued downward trajectory at the data cutoff. Side-effect profile was dominated by mild-to-moderate gastrointestinal events that diminished with dose titration.
Tirzepatide SURMOUNT-1
The SURMOUNT-1 trial reported a mean body weight reduction of approximately 21% at 72 weeks with 15 mg weekly tirzepatide. Tirzepatide is also approved for type 2 diabetes under the SURPASS programme, where A1c reductions of around 2.0-2.5 percentage points were observed at higher doses.
Pharmacokinetics
Both compounds are engineered for once-weekly subcutaneous administration. Tirzepatide uses a C20 fatty diacid linker for albumin binding to extend half-life. Retatrutide also uses albumin-binding chemistry and shows a similar effective half-life of about six days in early reports.
Storage and handling for laboratory use
- Lyophilized peptide: store at -20°C long term, 2-8°C for short term.
- Reconstituted with bacteriostatic water: stable at 2-8°C for approximately 28 days based on bacteriostatic stability data.
- Avoid repeated freeze-thaw cycles; aliquot into small working volumes if performing time-course work.
- See the peptide reconstitution guide for step-by-step bacteriostatic water mixing and dosage math.
Which compound should a research lab choose?
The two are not interchangeable. Tirzepatide has a much larger body of published clinical data, three-receptor selectivity work and a longer post-marketing record. Retatrutide is earlier in its development arc but offers a unique opportunity to study triple-agonist pharmacology and the additive contribution of glucagon receptor activation. Many labs run them in parallel to characterise differential effects on energy expenditure, hepatic glucose output and adipose tissue.
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Browse Research PeptidesReferences
Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity - a phase 2 trial. N Engl J Med 2023; 389:514-526. Jastreboff AM, et al. SURMOUNT-1: tirzepatide once weekly for the treatment of obesity. N Engl J Med 2022; 387:205-216.