4 February 20257 min read

Retatrutide vs Tirzepatide: 2025 Trial Data Compared

Retatrutide and tirzepatide are two of the most talked-about metabolic research compounds of the decade. Both target incretin pathways, both have produced striking trial results, and both are frequently compared by Australian researchers trying to understand where the field is heading. This guide summarises the published data through 2025 — without the hype.

The short version

Tirzepatide is a dual agonist (GLP-1 + GIP). Retatrutide is a triple agonist (GLP-1 + GIP + glucagon). The addition of glucagon-receptor activity is what separates retatrutide's metabolic profile from tirzepatide's in published trials.

Mechanism: dual vs triple agonism

Tirzepatide binds and activates both the GLP-1 and GIP receptors. GLP-1 activity drives satiety, slows gastric emptying and improves insulin response. GIP activity contributes additively to glucose handling and appears to soften GLP-1-related side effects.

Retatrutide adds glucagon-receptor agonism on top. The glucagon component is associated with increased energy expenditure and hepatic lipid mobilisation in published animal and human studies — a profile distinct from pure GLP-1 or dual GLP-1/GIP molecules.

Phase 2 trial results

Tirzepatide (SURMOUNT-1, 2022): mean body-weight reduction of ~20.9% at 72 weeks on the 15 mg dose, in adults with obesity without diabetes.
Retatrutide (Phase 2, NEJM 2023): mean body-weight reduction of ~24.2% at 48 weeks on the 12 mg dose. Notably, the trajectory had not plateaued at 48 weeks — suggesting longer dosing windows may yield further change.

Direct head-to-head trials have not been published. Comparing across separate studies is imperfect, but the magnitude difference is hard to ignore.

Side-effect profiles

Both research compounds share the GLP-1-class profile: nausea, transient GI effects and slowed gastric emptying, most pronounced during dose escalation. Retatrutide's glucagon component has been associated with mild elevations in heart rate in some trial arms. Long-term safety data on retatrutide is still accumulating.

Half-life and dosing cadence

Tirzepatide: ~5 days. Once-weekly subcutaneous administration is the trial standard.
Retatrutide: ~6 days. Also once-weekly in published trials.

What this means for research

Retatrutide is, by published evidence, the more potent metabolic research compound of the two — but it's also earlier in clinical development. Tirzepatide has a larger and more mature dataset. Researchers comparing the two should weigh both the magnitude of effect and the depth of long-term safety data.

For Australian researchers sourcing material, see our Retatrutide 10mg listing and the full retatrutide research guide.