Retatrutide, tirzepatide and semaglutide belong to the same agonist family but sit at three different points in development and carry three different receptor profiles. Two of them are approved prescription medicines, one is still an investigational compound. This article walks through five differences researchers and clinicians keep coming back to.
This is not a clinical guide and does not recommend any of these substances for medical use. Retatrutide as supplied by NorexBio is research-grade peptide for in vitro laboratory and analytical research, not for clinical use.
1. Receptor profile: mono-, dual- and triple agonism
The most fundamental difference sits at the molecular level. Semaglutide is a mono-agonist binding and activating the GLP-1 receptor (GLP-1R). Tirzepatide is a dual agonist that adds the GIP receptor (GIPR). Retatrutide is a triple agonist that further adds the glucagon receptor (GCGR).
Each added arm engages a different physiological pathway: GLP-1R drives the insulinotropic response and appetite signalling, GIPR touches adipose and insulin-related pathways, and GCGR engages hepatic glucose output and energy expenditure. That combination is the hypothesis behind retatrutide's development.
2. Regulatory status: two approved, one in phase 3
Semaglutide is approved globally under the brand names Ozempic (type 2 diabetes) and Wegovy (obesity). Tirzepatide is approved as Mounjaro (EU, T2D and obesity) and Zepbound (US, obesity). Both are prescription medicines in the EU and the United States.
Retatrutide is still an investigational compound in Eli Lilly's TRIUMPH phase 3 program. No approvals in the EU, the UK, or the United States. This is the single most important regulatory difference: the distribution context is entirely different, and every clinical claim about retatrutide has to be read with the phase 3 results in mind.
3. Published weight-reduction figures: 14.9% vs 20.9% vs 24.2%
The headline numbers from the most-cited clinical trials: semaglutide produced 14.9% weight reduction at 68 weeks (STEP-1, Wilding et al., NEJM 2021, phase 3, 2.4 mg). Tirzepatide produced 20.9% at 72 weeks (SURMOUNT-1, Jastreboff et al., NEJM 2022, phase 3, 15 mg). Retatrutide produced 24.2% at 48 weeks (Jastreboff et al., NEJM 2023, phase 2, 12 mg).
These figures are not directly comparable: the trials run for different durations, use different doses, and sit at different development stages. The retatrutide number comes from phase 2 and can shift in phase 3. The semaglutide and tirzepatide numbers come from phase 3 pivotal trials and have already passed regulatory review.
4. Dosing schedule: weekly subcutaneous, but peak doses differ
All three are given as a once-weekly subcutaneous injection with a titration ramp over several weeks. The peak doses in the cited trials differ: semaglutide 2.4 mg/week, tirzepatide 15 mg/week, retatrutide 12 mg/week. Doses are not directly comparable across molecules because receptor affinity and pharmacokinetics differ.
For research contexts, dosing is reasoned per molecule, not per class. Retatrutide research pens are pre-filled and stability- tested at specific strengths (6, 15 and 30 mg) rather than at clinical titration steps.
5. Use context: clinical vs in vitro research
Semaglutide and tirzepatide flow through a clinical supply chain: pharmacy dispensing, prescriptions, documented patient follow-up. Retatrutide as supplied by NorexBio flows through a research supply chain: research-grade peptide, in vitro laboratory use, no clinical application.
That distinction is what lets retatrutide be studied academically and industrially in in vitro models while its clinical development continues in parallel. Anyone looking for an approved prescription treatment should discuss semaglutide and tirzepatide with a clinician.
Summary
Five differences, five layers: receptor profile, approval status, published effect sizes, dosing schedule, and use context. The primary literature behind the effect figures is summarised on our science page, and the retatrutide research-pen specifications live on the quality page.