Semaglutide engages one receptor — GLP-1 — and is the reference compound for the whole incretin class. Retatrutide (LY3437943) engages three: GLP-1, GIP, and glucagon, from a GIP-based backbone. One is an approved medicine from Novo Nordisk; the other is an investigational Eli Lilly compound in Phase 3. This is a pharmacological and structural comparison for research context — it does not compare human outcomes or make suitability claims.
Side by side
| Semaglutide | Retatrutide (LY3437943) | |
|---|---|---|
| Receptor targets | GLP-1 only (mono-agonist) | GIP + GLP-1 + glucagon (triple agonist) |
| Developer | Novo Nordisk | Eli Lilly |
| Peptide backbone | GLP-1 analogue | GIP-based, non-coded substitutions |
| Design philosophy | Optimise the single best-validated target | Layer three complementary pathways |
| Half-life extension | C18 fatty-diacid acylation | C20 fatty-diacid, albumin binding |
| Approx. molecular weight | ~4,114 Da | ~4,731 Da |
| Dosing cadence (clinical) | Once weekly (injection); daily oral form exists | Once weekly (trials) |
| Regulatory status | Approved medicine (MHRA, FDA) | Investigational — Phase 3, no approval anywhere |
Two opposite answers to the same design question
The comparison is interesting because the molecules embody opposing philosophies. Semaglutide bets everything on the single best-validated target in metabolic pharmacology and optimises it relentlessly — one receptor, a true GLP-1 analogue, and the simplest story in the class. Retatrutide bets that breadth beats depth: keep the GLP-1 arm as the shared baseline, add the second incretin axis (GIP), then add a third, mechanistically distinct pathway at the glucagon receptor. Every question about how the two compounds differ ultimately reduces to what those two extra receptors contribute — which is the subject of our mechanism of action explainer.
Structurally they are further apart than the marketing shorthand suggests: retatrutide is not a “stronger semaglutide” but a different backbone lineage — GIP-based, like tirzepatide, with non-coded amino-acid substitutions. What the compounds share is the half-life strategy (fatty-acid acylation driving albumin binding, enabling weekly dosing) and the GLP-1 arm that makes them comparable at all. Retatrutide’s published trial figures are summarised in our clinical trial evidence overview — separate-population findings, not a head-to-head against semaglutide.
Frequently asked questions
What is the difference between retatrutide and semaglutide?
They sit at opposite ends of the incretin design spectrum. Semaglutide is a GLP-1 analogue engaging one receptor — the simplest, best-validated pharmacology in the class and its reference point. Retatrutide engages three receptors (GIP, GLP-1, and glucagon) from a GIP-based backbone. They also come from different companies and different stages: semaglutide is an approved medicine, while retatrutide is investigational and approved nowhere.
Is retatrutide the same kind of drug as semaglutide?
They belong to the same broad family — long-acting incretin-receptor peptide agonists using fatty-acid acylation for once-weekly dosing — but not the same subclass. Semaglutide is a GLP-1 mono-agonist; retatrutide is a triple agonist whose GIP-based backbone is chemically closer to tirzepatide than to semaglutide. The shared GLP-1 arm is why the compounds are compared at all; the other two arms are why the comparison has limits.
Is retatrutide more effective than semaglutide (Wegovy/Ozempic)?
No responsible head-to-head answer exists: the two compounds have never been compared directly in a published trial, and cross-trial comparisons involve different populations, designs, and endpoints. Retatrutide’s own trial figures — Phase 2 (NEJM 2023) and Phase 3 TRIUMPH-1 (2026) — are summarised with attribution in our clinical evidence overview, as research findings rather than product claims. Semaglutide’s efficacy is documented in its own approved labelling.
Why does retatrutide target receptors semaglutide ignores?
Semaglutide validated the GLP-1 axis; the field then asked what additional pathways could add. The GIP arm (proven by tirzepatide) contributes a second incretin axis, and the glucagon arm — retatrutide’s distinguishing feature — is associated in research with energy expenditure and hepatic glucose and fat handling. Whether stacking all three is better engineering or added complexity is precisely what the ongoing clinical programme exists to answer.
Are semaglutide and retatrutide both available in the UK?
In completely different senses. Semaglutide is a licensed prescription medicine available through the NHS and private prescribers. Retatrutide has no marketing authorisation anywhere and cannot be prescribed; it exists in the UK only as a research compound. RETApro supplies retatrutide strictly for laboratory research use and does not sell semaglutide.