Semaglutide, Tirzepatide and Retatrutide are supplied strictly as laboratory research materials. They are not approved, intended or authorised for human consumption or any therapeutic use in this context. This article is written for qualified researchers and is not medical advice.
One class, three generations
The incretin story is one of adding receptors. Every compound here works by mimicking gut hormones that the body releases after eating — but each generation recruits one more receptor than the last, and the data has tracked that expansion almost linearly. If you want the mechanistic detail behind each target, our explainer on GLP-1 vs GIP vs glucagon agonists unpacks what each receptor actually does. Here we put the three flagship molecules side by side.
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Receptor targets | GLP-1 (single) | GIP + GLP-1 (dual) | GIP + GLP-1 + glucagon (triple) |
| Developer / code | Novo Nordisk | Eli Lilly (LY3298176) | Eli Lilly (LY3437943) |
| Brand names | Ozempic / Wegovy | Mounjaro / Zepbound | None (investigational) |
| Headline trial result | ~15% body-weight reduction (STEP) | ~22.5% body-weight reduction (SURMOUNT-1) | ~24.2% body-weight reduction (TRIUMPH-1) |
| Approx. half-life | ~7 days | ~5 days | ~6 days |
| Regulatory status | FDA-approved | FDA-approved | Investigational |
Semaglutide: the single-agonist benchmark
Semaglutide (Novo Nordisk, marketed as Ozempic and Wegovy) is the compound that made the whole class famous. It is a pure GLP-1 receptor agonist — one target, done exceptionally well. In the STEP programme it produced roughly 15% mean body-weight reduction, a figure that redefined what pharmacology could achieve and set the benchmark everything since has been measured against. Its ~7-day half-life supports once-weekly dosing, and it remains the most widely studied molecule in the family. In a research setting it is the natural reference point: the single-receptor baseline against which dual and triple agonism are judged.
Tirzepatide: adding GIP
Tirzepatide (Eli Lilly, code LY3298176, sold as Mounjaro and Zepbound) was the first to prove that two receptors beat one. It is a dual GIP and GLP-1 agonist, and the addition of GIP appears to amplify the metabolic signal rather than simply duplicate it. In SURMOUNT-1 it reached approximately 22.5% body-weight reduction — a step-change over single-agonist semaglutide that validated the entire multi-agonist thesis. Its half-life of around 5 days again suits weekly dosing. Tirzepatide is the molecule that turned "add another receptor" from a hypothesis into a strategy, and it is now FDA-approved on the strength of that data.
Retatrutide: the triple agonist
Retatrutide (Eli Lilly, code LY3437943) is the current frontier. It layers a third target — glucagon — on top of GIP and GLP-1, making it the only triple agonist of the three. The glucagon arm is thought to raise energy expenditure alongside the appetite and glucose effects of the other two receptors. In the Phase 2 TRIUMPH-1 research it posted roughly 24.2% body-weight reduction, the largest figure in the class — and, notably, the curve had not plateaued when the trial period ended. Retatrutide remains investigational: it is not an approved medicine anywhere and is supplied only as a research reagent. Its ~6-day half-life sits neatly between the other two.
What the differences mean in a research context
Read down the table and the pattern is hard to miss: more receptors, more effect. Semaglutide's ~15% became Tirzepatide's ~22.5% became Retatrutide's ~24.2%, tracking almost exactly the move from one target to two to three. That is not a coincidence — it is the core hypothesis of the field playing out in the data.
But the numbers deserve a caveat researchers should hold onto. These headline figures come from different trials, different populations, different durations and different protocols. STEP, SURMOUNT-1 and TRIUMPH-1 were never designed to be compared head-to-head, so the percentages describe a trend, not a controlled ranking. The gap between Tirzepatide and Retatrutide in particular is narrower than the gap between Semaglutide and Tirzepatide — and Retatrutide's status as an investigational compound means its profile is still being written, while the two dual/single agonists carry mature, FDA-approved datasets.
For research purposes, the three compounds are best understood as a controlled series: change the number of receptors, watch what changes downstream. That is precisely why all three are studied side by side rather than in isolation — and why the "reta vs tirz vs sema" question is really a question about how far adding receptors can go. For a closer look at the top of that ladder, our Retatrutide vs Tirzepatide (2026) comparison narrows the field to the two frontrunners.
The bottom line
Semaglutide set the benchmark with one receptor, Tirzepatide raised it with two, and Retatrutide currently sits highest with three. Each generation added a target and lifted the ceiling — a clean illustration of the multi-agonist thesis. For research-grade material, see our dedicated pages to buy Retatrutide UK, buy Tirzepatide UK, and buy Semaglutide UK, each ≥99% purity with a COA.