Semaglutide vs tirzepatide: one receptor or two

The short version

Semaglutide acts on one receptor, GLP-1; tirzepatide acts on two, GIP and GLP-1. They come from different parent hormones: semaglutide is a modified GLP-1, tirzepatide is a modified GIP that has been taught to activate the GLP-1 receptor as well. Both carry a fatty-diacid side chain that binds albumin and gives a half-life of about a week, which is why both are dosed weekly in the clinic. Both are licensed medicines in the UK, which makes this the only comparison in our catalogue between two compounds that each have a full phase 3 record and a direct head-to-head trial in both diabetes and obesity. In those trials tirzepatide produced larger changes in HbA1c and body weight; semaglutide has the longer safety record and the cardiovascular-outcomes evidence in people with obesity. For an in-vitro programme the choice turns on whether the question involves the GIP receptor at all.

Both compounds are supplied by BuyUK Peptides as research chemicals for in-vitro laboratory use only. Trial figures quoted below are facts about the published trials, not guidance of any kind.

Receptors and origin

Semaglutide was designed as a longer-acting successor to liraglutide. The discovery paper by Lau and colleagues describes the three changes to the GLP-1 sequence that make it work: aminoisobutyric acid at position 8 to block cleavage by dipeptidyl peptidase-4, arginine in place of lysine at position 34 so that only one lysine remains for acylation, and a C18 fatty diacid attached to lysine 26 through a γ-glutamate and two short polyethylene-glycol spacers [1]. The diacid binds albumin tightly enough to give a half-life of about 160 hours in humans, roughly seven days.

Tirzepatide started from the other incretin. Coskun and colleagues describe engineering GLP-1 receptor activity into a GIP backbone, with Aib at positions 2 and 13 and a C20 diacid on lysine 20 [2]. The result is a peptide that behaves like native GIP at the GIP receptor and like a weaker, biased agonist at the GLP-1 receptor; Willard and colleagues showed it favours cAMP signalling over β-arrestin recruitment there, with less receptor internalisation than GLP-1 itself produces [3]. The clinical half-life is about five days.

Structure and chemistry

The two are easy to tell apart analytically. Their molecular weights differ by 700 Da, so an LC-MS identity line settles which compound is in the vial without ambiguity. On reversed-phase HPLC tirzepatide, with its longer diacid and larger hydrophobic surface, elutes later than semaglutide under the same gradient. Both are amphipathic because of the lipid tail, and both adsorb to plastics and some filter membranes at low concentration; the practical handling is the same, as set out below.

The head-to-head record

Few pairs of peptides have been compared as directly as these two. SURPASS-2, published in 2021, randomised 1,879 adults with type 2 diabetes to one of three tirzepatide doses or to semaglutide 1 mg once weekly for 40 weeks. All three tirzepatide doses lowered HbA1c and body weight more than semaglutide 1 mg did, with the highest tirzepatide dose producing a mean weight change of about −11.2 kg against −5.7 kg on semaglutide [4]. The comparison has been criticised because semaglutide 2.4 mg, the obesity dose, was not available as a comparator at the time.

SURMOUNT-5 answered that. Published in 2025, it randomised 751 adults with obesity and without diabetes to the maximum tolerated dose of tirzepatide or semaglutide for 72 weeks. Mean weight reduction was 20.2 per cent with tirzepatide and 13.7 per cent with semaglutide, and a larger share of the tirzepatide group reached each weight-loss threshold [5]. Gastrointestinal adverse events were similar in nature and frequency in both arms.

Semaglutide's own record is older and in some respects broader. STEP 1, the 68-week phase 3 obesity trial, reported a mean weight reduction of 14.9 per cent against 2.4 per cent on placebo [6]. SELECT, published in 2023, is the trial tirzepatide has not yet matched: in 17,604 adults with established cardiovascular disease and overweight or obesity but without diabetes, semaglutide reduced the composite of cardiovascular death, myocardial infarction and stroke by 20 per cent relative to placebo over a mean of about 40 months [7]. Tirzepatide's cardiovascular-outcomes trial, SURPASS-CVOT, reported in 2025 that tirzepatide was non-inferior to dulaglutide on major adverse cardiovascular events in type 2 diabetes; the oral formulation of semaglutide has its own cardiovascular trial. Where the two compounds stand on cardiovascular outcomes in obesity will become clearer as the SURMOUNT-MMO trial reports.

Licensing and legal status in the UK

Both are prescription-only medicines authorised by the MHRA. Semaglutide is licensed as Ozempic (type 2 diabetes), Wegovy (weight management) and Rybelsus (an oral tablet for type 2 diabetes); tirzepatide is licensed as Mounjaro for both indications. Both are on the WADA Prohibited List under S4.5 as GLP-1 receptor agonists; both have been the subject of MHRA warnings about counterfeit pens sold online. None of this changes the basis on which research material is supplied: the peptides sold here are chemicals for in-vitro laboratory use, not medicines, and the UK rules on research compounds apply equally to both.

One practical difference follows from licensing. Both compounds have a public reference standard and published pharmacopoeial or regulatory analytical methods, so a certificate of analysis for either can be judged against an external benchmark. That is not true of the unlicensed members of the family such as GLP-3 (retatrutide), survodutide and mazdutide.

Handling at the bench

The two are handled identically. Both are supplied lyophilised and should be kept at 2 to 8 °C sealed or at −20 °C for long-term storage, protected from light, and allowed to reach room temperature before opening. Both reconstitute in water or bacteriostatic water to a clear solution; add the solvent down the side of the vial and swirl rather than shake, because lipidated peptides foam and can aggregate under agitation. Both solutions keep at 2 to 8 °C for several weeks, and the conservative research practice is to use them within 28 days. Use low-binding tubes and PES or PVDF membranes where filtering is needed, since the diacid chain adsorbs to nylon and to ordinary polypropylene at low concentrations. The storage and stability guide and the reconstitution calculator cover the specifics.

What to look for on the certificate

A certificate for either compound should show RP-HPLC purity of 99 per cent or above with a single dominant peak, and an LC-MS identity line whose deconvoluted mass agrees with the expected value: about 4,113.6 Da for semaglutide, about 4,813.5 Da for tirzepatide. Because electrospray produces multiply charged ions, a certificate may instead quote a charge state; the certificate guide explains how to convert one to the other. Net peptide content matters for both, because the lyophilised powder carries bound water and trifluoroacetate counter-ions, so the mass of powder overstates the mass of peptide. For semaglutide in particular, watch for a late-eluting impurity at the main-peak mass plus 16 Da, which is the oxidised species; the molecule has no methionine, but tryptophan oxidation can occur on prolonged exposure to light.

Which to choose

For a receptor experiment, the question answers itself: semaglutide is the tool for GLP-1 receptor signalling in isolation, tirzepatide the tool for GIP/GLP-1 co-agonism and for the question of what the GIP receptor adds. For biased-signalling work, tirzepatide is the more interesting ligand at the GLP-1 receptor because of its documented bias, and semaglutide is the balanced comparator. For analytical or formulation work with a model lipidated peptide, semaglutide has the advantage of a slightly longer and better-characterised literature on degradation pathways and the larger body of published analytical methods.

The full accounts are in the monographs: semaglutide and tirzepatide. The triple agonist is compared with tirzepatide in tirzepatide vs GLP-3, and all four lipidated peptides in the family, including cagrilintide, are set out in semaglutide, tirzepatide, retatrutide and cagrilintide compared.

References

1. Lau J, Bloch P, Schäffer L, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. Journal of Medicinal Chemistry. 2015;58(18):7370–7380. doi:10.1021/acs.jmedchem.5b00726.
2. Coskun T, Sloop KW, Loghin C, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: From discovery to clinical proof of concept. Molecular Metabolism. 2018;18:3–14. doi:10.1016/j.molmet.2018.09.009.
3. Willard FS, Douros JD, Gabe MBN, et al. Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist. JCI Insight. 2020;5(17):e140532. doi:10.1172/jci.insight.140532.
4. Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. New England Journal of Medicine. 2021;385(6):503–515. doi:10.1056/NEJMoa2107519.
5. Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity. New England Journal of Medicine. 2025;393(1):26–36. doi:10.1056/NEJMoa2416394.
6. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183.
7. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. New England Journal of Medicine. 2023;389(24):2221–2232. doi:10.1056/NEJMoa2307563.

This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.