The short version
Semaglutide is a 31-residue human-GLP-1 analogue that activates one receptor. Tirzepatide is a 39-residue GIP-based peptide that activates two, GIP and GLP-1. In SURMOUNT-5 — the one direct comparison, published in 2025 — tirzepatide 15 mg produced −20.2% body weight at 72 weeks versus −13.7% with semaglutide 2.4 mg. Semaglutide's counterweights are the deepest outcomes evidence in the class (cardiovascular, kidney, heart failure), an oral formulation, and the longest safety record.
Two different starting points
Semaglutide starts from human GLP-1(7-37) and keeps 29 of 31 residues, adding Aib at position 8, Arg at 34 and a C18 fatty diacid on Lys26. Tirzepatide starts from the other incretin, GIP: its N-terminal core is GIP-derived (hence the tyrosine at position 1 rather than GLP-1's histidine), its C-terminal tail is borrowed from exendin-4, and it carries Aib at positions 2 and 13 and a C20 fatty diacid on Lys20. They are not variations on one molecule; they are two different hormones re-engineered with the same toolkit.
| Feature | Semaglutide | Tirzepatide |
|---|---|---|
| Parent hormone | GLP-1 (human) | GIP (human) + exendin-4 tail |
| Length | 31 aa | 39 aa |
| Non-canonical residues | Aib8 | Aib2, Aib13 |
| Acylation | Lys26 · C18 diacid-γGlu-2×OEG | Lys20 · C20 diacid-γGlu-2×OEG |
| C-terminus | Free acid | Amide |
| Formula / mass | C187H291N45O59 / ≈ 4,114 Da | C225H348N48O68 / ≈ 4,814 Da |
| Receptors | GLP-1R | GIPR + GLP-1R |
| Half-life | ≈ 7 days | ≈ 5 days |
Receptor pharmacology
Semaglutide is a full GLP-1 receptor agonist with an affinity of about 0.38 nM. Tirzepatide binds the GIP receptor about as well as native GIP but the GLP-1 receptor several-fold more weakly than native GLP-1, with signalling biased toward cAMP over β-arrestin. That imbalance is deliberate: GIP receptor activity in adipose tissue and the brain adds weight loss and appears to blunt nausea, while the biased, weaker GLP-1 receptor engagement reduces receptor desensitisation. Whether the extra efficacy comes mainly from GIP agonism or from the biased GLP-1 signalling is still debated in the literature.
Half-life and dosing
Semaglutide's half-life is about 7 days (145–165 hours); tirzepatide's about 5 days (≈117 hours). Both are once-weekly injections with stepwise escalation. Semaglutide for weight management escalates over 16 weeks to 2.4 mg; tirzepatide starts at 2.5 mg and rises in 2.5 mg steps to a maximum of 15 mg. Semaglutide is also available as a daily tablet (Rybelsus), which no other peptide in the class matches, though the non-peptide orforglipron now competes in that space.
SURMOUNT-5: the head-to-head
SURMOUNT-5 (Aronne et al., NEJM 2025) randomised 751 adults with obesity but without diabetes to maximum tolerated doses of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks. Weight change was −20.2% with tirzepatide versus −13.7% with semaglutide; waist circumference fell 18.4 cm versus 13.0 cm; and more tirzepatide participants reached every threshold from 10% to 25% loss. Adverse events were gastrointestinal in both arms, mostly mild to moderate, and concentrated during escalation. In type 2 diabetes, SURPASS-2 had earlier shown greater HbA1c and weight reduction with tirzepatide than with semaglutide 1 mg over 40 weeks.
| Endpoint | Tirzepatide | Semaglutide 2.4 mg |
|---|---|---|
| Mean weight change | −20.2% | −13.7% |
| Waist circumference | −18.4 cm | −13.0 cm |
| Participants | 751 total | — |
Where semaglutide's evidence is deeper
Efficacy on the scale is one endpoint. Semaglutide has completed outcome trials that tirzepatide has not: SELECT (20% relative reduction in cardiovascular events in obesity without diabetes), FLOW (24% reduction in kidney-disease progression in type 2 diabetes), STEP-HFpEF (heart failure symptoms), and SUSTAIN-6 (cardiovascular events in diabetes). Tirzepatide's SURPASS-CVOT reported in 2025 against dulaglutide, and SUMMIT showed benefit in heart failure with preserved ejection fraction, but its cardiovascular database is younger. For readers weighing the two, this is the dimension that cross-trial weight percentages do not capture.
Reading the comparison responsibly
Both are approved prescription medicines, manufactured under pharmaceutical GMP, with labels, safety databases and quality systems. Products sold online as “research” semaglutide or tirzepatide are outside all of that, and regulators in the US, Canada and the EU have issued repeated warnings about counterfeit and mis-dosed material. This guide compares molecules and evidence; it is not a recommendation of either drug, and choosing between them is a prescriber's decision.
Sources and what they cover
These primary studies, official records and standards cover the topics linked below. The scope notes distinguish laboratory findings, human trials and regulatory records. This is a selected bibliography, not a systematic review or verification of every sentence; absence of a study here does not prove that no study exists.
- Willard et al. (2020) — Tirzepatide as an imbalanced, biased dual receptor agonist
Primary receptor pharmacology and molecular design; not itself a clinical outcomes trial.
Relevant sections: Two different starting points · Receptor pharmacology
- Aronne et al. (2025) — SURMOUNT-5: tirzepatide compared with semaglutide
Direct randomized comparison in adults with obesity without diabetes; does not rank all uses of the two medicines.
Relevant sections: SURMOUNT-5: the head-to-head · Reading the comparison responsibly
- Lincoff et al. (2023) — Semaglutide and cardiovascular outcomes in obesity
SELECT trial in adults with established cardiovascular disease; outcome evidence is specific to that population.
Relevant sections: Where semaglutide's evidence is deeper
FAQ
What is the core difference between semaglutide and tirzepatide?+
Semaglutide is a GLP-1 analogue acting on one receptor. Tirzepatide is a GIP-based peptide acting on both the GIP and GLP-1 receptors. In the SURMOUNT-5 head-to-head, tirzepatide produced about 6.5 percentage points more weight loss at 72 weeks.
Are both approved medicines?+
Yes. Semaglutide is sold as Ozempic, Wegovy and Rybelsus; tirzepatide as Mounjaro and Zepbound. Both are approved in the US, Canada and the EU.
Which has the longer half-life?+
Semaglutide, at about 7 days versus tirzepatide's 5. Both are dosed once weekly.
Which one is better?+
SURMOUNT-5 showed greater weight loss with tirzepatide. Semaglutide has more outcomes evidence (cardiovascular, kidney, heart failure) and an oral form. Which matters more depends on the person and is a clinical decision.
Is tirzepatide a GLP-1 like semaglutide?+
It activates the GLP-1 receptor, but its sequence is GIP-based and it activates the GIP receptor at least as strongly. The accurate label is dual GIP/GLP-1 receptor agonist.