What the research shows
Semaglutide vs tirzepatide: what the head-to-head trial found
Sources verified against the primary documents on 9 July 2026.
The short answer
They have been compared directly. In SURMOUNT-5, a 72-week randomised trial in 751 adults with obesity and without diabetes, tirzepatide produced a mean weight reduction of 20.2% against 13.7% for semaglutide. Tirzepatide activates two receptors (GIP and GLP-1); semaglutide activates one. The trial was open-label and funded by tirzepatide’s manufacturer, and “more weight loss” is not the same as “better for you”.
Key facts
- Trial
- SURMOUNT-5, 72 weeks, 751 participants
- Tirzepatide
- −20.2% body weight
- Semaglutide
- −13.7% body weight
- Waist circumference
- −18.4 cm vs −13.0 cm
What SURMOUNT-5 actually did
Most comparisons of these two drugs are indirect — putting the results of separate trials, with different populations, side by side. SURMOUNT-5 is not that. It randomised 751 adults with obesity and without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or the maximum tolerated dose of semaglutide (1.7 or 2.4 mg), once weekly for 72 weeks.
At week 72 the least-squares mean weight change was −20.2% with tirzepatide and −13.7% with semaglutide. Waist circumference fell 18.4 cm versus 13.0 cm. Both differences were statistically significant.
This is about as clean an answer to "which one causes more weight loss" as this field produces.
Three caveats that belong with the number
First, the trial was open-label. Participants and investigators knew which drug was being given. For a subjective or effort-dependent outcome that would be fatal; for body weight measured on a scale it matters less, though expectations influence behaviour.
Second, it was funded and run by Eli Lilly, which manufactures tirzepatide. That does not make the result wrong — industry funds most obesity trials, and the design was randomised and pre-registered — but it is a fact a reader is entitled to weigh.
Third, and most often missed: the doses are not symmetric in the way they look. Tirzepatide’s maximum approved dose for obesity is 15 mg; semaglutide’s is 2.4 mg. The trial compared each drug at its own ceiling. That is the clinically relevant question, and it is not the same as comparing them at equivalent receptor occupancy.
Why one outperforms the other
Semaglutide is a GLP-1 receptor agonist. Tirzepatide is a dual agonist: it activates both the GIP and the GLP-1 receptor in a single molecule. Whether GIP agonism ought to help was contested for years — there were respectable arguments for blocking it instead. Tirzepatide works, which settled the practical question well ahead of the mechanistic one.
The next step in this logic is retatrutide, which adds glucagon receptor agonism to increase energy expenditure. Its phase 2 results are striking. It is not an approved drug, and phase 2 results have disappointed before.
“More weight loss” is not the whole question
Tolerability, cost, insurance coverage, cardiovascular outcome data, and whether you can stay on the drug all bear on which is better for a given person. Semaglutide has the longer cardiovascular outcomes record. This is a decision for a clinician, not a table.
Compounds referenced in this guide
Semaglutide is used or studied for weight loss; glycemic control and related fat loss and metabolic health goals. Potential benefits and safety depend on indication, formulation, dose, and medical supervision.
Tirzepatide is used or studied for significant weight loss; glucose control and related fat loss and metabolic health goals. Potential benefits and safety depend on indication, formulation, dose, and medical supervision.
Retatrutide is used or studied for extreme weight loss (trials) and related fat loss and metabolic health goals. Potential benefits and safety depend on indication, formulation, dose, and medical supervision.
Frequently asked questions
Is tirzepatide better than semaglutide?
For weight reduction over 72 weeks, the head-to-head SURMOUNT-5 trial found tirzepatide produced more: 20.2% versus 13.7%. “Better” depends on more than that — tolerability, cost, access, cardiovascular outcome evidence, and whether a person can remain on the drug all matter, and the trial was open-label and industry-funded.
What is the difference between semaglutide and tirzepatide?
Semaglutide activates the GLP-1 receptor. Tirzepatide is a single molecule that activates both the GIP receptor and the GLP-1 receptor. Because the ratio of activity at each receptor is fixed by the molecule’s chemistry, it cannot be adjusted by changing the dose.
Are Ozempic and Wegovy the same as Mounjaro and Zepbound?
Ozempic and Wegovy are both semaglutide, approved for different indications at different maximum doses. Mounjaro and Zepbound are both tirzepatide, likewise. The brand name reflects the approved indication, not a different molecule. Check any product against Drugs@FDA and read its label on DailyMed.
Was the head-to-head trial blinded?
No. SURMOUNT-5 was an open-label, phase 3b randomized controlled trial. Participants and investigators knew which drug was administered. Randomisation was preserved, and the primary outcome — percent change in body weight — is objectively measured, which limits though does not eliminate the concern.
Sources
Every link below was checked and resolved before publication. Where a claim could not be traced to a primary document, we left it out.
- Aronne LJ, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022
- Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023
- Drugs@FDA — check whether a drug is FDA-approved
- DailyMed — official FDA drug labelling (U.S. National Library of Medicine)
Written by Pepperz Editorial and not medically reviewed — see our editorial standards. Educational reference only. Pepperz does not provide medical advice, diagnosis, treatment, prescribing guidance, or dosing recommendations.