They are two different molecules, and in the one trial that compared them directly for obesity, tirzepatide produced more weight loss. Over 72 weeks, participants on tirzepatide lost an average of 20.2% of body weight against 13.7% on semaglutide (SURMOUNT-5, New England Journal of Medicine, 2025). That result is real, and it comes with conditions most summaries leave out - the trial was open-label, it was funded by tirzepatide’s manufacturer, and the semaglutide group was capped at 2.4 mg, below the 7.2 mg maximum Wegovy’s label now allows for adults. Which drug suits a particular person is a clinical decision, not a league table.
The mechanism, in plain language
Semaglutide is a GLP-1 receptor agonist. It imitates one gut hormone your body already releases after eating, the one that signals fullness, slows stomach emptying and prompts insulin release when blood sugar is high.
Tirzepatide acts on two receptors: GLP-1 and GIP. The FDA labels for both tirzepatide products describe it as a “glucose-dependent insulinotropic polypeptide (GIP) receptor and glucagon-like peptide-1 (GLP-1) receptor agonist” (Zepbound label). GIP is a second hormone in the same family, and adding it appears to change how the body handles both appetite and fat storage.
“Acts on two receptors instead of one” is a description of the drug, not a promise about your results. It is the honest reason to expect a difference, not a guarantee of one.
What the head-to-head trial actually found
SURMOUNT-5 randomly assigned 751 adults with obesity and without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg), injected once weekly for 72 weeks.
| Outcome at 72 weeks | Tirzepatide | Semaglutide |
|---|---|---|
| Mean weight change | -20.2% | -13.7% |
| Mean waist circumference change | -18.4 cm | -13.0 cm |
Participants on tirzepatide were also more likely to reach reductions of at least 10%, 15%, 20% and 25%. The difference on the primary endpoint was statistically significant.
Two qualifications belong with those numbers:
- It was open-label. Everyone knew which drug they were taking. Blinding matters most for outcomes involving effort and expectation, and weight is one of them.
- It was funded by Eli Lilly, which makes tirzepatide. Industry funding does not invalidate a trial, and this one was published in a major journal, but it is a fact a reader is entitled to have.
One trial in a population without diabetes, at those doses, over 72 weeks, is what we have. It is good evidence for the question it asked, and it is not the same as knowing how each drug performs for every person over years.
A separate point, and not a flaw in the trial above: semaglutide’s approved ceiling has since moved. Wegovy’s label now allows up to 7.2 mg weekly for adults who tolerate 2.4 mg and need further weight reduction, and SURMOUNT-5 capped the semaglutide arm at 2.4 mg. No head-to-head trial has compared tirzepatide against semaglutide at that higher dose, so how the comparison would look there is untested rather than settled.
The earlier head-to-head in type 2 diabetes, SURPASS-2, is a different trial answering a different question, and its dose asymmetry belongs to it alone: semaglutide was given at 1 mg while tirzepatide went to 15 mg. Tirzepatide lowered HbA1c more. Semaglutide’s approved maximum for that use is now higher than the dose it was tested against there.
Side effects
Both drugs produce mostly gastrointestinal effects, and in SURMOUNT-5 the most common adverse events in both groups were gastrointestinal, mostly mild to moderate, and concentrated during dose escalation.
Beyond that shared gastrointestinal core, the adverse-reaction lists belong to individual products rather than to the molecules, and the four products do not carry identical lists. Read the label for the product actually prescribed: Zepbound and Mounjaro for tirzepatide, Wegovy and Ozempic for semaglutide.
Both molecules carry a boxed warning about thyroid C-cell tumours seen in rodents, where the human relevance has not been determined. A personal or family history of medullary thyroid carcinoma, and multiple endocrine neoplasia syndrome type 2, are contraindications on these labels rather than points to raise for discussion. Hypersensitivity is also a contraindication, worded differently by product: Wegovy’s label says known hypersensitivity to semaglutide or its excipients, while Zepbound, Mounjaro and Ozempic each specify a serious hypersensitivity reaction. The current labels also warn about severe gastrointestinal adverse reactions, though each product’s label picked that section up on its own date.
Dosing
Both are once-weekly injections that start low and step up, specifically to reduce gastrointestinal effects.
- Tirzepatide starts at 2.5 mg weekly and increases in 2.5 mg steps after at least four weeks at a dose, to a maximum of 15 mg weekly in adults.
- Semaglutide for weight management starts at 0.25 mg weekly, titrating roughly every four weeks to a recommended maintenance dose of 2.4 mg weekly for adults. Wegovy’s label allows a further increase to a maximum of 7.2 mg weekly for adults who tolerate 2.4 mg for at least four weeks and for whom additional weight reduction is clinically indicated.
Semaglutide also exists in oral forms. We offer compounded semaglutide as once-daily drops as well as a weekly injection, compared at oral drops versus injections.
How the choice actually gets made
Weight-loss averages are one input among several. Tolerance often decides it in practice: the drug someone can stay on at an effective dose beats the one that looks better on paper and gets abandoned at week six. History matters too, including thyroid and pancreatic history, other medications, and whether type 2 diabetes is in the picture. Cost and supply are real constraints, not embarrassing ones.
At Gentle Health, compounded semaglutide starts at $112 a month for oral drops and $135 for the injection, and compounded tirzepatide starts at $169 a month, every dose tier published in advance. Full tables are at semaglutide cost and tirzepatide cost.
One distinction to keep straight throughout: compounded semaglutide and compounded tirzepatide are not FDA-approved, and they are not generic or equivalent versions of Wegovy, Ozempic, Zepbound or Mounjaro. The preparations we offer are made by state-licensed pharmacies for an individual patient under section 503A. The trial evidence above was generated with the approved products.
Frequently asked questions
Is tirzepatide simply better than semaglutide? In the one direct obesity trial, tirzepatide produced more weight loss over 72 weeks - open-label, manufacturer-funded, at the doses tested. It does not follow that it is the better choice for a given person, which depends on tolerance, history and what someone can sustain.
Can I switch from one to the other? That is a conversation with your prescriber rather than a decision to make alone, and it is an ordinary one. Both are titrated from a low starting dose when begun.
What do these cost compared with the brands? Compounded semaglutide starts at $112 a month here and compounded tirzepatide at $169, with every tier published. The wider spread across providers is explained at Why Do GLP-1 Prices Vary So Much?, and the full question library is at GLP-1 questions.
Dr. James Simmons, MD