Semaglutide is the molecule sold as Wegovy for weight management and Ozempic for type 2 diabetes, with Rybelsus as the tablet form; tirzepatide is sold as Mounjaro and, in the United States, as Zepbound. Those are the registered product names. The comparison below is between the two molecules, because that is what the trial compared and what a prescription in Singapore is written against.

In the one trial that compared them directly, tirzepatide produced more weight loss than semaglutide: −20.2% against −13.7% over 72 weeks. That is a clear result and it is not the whole picture, because a 2026 analysis of 262 trials found that tirzepatide also removed more lean mass than any other drug studied. This article sets out the head-to-head, why the two medicines' separate trials cannot be lined up against each other, what each is registered for in Singapore, and the variable that decides more than the molecule does.

Availability in Singapore. This medicine is registered with Singapore's Health Sciences Authority, and its registered indication includes weight management. Which medicine suits a particular person, if any does, is decided by the doctor who assesses them — we do not promote a named product.

Both molecules are registered here for weight management, under different brands: semaglutide at 2.4 mg, and tirzepatide on its current registrations.

Is Mounjaro more effective than Wegovy? What SURMOUNT-5 found

SURMOUNT-5 randomised 751 adults with obesity but without type 2 diabetes to the maximum tolerated dose of tirzepatide (10 mg or 15 mg) or the maximum tolerated dose of semaglutide (1.7 mg or 2.4 mg), once weekly, for 72 weeks.

Least-squares mean weight change at week 72 was −20.2% with tirzepatide and −13.7% with semaglutide (Wegovy). Mean waist circumference change was −18.4 cm against −13.0 cm. Participants on tirzepatide were more likely to reach reductions of at least 10%, 15%, 20% and 25% (Aronne 2025).

The trial was open-label. Participants and investigators knew which medicine was which, which is a real limitation on a trial whose outcome depends partly on behaviour, and it is stated in the paper rather than hidden in it. The most common adverse events in both groups were gastrointestinal, mostly mild to moderate, and mostly during dose escalation.

Individual results vary and are not guaranteed.

Why their separate trials cannot be compared

This is the commonest error in writing about these two medicines, and it is worth naming.

STEP 1 enrolled 1,961 adults over 68 weeks and reported mean weight change of −14.9% against placebo, using a primary estimand that assessed effects regardless of treatment discontinuation or rescue intervention (Wilding 2021).

SURMOUNT-1 enrolled 2,539 adults over 72 weeks and reported up to −20.9% at the 15 mg dose, using a treatment-regimen estimand in the intention-to-treat population (Jastreboff 2022).

Different people, different durations, different statistical definitions of what "the effect" means. Setting −14.9% beside −20.9% and calling the gap a comparison treats two different measurements as one number. The head-to-head trial exists because that comparison could not otherwise be made.

What the difference in design is

Semaglutide acts at the GLP-1 receptor. Tirzepatide acts at the GLP-1 receptor and at the GIP receptor as well.

Both are gut hormones released when you eat, and both feed into the systems governing appetite and blood sugar. Acting at two rather than one is the design difference, and the likeliest explanation for the difference in the trials. The class mechanism is covered in how GLP-1 medications work.

What each is registered for here

The licences are not the same, and the difference is not decorative.

Semaglutide 2.4 mg carries a weight-management indication and, separately, an indication to reduce the risk of major adverse cardiovascular events in adults with established cardiovascular disease and either obesity or overweight (NDF).

Tirzepatide, on its current registrations, carries a type 2 diabetes indication and a weight-management indication. It carries no cardiovascular risk-reduction indication here (NDF).

For someone who has both obesity and established cardiovascular disease, that is a difference a doctor would weigh.

The measurement nobody puts in the headline

A 2026 network meta-analysis pooled 262 trials and 99,791 participants across 19 drugs and looked at composition, not only weight.

Tirzepatide reduced fat mass the most, by 25.7% — and reduced lean mass the most, by 8.3%. Subcutaneous semaglutide was the only drug in the analysis associated with reduced all-cause mortality, at a risk ratio of 0.81, an estimate largely informed by cardiovascular outcome trials in high-risk populations. Both agents reduced heart failure risk (Nong 2026). Those are pooled trial averages, and individual results vary.

Read that carefully, because it does not say what a headline would make of it. More total loss with more lean loss is not automatically a worse outcome — someone losing a fifth of their body weight has lost a great deal of fat. What it does mean is that the plan around the most effective medicine matters more than the plan around a weaker one, not less. The protein, the resistance training and the rate of loss are doing more work, against a bigger gradient.

That is the whole argument of this clinic, and here it is in someone else's meta-analysis. We cover what the evidence shows about lean tissue in how much muscle you lose on GLP-1 medication, and the training side in the minimum effective resistance training.

The things that are not the molecule

A trial average describes a population over a fixed period. It says nothing about one person.

What a doctor weighs instead: what someone tolerates, what their history and other medicines allow, which registered indication actually fits them, and — the one that decides most outcomes — what they can stay on. A medicine that produces less on paper and is still being taken in a year has outperformed one that was stopped in month three.

Which of these, if either, is appropriate for you is a clinical decision made after an assessment. Being offered something other than the largest number in a headline is not a verdict on you.

At GetLean, our philosophy is that the medication is the catalyst and what you keep is the result.

Common questions

Is Mounjaro better than semaglutide for weight loss?

Tirzepatide, in the one trial that compared them directly. SURMOUNT-5 randomised 751 adults with obesity and without type 2 diabetes and found least-squares mean weight change at week 72 of −20.2% against −13.7% (Aronne 2025). It was open-label. Individual results vary and are not guaranteed.

Can I compare the figures from their separate trials?

Not reliably. STEP 1 and SURMOUNT-1 ran different populations, over different durations, using different statistical estimands (Wilding 2021, Jastreboff 2022). Lining up −14.9% against −20.9% treats two different measurements as though they were one. The head-to-head exists precisely because that comparison could not be made.

Does the bigger number mean a better outcome?

Not on its own. A 2026 network meta-analysis of 262 trials found tirzepatide reduced fat mass the most, by 25.7%, and reduced lean mass the most as well, by 8.3% (Nong 2026). More total loss with more lean loss is a reason the plan around the medicine matters more, not less.

Are they registered for the same things in Singapore?

No. Semaglutide 2.4 mg carries a weight-management indication and a separate cardiovascular risk-reduction indication (NDF). Tirzepatide's current registrations carry type 2 diabetes and weight management, and no cardiovascular indication (NDF). The licences differ, and that is a real input to a clinical decision.

Should I ask for the stronger one?

Which medicine is appropriate is a clinical judgement made after an assessment, and it turns on tolerance, medical history, the registered indications and what a person can stay on — not on a trial average. Being offered something other than the largest number in a headline is not a verdict on anyone.