What is the difference between Ozempic and Mounjaro?
Semaglutide copies a gut hormone, GLP-1, and shares about 94% of its sequence with the human version. Tirzepatide is a single molecule that acts on GLP-1 receptors and on GIP receptors, a second gut hormone pathway. Both are injected weekly, because the half-life is about a week for semaglutide and about 5 days for tirzepatide. Both slow the emptying of the stomach, and tirzepatide's package insert describes lower appetite, greater fullness and fewer cravings, with most of the weight lost being fat.
The brands matter for this question. Ozempic (semaglutide) is registered in Malaysia for type 2 diabetes, at doses up to 1 mg weekly. Semaglutide for weight management is Wegovy (semaglutide), stepped up to 2.4 mg. Mounjaro (tirzepatide) is registered for both type 2 diabetes and weight management in adults, with a BMI of 30 or more, or 27 to under 30 with at least one weight-related condition. So when a weight trial is described as "Ozempic vs Mounjaro", the semaglutide in it is at the weight-management dose. SURMOUNT-5 used 1.7 or 2.4 mg. A trial at the Ozempic dose is SURPASS-2, in adults with type 2 diabetes, which used semaglutide 1 mg.
What did the head-to-head trials find?
SURMOUNT-5 was an open-label phase 3b trial of 751 adults with obesity, or overweight plus a weight-related condition, and no diabetes, in the United States and Puerto Rico, over 72 weeks. People took the maximum tolerated dose: tirzepatide 10 or 15 mg, or semaglutide 1.7 or 2.4 mg. Average weight loss was 20.2% (95% CI 19.1 to 21.4) on tirzepatide and 13.7% (12.6 to 14.9) on semaglutide. On average, waist circumference fell by 18.4 cm and 13.0 cm, and weight by 22.8 kg and 15.0 kg.
The sponsor's summary of the trial data gives the share of people reaching each threshold, tirzepatide against semaglutide: 10% or more lost, 81.6% and 60.5%; 15%, 64.6% and 40.1%; 20%, 48.4% and 27.3%; 25%, 31.6% and 16.1%.
SURPASS-2 was open-label too: 1,879 adults with type 2 diabetes, 40 weeks, tirzepatide 5, 10 or 15 mg against semaglutide 1 mg. Its main measure was blood sugar, which is outside this article. On weight, the tirzepatide groups lost an average of 1.9, 3.6 and 5.5 kg more than the semaglutide group.
What did not differ?
In SURMOUNT-5, stomach events were common in both arms, mostly mild to moderate, and mostly during the dose steps. Stopping because of side effects happened in 6.1% on tirzepatide and 8.0% on semaglutide, and for stomach events in 2.7% and 5.6%. The sponsor's summary states that the study was "not powered to compare the safety and tolerability", so those percentages describe the trial and settle nothing about which is easier to take.
In SURPASS-2, nausea occurred in 17 to 22% on tirzepatide and 18% on semaglutide, diarrhoea in 13 to 16% and 12%, and vomiting in 6 to 10% and 8%. Serious adverse events were 5 to 7% and 3%.
Both medicines take some lean mass with the fat. In the SURMOUNT-1 body composition substudy of 160 adults, about three quarters of the weight lost on tirzepatide was fat and a quarter was lean mass, on average, which was the same split as on placebo. Lean mass is not the same as muscle. A small pooled analysis of three trials of two other GLP-1 medicines, liraglutide and dulaglutide, in 171 adults with obesity and without type 2 diabetes, found on average 0.78 kg more lean mass lost than in the control groups.
What are the limits of that result?
SURMOUNT-5 was open-label, so participants and staff knew which medicine was being taken. It was funded by tirzepatide's maker. It enrolled people in the United States and Puerto Rico only, none with diabetes, and it ran for 72 weeks. The doses were the maximum each person tolerated, not a fixed dose. Above all it reports an average. Inside every average, some people lost far more and some far less.
Heart and kidney trials are a separate body of evidence for each medicine, outside this article. As of 30 September 2026, no randomised trial has compared semaglutide and tirzepatide on those outcomes.
Why does the choice depend on the person?
The choice between them depends on the medical picture, the goals, and what suits the individual patient. Several practical points sit inside that. The registered use in Malaysia comes first, since Ozempic and Mounjaro are not registered for the same things. Existing heart, kidney or diabetes conditions also matter, and decisions about their treatment sit with the person's own physician.
Then tolerance. Both medicines are stepped up slowly for that reason, and the guideline says to stop if significant safety or tolerability problems appear. Pregnancy timing differs: semaglutide is stopped at least 2 months before a planned pregnancy, tirzepatide at least 1 month before, with contraception advised for women who could become pregnant on tirzepatide. Tirzepatide also has a note on the contraceptive pill: the US label advises a non-oral or added barrier method for 4 weeks after starting and after each dose step, while the Malaysian insert reports a fall in ethinyl estradiol after a single 5 mg dose that it does not consider clinically relevant. That belongs in the assessment.
Eye disease is another factor. In people with type 2 diabetes who already had retinopathy, semaglutide at 0.5 to 1 mg weekly was followed by an early, temporary worsening of the retinopathy, and the Malaysian guideline advises close monitoring and co-management with an ophthalmologist. A larger or faster loss can also change the face, which is covered in hollow eyes after fast weight loss.
The Malaysian obesity guideline says to choose a medicine on efficacy, side effects and cost, and only alongside diet, exercise and behaviour change. What is checked before any of these is prescribed is set out in what a doctor checks before prescribing GLP-1 medication, and what a medical weight assessment decides describes the evaluation. The side effects of both, with trial figures, are in weight-loss injection side effects: what to expect.
What happens after either medicine stops?
The same question follows both. The STEP 1 extension followed 327 people for a year after treatment stopped. Those who had taken semaglutide 2.4 mg had lost an average of 17.3% of body weight by week 68, and by week 120 they had regained an average of 11.6 percentage points of it. That extension studied semaglutide. The guideline treats obesity as chronic, notes that courses of 6 months or less do not sustain the loss, and says weight returns after stopping. Rebound weight after stopping GLP-1 sets out the wider evidence.
A difference in average loss over 72 weeks answers one question. Which medicine, at which dose, and for how long is decided at an evaluation, and it can change at any review.
