Mounjaro®
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Start journey Learn moreThe factors that actually decide which medicine is right for you
What the trial data shows, and what it doesn't
The most direct evidence comes from SURMOUNT-5, a head-to-head trial published in the New England Journal of Medicine in 2025. Over 72 weeks, adults with obesity who received tirzepatide lost significantly more body weight on average than those on semaglutide 2.4 mg. That finding sits alongside the individual programme results: SURMOUNT-1 reported roughly 20–21% average weight loss at tirzepatide's 15 mg dose, while the STEP 1 trial found around 15% at semaglutide's 2.4 mg maintenance dose over 68 weeks.
Those numbers are worth taking seriously. They're also worth contextualising. Both trials enrolled thousands of adults who followed structured diet and activity programmes alongside the medicine, real-world results, without that structure, tend to vary. NICE's appraisal of tirzepatide (TA1026) acknowledges the indirect comparisons and SURMOUNT-5 findings when recommending tirzepatide, but it doesn't frame one medicine as universally superior. If you've been asking whether Wegovy is less effective than Mounjaro, the honest answer is that a 20% average is exactly that: an average. Some people respond very well to semaglutide and lose more than the trial mean; others plateau earlier on tirzepatide than the data would suggest.
There's also the newer Wegovy 7.2 mg dose to factor in. The MHRA approved a dedicated single-dose 7.2 mg pen in April 2026, with trial data reporting roughly 20.7% average weight loss over 72 weeks, closing the gap with tirzepatide's highest dose considerably, and those wondering whether Wegovy is as effective as Mounjaro at these higher doses will find the picture is still developing as real-world data accumulates. The fuller picture of how semaglutide compares to tirzepatide at these higher doses is still developing as real-world data accumulates.
How the two medicines differ in mechanism, and why that matters clinically
Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, which together reduce appetite, slow gastric emptying and influence blood-sugar regulation. Semaglutide works on the GLP-1 pathway alone. Whether a dual mechanism produces meaningfully better outcomes for a specific patient depends partly on their metabolic profile. For someone with type 2 diabetes, the GIP component in tirzepatide may offer additional glycaemic benefit. For someone whose main concern is weight without a diabetes diagnosis, the picture is less clear-cut.
Side effects follow a broadly similar GI-led pattern for both: nausea, vomiting, constipation, reflux and fatigue are the most commonly reported, usually most pronounced after starting or a dose increase and settling over days to a couple of weeks. The intensity and which specific symptoms dominate can differ between individuals, and some people find one medicine easier to tolerate than the other, regardless of which produces greater weight loss on paper. Tolerability is a legitimate clinical factor, not a consolation prize for choosing the 'lesser' option, and it's one reason why concluding that Wegovy is simply not as effective as Mounjaro overlooks how much individual response varies.
Explore the full Wegovy vs Mounjaro breakdown for a more detailed look at how the two medicines compare across mechanism, dosing schedule and licensed uses.
Eligibility, prescription and NHS access: not the same for both
Both medicines are licensed for weight management in adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. However, the NHS commissioning criteria differ.
NICE recommends tirzepatide (TA1026) for adults with a BMI of 35 or above plus at least one weight-related comorbidity, through a phased NHS rollout that is now expanding. NICE's recommendation for semaglutide (TA875) requires use within a specialist weight management service for a maximum of two years, with slightly different eligibility parameters. On the NHS, cost and access routes also differ in practice, and waiting lists for NHS treatment remain long in most areas.
Privately, both are available following clinical assessment, and the prescriber's job is to match the medicine to the patient, not to default to whichever scored higher in a trial. A useful starting point is our treatment overview, which explains the options clearly alongside the consultation process.
The comparison at a glance
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide injection) |
|---|---|---|
| Mechanism | Dual GIP + GLP-1 receptor agonist | GLP-1 receptor agonist |
| Average weight loss (highest licensed dose, clinical trials) | ~20–21% at 15 mg (SURMOUNT-1, 72 weeks) | ~15% at 2.4 mg (STEP 1, 68 weeks); ~20.7% at 7.2 mg (72 weeks) |
| Head-to-head result | Greater average loss (SURMOUNT-5, NEJM 2025) | Lower average loss than tirzepatide at 2.4 mg in SURMOUNT-5 |
| UK weight-loss licence | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30, or ≥27 with a weight-related condition |
| NICE NHS recommendation | TA1026 (phased rollout, BMI ≥35 + comorbidity | TA875) specialist service, max 2 years, BMI ≥35 + comorbidity |
| Side-effect profile | GI-led; broadly similar to semaglutide | GI-led; broadly similar to tirzepatide |
Sources: NICE TA1026 (tirzepatide); NICE TA875 (semaglutide); SURMOUNT-5, NEJM 2025. Numbers are trial averages and hedge accordingly in practice.
Which of the two fits your health profile is a clinical decision our prescribers make with you, not something a comparison table can resolve. If you'd like that conversation, check your eligibility with a free consultation.
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