Wegovy compared to other weight-loss treatments: what the evidence shows

The myth that these medicines are basically the same thing

A very common assumption (understandable, because both Wegovy and Mounjaro are weekly injections that work through gut-hormone pathways) is that the choice between them is mostly about price or brand preference. It isn't. The pharmacology is meaningfully different, and so are the average results in trials.

Wegovy works through a single receptor. Semaglutide mimics GLP-1, a hormone released after eating that signals fullness, slows gastric emptying, and acts on appetite centres in the brain. Tirzepatide, sold as Mounjaro in the UK, adds a second receptor to that picture: GIP. Activating both simultaneously appears to produce stronger appetite suppression in most people, which is reflected in the trial data.

That doesn't make Wegovy a lesser medicine. For plenty of people it is the right choice, and the evidence behind it is robust. The STEP 1 trial, published in the New England Journal of Medicine, followed 1,961 adults over 68 weeks and recorded an average body-weight reduction of around 15% on semaglutide 2.4mg. That is clinically significant by any measure. The point is simply that the two medicines are not interchangeable equivalents, they have different mechanisms and, on average, different results.

A quick check worth doing: if you're reading a comparison that doesn't mention SURMOUNT-5 at all, treat it with some scepticism. That 2025 head-to-head trial is the closest thing we have to a direct answer.

What SURMOUNT-5 actually found, and what the 7.2mg pen changes

SURMOUNT-5 was a 72-week open-label trial involving 751 adults with obesity and no diabetes, comparing tirzepatide directly against semaglutide 2.4mg. Published in the New England Journal of Medicine in 2025, it found that tirzepatide produced greater average weight reduction. NICE's appraisal of tirzepatide (TA1026) also noted that indirect comparisons favour tirzepatide over semaglutide.

That said, the picture shifted in early 2026. The MHRA approved a higher Wegovy maintenance dose of 7.2mg, first as multiple pens, then as a dedicated single-dose pen confirmed on 14 April 2026. Trials at 7.2mg reported average weight loss of around 20.7% over 72 weeks, which approaches tirzepatide 15mg territory. The 7.2mg pen is licensed for BMI 30 and above only, and reaching it requires the same gradual titration from 0.25mg under prescriber supervision.

So the gap between the two medicines is narrowing at their respective top doses. Whether you'd reach the highest dose of either (and how well you'd tolerate the journey) is something a prescriber is better placed to judge than any comparison article. If you want a sense of how semaglutide-based treatments line up against each other, that page covers the distinction between Ozempic and Wegovy specifically.

Eligibility, NICE guidance and the NHS route

Both medicines require a prescription following a clinical assessment. Neither is available over the counter.

NICE recommended tirzepatide for adults with a BMI of 35 or above plus at least one weight-related comorbidity (TA1026, December 2024). NICE recommended semaglutide (Wegovy) under TA875 for a maximum of two years, within a specialist weight management service. The NHS eligibility thresholds for both medicines are being phased in gradually; criteria differ in Scotland, Wales and Northern Ireland. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance in both cases.

For people who don't meet the NHS criteria or don't want to wait, private treatment through a regulated online pharmacy is the practical alternative. The weight-loss treatment overview on our site explains the licensed options clearly. If you're weighing up cost alongside clinical factors, our Wegovy cost page is the place to read about pricing context honestly, including what a legitimate prescription price should include and why market prices shifted in 2025.

Both medicines carry a Black Triangle (▼) in the UK, meaning the MHRA requires additional monitoring while post-marketing data builds. That applies equally to both.

Side effects and the practical differences between them

The side-effect profiles are broadly similar. Nausea, loose stools, constipation, indigestion and fatigue are common to both, most noticeable when starting or after a dose increase, and often settling within a couple of weeks. Injection-site reactions are possible with either.

There are some practical differences worth knowing. For tirzepatide specifically, women taking oral contraceptives need to add a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because GLP-1 medicines can reduce pill absorption. NHS guidance does not flag the same concern for semaglutide. That's a real clinical factor for some people.

The semaglutide overview on our site covers Wegovy's side-effect profile in more detail, and if you're curious about the manufacturer behind the medicine, our page on the Wegovy parent company sets out that background alongside the NHS medicines page for semaglutide, which remains a reliable first reference. If you want to look at how Wegovy lines up against Saxenda (liraglutide), that comparison is available separately.

Choosing between weight-loss medicines is a clinical decision. Our prescribers review each case individually, if you'd like to discuss which option suits your situation, the first step is a free consultation with the team.