Mounjaro vs Wegovy: the full UK comparison (2026)

Mounjaro vs Wegovy is the only question this site exists to answer. Both are once-weekly injections licensed in the UK for weight management, both work by quietening appetite, and both are prescription-only. But they are not the same medicine, they do not produce the same average results, and — dose for dose — they rarely cost the same. This is the full head-to-head: results, side effects, dosing, NHS access and real private prices, refereed without favourites.

What each medicine actually is

Wegovy is a brand of semaglutide, a GLP-1 receptor agonist. It mimics one natural gut hormone to reduce appetite and "food noise", help you feel full sooner, and slow how quickly the stomach empties. It is the more established of the two and has the longer track record in weight management.

Mounjaro is a brand of tirzepatide, a dual GIP and GLP-1 receptor agonist — a "twincretin". It targets two gut hormones at once rather than one. That dual action is thought to be why it tends to produce more weight loss than GLP-1-only drugs. It is the newest of the current UK options and, on the numbers, the most powerful.

Results: how much weight comes off

This is where the two separate most clearly. In the SURMOUNT-1 trial, adults with obesity or overweight (without type 2 diabetes) lost a mean of 16.0% of body weight at 5 mg, 21.4% at 10 mg and 22.5% at 15 mg of Mounjaro over 72 weeks, against 2.4% on placebo. About 90% of people on 15 mg lost at least a tenth of their body weight.

For Wegovy, the landmark STEP 1 trial showed a mean loss of about 14.9% — roughly 15% — of body weight over 68 weeks at the 2.4 mg maintenance dose, again versus around 2.4% on placebo. In head-to-head research, tirzepatide has out-performed semaglutide on average weight loss.

Numbers from trials are averages, not promises. Real-world results depend on the dose you reach, how well you tolerate it, and the diet and activity changes alongside. We go deeper in our results comparison.

Tale of the tape

Side effects: broadly similar

The side-effect profiles overlap heavily. Both most commonly cause gut symptoms — nausea, diarrhoea, constipation and vomiting — which usually ease as the body adjusts and doses climb slowly. Nausea is reported by roughly 40% of Wegovy users at some point. Both start low and titrate up precisely to keep these manageable.

Rare but serious risks are also similar: pancreatitis (rare) and gallstones apply to both. Wegovy carries a specific rare eye-condition signal (NAION); Mounjaro can strain the kidneys through dehydration if vomiting is severe. Whichever you take, report any suspected side effect through the MHRA Yellow Card scheme. Our side-effects comparison breaks each down.

Dosing: two different ladders

Both medicines are titrated — started low and raised slowly to reduce side effects — but the ladders differ. Mounjaro begins at 2.5 mg weekly for four weeks (a starter dose, not a treatment dose), then steps up through 5, 7.5, 10, 12.5 to a maximum of 15 mg, with at least four weeks between increases. Wegovy climbs 0.25 → 0.5 → 1 → 1.7 → 2.4 mg, its maintenance dose.

This matters for switching. Moving from Wegovy to Mounjaro is not a like-for-like swap: you restart on Mounjaro's 2.5 mg starter and titrate up again. See our guide on switching from Wegovy to Mounjaro for what to expect.

NHS access in 2026

Both are NHS-approved but access is tight. Mounjaro is recommended by NICE (TA1026, Dec 2024) and being rolled out in phases from 2025, prioritising the highest BMI and most weight-related conditions first, so availability still varies by area. Wegovy is available on the NHS only through specialist weight-management services (NICE TA875) for up to two years. Both are available far more widely on private prescription for adults with a BMI of 30+ (or 27+ with a weight-related condition).

Price: what you'll pay privately

Across the 24 regulated UK pharmacies we track, Wegovy tends to be a little cheaper dose-for-dose, though it's close and varies by pharmacy. The table below shows our recommended provider's headline prices alongside the market range we've recorded. Prices were last checked 4 July 2026 and can change — always confirm on the pharmacy's own site.

Providers are GPhC/CQC-regulated. This is price information, not an offer of supply. Confirm the current price on the provider's own site. See the full 24-pharmacy tables on our homepage and the deep-dive in our price comparison.

So which should you choose?

If maximum average weight loss is the priority and your prescriber agrees, Mounjaro has the stronger trial numbers. If you want the longer-established medicine, often at a slightly lower dose-for-dose price, Wegovy is a sound, well-evidenced choice. For many people the deciding factors are tolerability, cost you can sustain over months, and clinical suitability — none of which a website can settle for you. Take this comparison to a prescriber and let them make the call.

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