Mounjaro or Wegovy for weight loss: the verdict

Mounjaro or Wegovy for weight loss is the choice thousands of people in the UK are weighing up right now. Both are once-weekly injections licensed for weight management, both quieten appetite by acting on gut hormones, and both are prescription-only. But they are different medicines with different average results and, dose for dose, different prices. Here is the honest head-to-head to help you and a prescriber land on the right one for you.

Mounjaro or Wegovy for weight loss: what's the difference?

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

Mounjaro is a brand of tirzepatide, a dual GIP and GLP-1 receptor agonist — sometimes called a "twincretin". It works on two gut-hormone pathways at once rather than one, and that dual action is thought to be why it tends to produce more weight loss. It is the newer of the two and, on the numbers, the more powerful.

Results: how much 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 15% over 68 weeks at the 2.4 mg maintenance dose, again versus roughly 2.4% on placebo. In the SURMOUNT-5 head-to-head study, tirzepatide averaged around 20% versus about 14% for semaglutide.

Trial numbers 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 dig deeper in our results comparison.

Tale of the tape

Price: what each costs privately

Wegovy is generally the cheaper starting point. Its cheapest tracked starter dose is £89 for four weeks, while Mounjaro's cheapest starter is £143.96. But the gap narrows once you look at treatment doses, and Mounjaro often delivers more weight loss per pound. Below are the ongoing (post-promo) starter prices at a spread of GPhC-registered and CQC-regulated providers, checked 01 September 2026.

Prices are set by each pharmacy and change often, so always confirm on the provider's own site before ordering. For the full league table across every dose, see the homepage price table and our detailed Mounjaro vs Wegovy price guide.

Our recommended provider, The Weight Clinic, offers both medicines with monthly video reviews and a refund if the prescriber declines you — a fair way to try either without gambling a full month's cost up front.

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. 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, and severe vomiting can dehydrate you and strain the kidneys. Whichever you take, report any suspected side effect through the MHRA Yellow Card scheme. Our side-effects comparison breaks each medicine down honestly.

Dosing: two different ladders

Both are titrated — started low and raised slowly — 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.

This matters if you ever want to change medicines. 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. Our guide on switching from Wegovy to Mounjaro explains what to expect.

So which should you choose?

If maximum average weight loss is your priority and the higher cost is sustainable, Mounjaro has the stronger evidence. If you want a cheaper entry point, a longer track record, or your prescriber flags a reason to favour semaglutide, Wegovy is a solid choice. Eligibility for both is typically a BMI of 30+, or 27+ with a weight-related condition — and a prescriber makes the final call after a consultation. For the complete picture, read our full UK comparison.

Frequently asked questions