Wegovy or Mounjaro — which is better for weight loss?

Step 1: Understand what each medicine actually does

Wegovy contains semaglutide, a GLP-1 receptor agonist. It mimics a hormone your gut releases after eating, slowing how quickly your stomach empties and signalling to your brain that you're full. It's given as a once-weekly subcutaneous injection, starting low and building up over several months.

Mounjaro contains tirzepatide and goes one step further. It activates both the GLP-1 receptor and the GIP receptor, two distinct gut-hormone pathways involved in appetite regulation and blood-sugar control. Because it works on both at once, it is classed as a dual agonist, the only one licensed for weight management in the UK. You can read more about how semaglutide and tirzepatide differ if you want the full mechanistic picture. The practical upshot is that the two medicines are similar in their side-effect profile but meaningfully different in the results the clinical trials reported.

Both work best alongside a reduced-calorie diet and more physical activity. Neither is a standalone fix. The NHS patient information pages for tirzepatide and semaglutide cover the basics clearly and are worth reading early.

Step 2: Look at the trial evidence, including the direct comparison

For most of the time these medicines existed, comparisons relied on separate trials run in different populations at different times. That changed with SURMOUNT-5, a 72-week open-label trial that placed tirzepatide and semaglutide 2.4mg head-to-head in 751 adults with obesity and no diabetes. Tirzepatide produced greater average weight reduction. NICE referenced indirect comparisons that favour tirzepatide in its appraisal of the medicine, published as NICE technology appraisal TA1026.

For Mounjaro specifically, SURMOUNT-1 (2,539 participants, 72 weeks) recorded average body-weight reductions of around 20–21% at the 15mg maintenance dose. Wegovy's pivotal STEP 1 trial reported around 15% average reduction at 2.4mg over 68 weeks.

The gap is real, but it has narrowed. The MHRA approved a 7.2mg dose of Wegovy in January 2026, and a dedicated single-dose pen for that strength followed in April 2026. Trials reported roughly 20.7% average weight loss at 7.2mg over 72 weeks. So if you've read that Mounjaro is clearly better, that comparison is becoming more nuanced at the top dose ranges. If you want the fuller picture on whether Wegovy is the right choice for your situation, that page covers it in more depth.

Step 3: Consider the practical and eligibility differences

You may be surprised to learn that suitability often comes down to factors that have nothing to do with which medicine loses more weight on average. A few things to think about.

If you take the oral contraceptive pill, the guidance differs: for tirzepatide, women are advised to use an additional non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, because absorption of the pill can be reduced. The NHS does not flag the same requirement for semaglutide. Similarly, NHS England suggests considering transdermal HRT (patches or gels) while on tirzepatide for the same absorption reason. These are worth raising with a prescriber before you choose. You might also find the section on managing side effects on Wegovy useful if nausea is a concern, the GI profile is similar for both medicines.

On the cost side, prices have moved. Eli Lilly raised Mounjaro's UK list price from 1 September 2025, and typical private monthly costs now vary across providers and doses. For a clearer look at what you might actually pay, the Wegovy cost page gives a straightforward breakdown of how private treatment is structured. Neither medicine is cheap, which makes it worth understanding exactly what a provider's price includes, prescription, aftercare and delivery all vary.

Under UK licensing rules, both medicines are for adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related condition. Lower thresholds apply for some ethnic backgrounds under UK guidance. A prescriber looks at the whole clinical picture, not just the BMI figure, before recommending either option.

Step 4: Recognise what the data cannot tell you

We hear this question a lot, and honestly, the frustration behind it is completely understandable. Spending time reading conflicting claims online, or finding that your GP's waiting list stretches months ahead, makes you want a clear answer before you commit to anything.

The data gives population averages. Your response to either medicine will depend on how your body tolerates the titration, which dose you reach, how consistently you manage the lifestyle changes alongside it, and factors your prescriber will look for that trials can only partly capture. Some people do significantly better on tirzepatide. Some find semaglutide suits them perfectly. A small number do better moving from one to the other.

That's why the choice isn't best made by reading a comparison page, it's made in a conversation with a prescriber who can review your full history. You can explore the full Wegovy overview or read more about semaglutide as a medicine if you want more background before that conversation. Our clinical team is also explained in more detail on the clinical team profile page if you'd like to understand who reviews consultations at nume.

If you're ready to find out which option fits your health profile, check your eligibility with a free consultation, reviewed the same day by a GPhC-registered prescriber.