Wegovy vs Mounjaro in the UK: how do they compare?
How each one works, what the only head-to-head trial found, how side effects compare, and how NHS access differs. Neither is ranked; a prescriber decides.
Written for the UK. Reading from India? India version
Both are weekly injections licensed in the UK for weight. Mounjaro (tirzepatide) acts on two gut-hormone receptors; Wegovy (semaglutide) acts on one. In the only head-to-head trial, average weight loss was 20.2% on Mounjaro and 13.7% on Wegovy over 72 weeks. On the NHS, GPs can prescribe Mounjaro; Wegovy for weight comes from specialist services.
Key takeaways
- In SURMOUNT-5, the only head-to-head weight trial, adults without diabetes lost an average of 20.2% of their body weight on Mounjaro and 13.7% on Wegovy over 72 weeks; Lilly funded it.1
- Nausea was about as common on both in that trial: 163 of 374 people on Mounjaro and 167 of 376 on Wegovy.2
- On the NHS in England, Mounjaro can be prescribed in primary care, while Wegovy for weight stays in specialist services for up to 2 years.3,4
- Wegovy also has a UK licence and NICE backing to cut heart-attack and stroke risk in people with heart disease and a BMI of 27 or more.5,6
- Mounjaro can make the contraceptive pill less reliable, so the MHRA advises adding a barrier method for 4 weeks after starting and after each dose rise.7
- GLP‑1 medicines are prescription-only medicines in the UK, never sold over the counter.8
- Ozempic and Rybelsus are licensed for type 2 diabetes only, not for weight loss.7
- A prescriber decides whether a medicine fits, which one and at what dose. Nothing here is a recommendation.
- The risks are the same however you get it: see our side effects guide.
On this page
How do Wegovy and Mounjaro work?
Both copy gut hormones that help you feel full; Mounjaro acts on two hormone receptors (GIP and GLP-1), Wegovy on GLP-1 alone.9,10
GLP-1 is a hormone your gut releases after you eat. Semaglutide copies it and acts on the brain areas that control appetite, so people feel fuller for longer.10 Tirzepatide acts on GLP-1 receptors and on a second gut-hormone receptor, GIP.9
Both slow how fast your stomach empties.11,12 Both are weekly injections that begin low and step up. Wegovy goes from 0.25 mg to 2.4 mg over 16 weeks, with 7.2 mg possible later.12 Mounjaro goes from 2.5 mg up to 15 mg, in steps of at least 4 weeks.13
Ozempic is the same medicine as Wegovy. In the UK it is licensed for type 2 diabetes only, not weight loss.7 Our guide to what GLP‑1 medicines do explains the hormones.
What did the head-to-head trial find?
In SURMOUNT-5, weight fell by an average of 20.2% on Mounjaro and 13.7% on Wegovy over 72 weeks.1
The trial gave 751 adults with obesity, but without diabetes, the highest dose each person could tolerate. That meant Mounjaro 10 or 15 mg, or Wegovy 1.7 or 2.4 mg.1 It was open-label: everyone knew which medicine they had.1
Waists shrank by 18.4 cm on Mounjaro and 13.0 cm on Wegovy.1 For a 100 kg (15 st 10 lb) person, 20.2% is about 20 kg and 13.7% about 14 kg. These are averages, and Lilly, which makes Mounjaro, funded the trial.1
Each medicine also beat a dummy injection (placebo) in its own trials. Separate trials can’t be compared directly, because the people and methods differ. In STEP 1, Wegovy 2.4 mg gave −14.9% against −2.4% over 68 weeks.12 In SURMOUNT-1, Mounjaro gave −16.0% to −22.5% against −2.4% over 72 weeks.11 Wegovy 7.2 mg, a newer dose, gave −18.7% against −3.9% on placebo in STEP UP; see our 7.2 mg post.12
How do the side effects compare?
Similar in kind and, in the head-to-head trial, similar in rate: about 44 in 100 people felt sick on each.2
Out of every 100 people in each group of SURMOUNT-5:2
- Felt sick (nausea): about 44 on Mounjaro, against about 44 on Wegovy.
- Vomited: about 15 on Mounjaro, against about 21 on Wegovy.
- Had diarrhoea: about 24 on Mounjaro, against about 23 on Wegovy.
- Had a serious adverse event (a serious medical problem during the trial, of any cause): about 5 on Mounjaro, against about 3 on Wegovy.
SURMOUNT-5 results posted on ClinicalTrials.gov: 374 people on Mounjaro, 376 on Wegovy. Our figures per 100, rounded.2
Two label differences matter in daily life. The MHRA advises Mounjaro users on the pill to add a barrier method, such as condoms. This lasts 4 weeks after starting and after each dose rise.7 Before a planned pregnancy, the MHRA advises stopping Wegovy at least 2 months ahead, and Mounjaro 1 month ahead.7
At Wegovy 7.2 mg, 21.6% reported altered skin sensation, such as tingling or burning, against 0.3% on placebo.12 Our Mounjaro side effects post goes further.
- Stomach effects. In the main trials, about 44 in 100 people on Wegovy 2.4 mg felt sick (nausea), against about 16 in 100 on a dummy injection. On Mounjaro it was about 25 to 29 in 100, against about 9 in 100 on a dummy injection. It mostly comes while the dose goes up.12,11
- Gallbladder problems. Gallstones were reported in about 16 in 1,000 people on Wegovy 2.4 mg. Acute gallbladder disease affected about 20 in 1,000 on Mounjaro, against about 16 in 1,000 on a dummy injection.12,11
- Pancreatitis (an inflamed pancreas): severe stomach pain that won’t go away and may spread to the back. The MHRA updated its guidance on it in January 2026.14
- Dehydration from vomiting or diarrhoea can harm the kidneys.11,12
- Surgery and pregnancy. Tell the team before any anaesthetic. The MHRA advises stopping semaglutide at least 2 months before a planned pregnancy, tirzepatide 1 month.7
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How does NHS access differ?
In England, GP practices can prescribe Mounjaro to the current priority groups; Wegovy for weight comes only from specialist services, for up to 2 years.3,16,4
NICE says Mounjaro “can be used in primary care or specialist weight management services”.3 Wegovy for weight is limited to specialist services and a maximum of 2 years.4 See Mounjaro on the NHS and Wegovy on the NHS.
Wegovy has a second NHS route. NICE backs it for adults with heart disease and a BMI of 27 or more. The aim is fewer heart attacks and strokes.6 In its trial, major heart events (heart attack, stroke or death from heart disease) happened to about 65 in 1,000 people on Wegovy, against 80 in 1,000 on a dummy injection.5
On an NHS prescription, either costs the same: £9.90 per item in England, free in the other nations.17,18,19,20 List prices are in our cost post.
Who decides which one is used?
Your prescriber, weighing your health, your other medicines, any pregnancy plans and what your NHS area offers.
The labels flag factors a prescriber weighs. Neither has been studied in people who have had pancreatitis, so both labels urge caution.11,12 Heart disease points to Wegovy’s heart licence.5 The pill interaction applies to Mounjaro.7
Write down your questions before the appointment. Our guide to seeing a doctor lists what to bring.
Questions people ask
Is Mounjaro stronger than Wegovy?
In SURMOUNT-5, average weight loss was 20.2% on Mounjaro and 13.7% on Wegovy over 72 weeks. That is one open-label trial, funded by Lilly.1
Which has more side effects, Wegovy or Mounjaro?
In SURMOUNT-5 the rates were close. About 44 in 100 felt sick on each, and about 24 in 100 on Mounjaro had diarrhoea, against 23 in 100 on Wegovy. Vomiting affected about 15 in 100 on Mounjaro, against 21 in 100 on Wegovy.2
Is Ozempic the same as Wegovy?
It is the same medicine, semaglutide. In the UK, Ozempic is licensed for type 2 diabetes only, not weight loss.7
Can my GP prescribe Wegovy instead of Mounjaro?
Not for weight on the NHS. NICE has not approved Wegovy for GP or community settings; it is given in specialist services.16,4
Does Mounjaro affect the contraceptive pill?
It may. The MHRA advises adding a barrier method for 4 weeks after starting Mounjaro and after each dose increase. Switching to a non-oral method is the alternative.7
How we researched this
We used the UK labels (SmPCs on the electronic Medicines Compendium) and the SURMOUNT-5 paper and posted results. We also used NICE and MHRA guidance, all opened on 12 October 2026.
Trial figures name the trial, dose and length. Results from separate trials are not compared with each other. We don’t rank the medicines: the right one depends on the person.
Before you move on
- Compare the same type of evidence: the head-to-head trial, not separate trials.
- Check how the pill interaction affects you if you use one.
- Note the pregnancy gap for each: 2 months or 1 month.
- Ask which one your NHS area actually offers.
- Bring your full medicine list to the appointment.
More from the UK blog
The monthly UK update
An independent guide to GLP‑1 medicines. We don’t sell medicines, take drug-company money, earn commissions or link to any provider. Once a month: NHS changes, approvals, list prices and safety alerts. How we write
Sources
- Aronne LJ et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med 2025;393:26–36. PMID 40353578. Link
- ClinicalTrials.gov. NCT05822830 (SURMOUNT-5), posted results: adverse events. Link
- NICE. Tirzepatide for managing overweight and obesity, technology appraisal TA1026, section 1 (recommendations and “What this means in practice”). Published 23 December 2024, last updated 1 September 2025. Link
- NICE. Semaglutide for managing overweight and obesity, technology appraisal TA875, section 1. Published 8 March 2023, last updated 4 September 2023. Link
- MHRA. MHRA approves GLP-1 receptor agonist semaglutide to reduce risk of serious heart problems in obese or overweight adults. Press release, 23 July 2024. Link
- NICE. Semaglutide for reducing the risk of major adverse cardiovascular events in people with cardiovascular disease and overweight or obesity, technology appraisal TA1152. Published 7 May 2026. Link
- MHRA. GLP-1 medicines for weight loss and diabetes: what you need to know. Guidance, published 5 June 2025, updated 5 February 2026. Link
- MHRA. UK first in Europe to authorise orforglipron for weight management and type 2 diabetes. Press release, 10 August 2026. Link
- MHRA. Drug Safety Update: Falsified Mounjaro (tirzepatide) KwikPen 15mg pre-filled pens. 24 February 2026. Link
- MHRA. First GLP-1 tablet for weight loss approved in the UK. Press release, 11 June 2026. Link
- Eli Lilly. Mounjaro KwikPen: UK summary of product characteristics (SmPC), electronic Medicines Compendium. Date of revision 29 August 2026. Link
- Novo Nordisk. Wegovy FlexTouch: UK summary of product characteristics (SmPC), electronic Medicines Compendium. Date of revision 09/2026. Link
- MHRA. MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss. Press release, 8 November 2023. Link
- MHRA. MHRA updates guidance for GLP-1 prescribers and patients. Press release, 29 January 2026. Link
- NHS. When to call 999. Link
- NHS Cheshire and Merseyside (integrated care board). Tirzepatide (Mounjaro) for obesity: information for patients from 1 April 2026. Link
- NHS Business Services Authority. NHS Prescription Prepayment Certificate (PPC). Link
- Scottish Government. Help with health costs (HCS2): quick guide; and Citizens Advice Scotland, Help with health costs. Link
- Welsh Government. Free prescriptions. Link
- nidirect (Northern Ireland government). Help with health costs. Link
Last checked 12 Oct 2026 · Next review due 12 Apr 2027 · Report an error
How this post was made. Written by the GLP Guidebook team from the sources above. It’s general information, not medical advice. Talk to your GP, pharmacist or prescriber before starting, stopping or changing any medicine. We don’t sell, prescribe or recommend any brand or provider. How we write