Mounjaro Versus Wegovy: How the Two Leading UK Weight-Loss Injections Compare

Step 1 — understand what each medicine actually does

Wegovy contains semaglutide, a GLP-1 receptor agonist made by Novo Nordisk. It mimics one gut hormone involved in appetite regulation, slows gastric emptying, and reduces how much you feel like eating. It has been in clinical use longer than tirzepatide, with a substantial evidence base built around the STEP trial programme, including STEP 1, published in the New England Journal of Medicine, which reported an average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose.

Mounjaro contains tirzepatide, made by Eli Lilly. It is a dual GIP and GLP-1 receptor agonist — the only medicine of its kind licensed in the UK for weight management. Activating both receptors produces a stronger combined effect on appetite and blood-sugar regulation than either pathway alone. In the SURMOUNT-1 trial, average weight loss reached around 20–21% at the 15mg dose over 72 weeks, and in the subsequent SURMOUNT-5 head-to-head comparison, tirzepatide produced greater average weight reduction than semaglutide 2.4mg, results noted directly in NICE's appraisal of tirzepatide (TA1026).

There is now a higher Wegovy dose available. The MHRA approved a 7.2mg semaglutide maintenance dose, and a dedicated single-dose 7.2mg pen was approved on 14 April 2026. Trial data at that dose reported around 20.7% average weight loss over 72 weeks, narrowing the gap with Mounjaro's highest dose considerably. You can read more about how the two medicines compare on results specifically on our Mounjaro versus Wegovy weight-loss results page.

Step 2, compare the numbers in one place

The table below draws together the key factual differences. Numbers from clinical trials are averages across study populations; individual results vary.

For a more granular look at the semaglutide versus tirzepatide evidence base, this page works through the trial data in detail.

Step 3, check who is eligible for each under UK licensing

Both medicines share broadly similar licensed eligibility criteria: adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as high blood pressure, type 2 diabetes, dyslipidaemia, or obstructive sleep apnoea. Lower BMI thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK clinical guidance. Neither is licensed for people under 18, and neither is recommended during pregnancy, while breastfeeding, or when trying to conceive.

On the NHS, access differs meaningfully. Mounjaro is being rolled out in primary care in phased cohorts under NICE TA1026, from June 2025 for those with BMI 40 or above and four or more qualifying conditions, with further cohorts following in 2026 and 2027. Wegovy is available via specialist weight management services under TA875, with typically long waiting lists. Our treatment overview explains what private access looks like as an alternative.

A private prescription bypasses NHS waiting lists but still requires proper clinical assessment. A prescriber looks at your full health picture, not just your BMI. People sometimes ask whether switching between the two is straightforward; that question comes up often enough that we have answered it separately.

Step 4, practical differences worth knowing before your consultation

Day-to-day, the two injections are similar: once-weekly subcutaneous injection into the abdomen, thigh, or upper arm, rotating sites. Both pens live in the fridge door alongside everyday items until you need them, the cold chain requirement is the same and the room-temperature window (for travel, for example) should always be confirmed in the Patient Information Leaflet, since it is medicine-specific and can change.

Side effects overlap considerably. Both produce a GI-led profile: nausea, loose stools, constipation, indigestion, and reduced appetite are common, particularly at the start of each new dose level. These usually settle within a week or two. The MHRA has flagged acute pancreatitis as a known but infrequent serious side effect of GLP-1 medicines; severe stomach pain radiating to the back warrants urgent medical attention. For a full comparison of side-effect profiles, our semaglutide versus Mounjaro page goes into more depth on that angle.

One practical difference for women: if you take an oral contraceptive pill, clinical guidance recommends adding a non-oral method for the first four weeks of tirzepatide treatment and for four weeks after each dose increase, because absorption of oral medications can be slowed. The same requirement is not established for semaglutide. Discuss this with your prescriber before starting either medicine.

Cost also differs by dose and provider. Because the wegovy versus mounjaro uk pricing question comes up regularly, we have put the full breakdown of what private treatment typically costs on a dedicated cost comparison page. For information on how the two medicines compare to Ozempic, which is semaglutide licensed for type 2 diabetes rather than weight loss, this page explains the distinction clearly.

Which medicine is the right fit depends on your health history, other medicines you take, and clinical factors a prescriber needs to assess. Speak to our prescribers through a free consultation and they will work through the options with you.