The Difference Between Mounjaro and Wegovy, Explained

Step 1, Understand what each medicine actually does inside the body

Wegovy (semaglutide, by Novo Nordisk) is a GLP-1 receptor agonist. It mimics a gut hormone that signals fullness to the brain, slows the rate at which your stomach empties and reduces appetite. GLP-1 medicines as a class have a substantial evidence base built over more than a decade.

Mounjaro (tirzepatide, by Eli Lilly) goes a step further. It activates both the GLP-1 receptor and a second receptor called GIP, making it the only dual-agonist weight-loss medicine currently licensed in the UK. In practice, that second pathway appears to amplify the appetite-suppressing effect. If you want to explore the difference between Mounjaro and Wegovy at a mechanistic level, that dual-receptor action is the most important place to start.

Ozempic is also semaglutide (the same active ingredient as Wegovy) but it carries a UK licence for type 2 diabetes management, not weight loss. It is not appropriate to use it as a weight-loss medicine, and a regulated UK pharmacy will not prescribe it for that purpose. If you are researching how Mounjaro compares with Ozempic, the licensing distinction is the most important point to understand first.

Step 2, Look at what the clinical trials actually showed

The clearest way to compare the two medicines is through their pivotal trials, and then the head-to-head data that followed.

STEP 1 data are published in the New England Journal of Medicine; SURMOUNT-1 and SURMOUNT-5 are also NEJM publications. NICE reviewed both medicines, its appraisal of tirzepatide (TA1026) notes that indirect comparisons favour tirzepatide, and SURMOUNT-5 confirmed that finding in a direct comparison.

A note on Wegovy's newer 7.2mg dose, approved by the MHRA in April 2026: trials reported around 20.7% average weight loss at that strength, which narrows the gap with tirzepatide's highest dose considerably. For a fuller breakdown of how the two medicines stack up at their respective top doses, the page covering what's the difference between Wegovy and Mounjaro looks at this in more detail. Which pen format and dose is available to you is something a prescriber confirms at consultation, it is not something to assume in advance.

For a more detailed look at the cost angle, the Wegovy vs Mounjaro cost comparison page covers what the price difference typically reflects.

Step 3, Compare eligibility, side-effect profiles and practical differences

Both medicines share the same licensed BMI threshold in the UK: adults with a BMI of 30 or above, or 27 or above alongside a weight-related health condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK clinical guidance. NICE's criteria for NHS access differ between the two medicines, tirzepatide under TA1026 and semaglutide under TA875 each come with their own eligibility rules and service requirements.

Side-effect profiles are similar because both medicines slow gastric emptying. Nausea, constipation, diarrhoea and indigestion are the most commonly reported effects with each; they are typically most noticeable at the start of treatment or after a dose increase and tend to ease over time. The NHS pages on tirzepatide and semaglutide set out both side-effect lists in full.

One practical difference worth knowing: for women taking the oral contraceptive pill, the NHS advises adding a non-oral method of contraception for the first four weeks of Mounjaro and for four weeks after each dose increase, because tirzepatide's effect on gastric emptying may reduce pill absorption. Current guidance does not flag the same concern for Wegovy. People who are weighing this up alongside the trial data often find it helpful to read about what's the difference in Mounjaro and Wegovy before their consultation, so these practical points can be discussed in context.

If you have already been on one and are considering a change, the page on switching between Mounjaro and Wegovy covers what that process involves clinically.

How to reach a decision

Setting the two medicines side by side on a page is useful background. It is not the same as a clinical assessment. A prescriber looks at your weight history, existing conditions, other medicines and personal circumstances before recommending one over the other, or neither. Plenty of people who come to us having already read everything still find the consultation surfaces something they had not considered.

If you tend to order things at the start of the month when payday lands, it is worth knowing that orders placed before 12pm Monday to Friday are dispatched the same day once approved, so the timing of a payday order can genuinely get treatment to you the following morning.

Our prescribers are available seven days a week for aftercare, and every repeat order is clinically reviewed before it goes out. You can read more about how we work on the about us page, or go straight to check your eligibility.