Changing from Mounjaro to Wegovy: the facts without the guesswork

The biggest misconception: swapping pens is not the same as swapping medicines

Many people assume that because Mounjaro and Wegovy are both weekly injections used for weight loss, moving from one to the other is essentially an administrative step. It isn't. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — the only weight-loss medicine licensed in the UK that activates two gut-hormone pathways simultaneously. Wegovy (semaglutide) targets the GLP-1 receptor alone. That difference in mechanism means the medicines are not interchangeable without thought, and it matters clinically when a prescriber considers your history, your current dose, and how your body has responded.

The practical upshot: changing from Mounjaro to Wegovy is not a like-for-like dose substitution. There is no official conversion table in the UK prescribing guidance because the two medicines have different potency profiles across their respective dose ladders. A prescriber reviewing the switch will typically restart Wegovy from its initial dose, using the titration schedule set out in the Wegovy SmPC, rather than mapping across from, say, 7.5mg tirzepatide to an assumed equivalent semaglutide dose. The NHS Mounjaro medicines page and the Wegovy patient information on the NHS both confirm these as distinct medicines with separate dosing pathways.

That restart can feel frustrating if you were well-established on a higher Mounjaro dose. It does, however, protect against side effects that can be intensified by jumping too far up the semaglutide ladder too quickly. Worth knowing before you decide.

What the evidence says about weight loss on each medicine

There is now direct head-to-head trial evidence. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, ran 72 weeks in adults with obesity and no diabetes. Tirzepatide produced a greater average reduction in body weight than semaglutide 2.4mg over that period. NICE's technology appraisal of tirzepatide (TA1026) notes that indirect comparisons also favour tirzepatide. The table below summarises the headline figures from the pivotal trials.

Two things to hold onto from those numbers. First, at the highest licensed dose, Wegovy 7.2mg narrows the gap with tirzepatide 15mg considerably, so the difference is not as stark as older comparisons suggested. Second, these are group averages from clinical trials; individual responses vary, and how someone does on one medicine tells you relatively little about how they will do on the other. If you want a deeper side-by-side breakdown, the Wegovy vs Mounjaro comparison page covers the evidence at length.

Reasons people consider changing, and whether the switch typically helps

The most common reasons for changing from Mounjaro to Wegovy (or, for that matter, making the reverse switch from semaglutide to tirzepatide) tend to fall into a handful of categories: tolerance (side effects that don't settle), efficacy (weight loss that has plateaued), cost or supply, or a clinical recommendation following a health change.

Cost is increasingly part of the conversation. Eli Lilly raised Mounjaro's UK list price from September 2025; reported private market prices for the higher doses now typically range from around £149 to £375 per month depending on dose and provider. Wegovy pricing occupies a similar range. The Mounjaro versus Wegovy price comparison has the current context, and for the reasons behind the gap specifically, this page on Mounjaro's pricing explains the factors at play.

Whether switching actually resolves a plateau is genuinely uncertain. Some people find a change of mechanism reignites progress; others don't see a meaningful difference. That uncertainty is not a reason to stay on something that isn't working, but it is a reason to have the conversation with a prescriber rather than assuming the grass is greener. The patient experience page collects what people report, without the clinical claims.

What a prescriber considers before approving a switch

A prescriber reviewing a request to change from Mounjaro to Wegovy will look at: your current dose and how long you've been on it, your weight trajectory, any side effects you've experienced, and any contraindications or interactions relevant to semaglutide specifically. The contraception note is one that catches people out: NHS guidance indicates that for tirzepatide, women on oral contraceptives should use an additional non-oral method for the first four weeks of treatment and after each dose increase, because absorption of the pill can be affected. Semaglutide does not carry the same evidence-based caveat, so switching may simplify that aspect of your regimen. NHS England's weight management injections guidance covers the contraception and HRT considerations for both medicines.

If you're considering the reverse (changing to Wegovy from Mounjaro for a specific clinical reason) the same prescriber-led process applies. Neither direction is a self-service decision.

At nume, a real clinician reads every case. Your consultation details go to a GPhC-registered Independent Prescriber who reviews it personally on the same day; the decision on suitability, and on where your Wegovy dose would start, is theirs to make with you. Verify our pharmacy registration on the GPhC register (9012878) if you'd like to confirm what you're dealing with before you start. For a broader look at the treatment options available, the weight-loss overview is a good starting point.

Which medicine suits you is a clinical decision our prescribers make with you, not something a web page can settle.