Thinking of switching from Mounjaro to semaglutide? Here is what to weigh up first

What is actually different between Mounjaro and semaglutide?

The practical question behind most switching decisions is whether one medicine is likely to work better, or sit better, than the other. Mounjaro (tirzepatide) activates two gut-hormone receptors, GIP and GLP-1, whereas semaglutide (sold as Wegovy for weight management) activates the GLP-1 receptor only. Both slow gastric emptying and reduce appetite; the dual mechanism of tirzepatide is thought to account for the difference in average results seen in clinical trials.

In the SURMOUNT-1 trial, adults taking tirzepatide at the highest dose achieved around 20–21% average weight reduction over 72 weeks. The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, showed tirzepatide produced greater average weight loss than semaglutide 2.4mg over the same period, and if you want to evaluate the healthcare company Novo Nordisk alongside Eli Lilly when weighing up these two medicines, that context can help frame the clinical picture. For context on how semaglutide performs, a detailed comparison of Wegovy and Mounjaro sets out the trial figures side by side.

The side-effect profiles overlap considerably: nausea, constipation, diarrhoea and indigestion are common to both, typically most noticeable at the start of treatment or after a dose increase. Some people find one tolerability profile suits them better than the other. That is a legitimate clinical reason to consider switching, and it is one a prescriber can help you unpick.

Neither medicine is suitable for use in pregnancy, breastfeeding, or for those actively trying to conceive. Both are recommended by NICE for eligible adults, though the criteria differ between the two appraisals.

Why people switch from Mounjaro to semaglutide, and the other way around

The reasons for switching run in both directions. Someone moving from Mounjaro to Wegovy might be responding to a change in availability, a prescriber's recommendation based on a comorbidity, or a preference for the semaglutide tolerability profile at a particular dose. Someone switching from semaglutide to tirzepatide is more often doing so because their weight loss has plateaued, because the head-to-head trial evidence has prompted a clinical review, or because Mounjaro has become available to them through a new route.

A question our prescribers hear regularly: can you simply swap one pen for the other without a break? The answer is nuanced. There is no standard washout period enshrined in UK guidance, but the prescriber needs to assess where you are in your current titration schedule, how your body has responded, and what dose is appropriate to start on for the new medicine. Switching from Mounjaro to Wegovy specifically covers this in more detail, including what to tell your prescriber before the change.

Cost is another factor. Comparing the cost of Mounjaro and Wegovy is worth doing before assuming one is more affordable at your dose, since private prices vary by strength and provider. Following Eli Lilly's list price increase from September 2025, typical private Mounjaro prices range roughly £149–£375 per month by dose; Wegovy pricing is in a similar range depending on the pen format. Those figures should be treated as reported context, not fixed quotes.

What the prescriber needs to know before approving a switch

Switching between these medicines is not a simple pharmacy swap. A prescriber reviewing your request will want to know your current dose and how long you have been on it, your recent weight trajectory, any side effects you have experienced, and whether there are clinical reasons that favour one medicine over the other. At nume, a real clinician reads your answers the same day, rather than passing them to automated triage.

If you are currently being treated by another provider and want to switch to a different medicine through nume, you will need to provide evidence of your current treatment. That is standard clinical practice, not red tape: it protects you from being restarted at the wrong dose or from a prescriber missing something relevant from your history. The full clinical picture on switching between these two medicines sets out what documentation is typically needed.

Women taking oral contraceptives should be aware that tirzepatide may reduce pill absorption in the first four weeks of treatment and for four weeks after each dose increase; NHS guidance suggests adding a non-oral method during those periods. There is no equivalent evidence for the same interaction with semaglutide, but any hormonal contraception question should be raised at the consultation rather than assumed away. The NHS England guidance on weight-management injections covers this clearly.

Which medicine fits your situation better is a clinical decision. Our prescribers work through the relevant factors with you rather than defaulting to whichever option happens to be in stock. If you are ready to explore your options, checking your eligibility takes a few minutes and carries no obligation.