What switching from Mounjaro to Wegovy is really like

Step 1: Understand why you're considering the switch

Before thinking about timelines or doses, it's worth being precise about the reason. The most common ones our prescribers hear are: a change in Mounjaro's price (Eli Lilly raised its UK list price substantially from September 2025, pushing some private providers' per-month costs significantly higher); side effects that haven't settled as expected; or simply curiosity about whether semaglutide might suit someone better. Each reason points to a different clinical conversation. A price-driven switch, for example, may not always make financial sense once you account for the full cost of Wegovy at an equivalent stage of treatment — the cost difference between Mounjaro and Wegovy is not always straightforward. A side-effect-driven switch needs a careful look at whether the problem is medicine-specific or something adjustable through dose or injection timing. Getting clear on the reason first means the prescriber can give you a genuinely useful answer rather than a generic one.

Step 2: Know what a clinical switch actually involves

Switching is not like changing supermarkets. Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist; semaglutide (Wegovy) acts only on the GLP-1 receptor. The mechanisms overlap but are not identical, which means your body's response to the new medicine may differ from what you experienced on the first. There is currently no published protocol specifying a universal washout period or dose-equivalency rule for switching between the two, which is why prescriber assessment is essential. In practice, most clinicians start the new medicine at its lowest dose to allow your system to adjust, regardless of how far up the titration ladder you had progressed. That can feel like going backwards, and it's worth being prepared for that. You can read a fuller breakdown of how the switch from Mounjaro to Wegovy is approached clinically. The prescriber will also want to know your current weight, any recent dose changes, and whether your weight loss has plateaued, all of which shape the recommendation.

Step 3: Compare the trial evidence side by side

The table below summarises the key clinical data for both medicines as licensed in the UK. These are headline figures from separate trials in different populations; direct comparisons should be read carefully.

The SURMOUNT-5 result is the only published head-to-head data; comparisons involving Ozempic are a separate matter, since Ozempic is semaglutide licensed for type 2 diabetes, not weight management. For a more detailed breakdown of how the two weight-loss medicines compare on mechanism, tolerability and access, the Wegovy vs Mounjaro page covers that in full.

Step 4: Set realistic expectations before you switch

People who switch because Mounjaro stopped working as well as it once did sometimes find Wegovy performs differently, but not always better, and not always for the same reasons. Weight loss from either medicine slows as you approach a new set-point; that's biology, not a product failing. If tirzepatide at its highest tolerated dose has plateaued, the MHRA-approved 7.2mg Wegovy pen is worth discussing with a prescriber, since trial data suggests it narrows the gap with tirzepatide's maximum dose meaningfully. Conversely, some people switch back: if you've looked at whether switching from Mounjaro to Wegovy produces the expected results and found it hasn't, there is a route back, and returning to tirzepatide follows a similar clinical-review process. The 12pm cut-off matters practically here too: if you're managing a repeat order around work and childcare, knowing that a same-day dispatch requires your consultation in before midday means you can plan ahead. At nume, a prescriber reviews every repeat before anything is sent, so the clinical conversation about staying on course or reconsidering continues with every order.