Thinking About Switching from Mounjaro to Wegovy?

What actually changes when you move from one medicine to the other?

Mounjaro (tirzepatide) activates two receptors (GIP and GLP-1) involved in appetite regulation and blood-sugar signalling. Wegovy (semaglutide 2.4mg) works on GLP-1 alone. That single difference in mechanism partly explains why their average weight-loss figures differ in the trial data, and it's also why a body that has adapted to one may respond differently to the other.

Both medicines slow gastric emptying, reduce appetite and are given once weekly by subcutaneous injection. The practical routine (injecting from a pre-filled pen, rotating sites between abdomen, thigh or upper arm, keeping the pen refrigerated) is broadly similar. What differs is the titration schedule, the pen format and, for some people, the side-effect profile. A question our prescribers hear most weeks is whether it is actually ok to switch from Mounjaro to Wegovy, and the honest answer is that it isn't a straight swap at an equivalent dose. When moving from Mounjaro to Wegovy (or the other direction), most prescribers restart from the lowest dose to let the body adjust, rather than estimating an equivalent mid-ladder dose. The process of switching between these medicines has specific clinical considerations worth reading before making any decision.

Side effects for both medicines are predominantly gastrointestinal (nausea, loose stools, constipation, reflux) and tend to be most noticeable when starting or stepping up. Individual tolerance varies, and a difference in that profile between the two drugs is sometimes the clinical reason a switch is considered.

How do Mounjaro and Wegovy compare on weight-loss evidence?

The clearest head-to-head data comes from the SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, which compared tirzepatide directly with semaglutide 2.4mg over 72 weeks in adults with obesity and no diabetes. Tirzepatide produced greater average weight reduction. NICE references this evidence in its appraisal of tirzepatide, TA1026, noting that indirect comparisons favour tirzepatide over semaglutide at the licensed weight-management doses.

That said, Wegovy's 7.2mg dose (approved by the MHRA in January 2026 and available as a dedicated single-dose pen from April 2026) narrows the gap considerably, with trials reporting around 20.7% average weight loss over 72 weeks. The comparison below uses published trial figures; individual results will differ.

Numbers in this table are from SURMOUNT-1 and STEP 1, both published in the NEJM, and from MHRA approval announcements for the 7.2mg pen. They describe trial averages, not individual outcomes. Which medicine is right for a particular person depends on clinical factors that go well beyond any single number.

Can you switch from Wegovy to Mounjaro, and does the logic work both ways?

Yes, the question runs in both directions. People established on Wegovy sometimes ask about moving to Mounjaro, perhaps because their weight loss has slowed, because the dual-agonist mechanism is now available to them privately, or because their NHS access changes. The clinical considerations are symmetrical: a prescriber reviews progress on the current medicine, checks for contraindications, and decides whether a switch is appropriate and, if so, what starting dose is safe.

There is no recognised equivalent-dose conversion table between tirzepatide and semaglutide, so restarting from the bottom of the titration ladder is the standard cautious approach. Our page on whether switching between these medicines is appropriate covers the eligibility considerations in more detail. If you've already made a switch and want to understand what to expect next, experiences after switching may be useful reading.

One practical note: if you move from Mounjaro to Wegovy while taking an oral contraceptive pill, the absorption interaction differs between the two medicines. Tirzepatide carries a specific MHRA-noted caution requiring additional contraception for the first four weeks of treatment and after each dose increase; current evidence does not show the same effect with semaglutide. If you're switching direction (from Wegovy to Mounjaro) factor that in when you speak to a prescriber. The NHS England guidance on weight-management injections covers contraception and HRT considerations for both medicines.

How does the decision get made, and what happens at the consultation?

A switch is a clinical decision, not a product choice. The prescriber will typically want to know: how much weight has been lost, at what dose, over what period; whether side effects are driving the request; whether there are any contraindications to the new medicine; and what the patient's expectations are. Modest progress on a current dose, persistent intolerance, or a change in clinical circumstances can all be valid reasons to discuss switching.

At nume every consultation is reviewed by a GPhC-registered Independent Prescriber, not automated software. Transfer patients provide evidence of their current treatment, and any dose change or medicine switch involves a clinical re-review before a prescription is issued. You can read more about whether switching is likely to be right for you, or explore the full range of weight-loss treatments we offer to see what's available through our pharmacy. Our clinical team oversees every prescription issued. Ultimately, which medicine suits you (Mounjaro, Wegovy, or staying on what you're already taking) is a decision the prescriber makes with you, not for you.