Does switching from Mounjaro to Wegovy actually work?

The biggest misconception: that Wegovy is simply 'the same thing'

A lot of people assume Mounjaro and Wegovy are interchangeable, different brands, same drug. They're not. Mounjaro contains tirzepatide, a dual GIP and GLP-1 receptor agonist. Wegovy contains semaglutide, which targets GLP-1 receptors only. The two-pathway mechanism in tirzepatide is the reason trial data has consistently shown a larger average weight reduction for Mounjaro at its highest doses. In SURMOUNT-5, a 72-week head-to-head trial published in the New England Journal of Medicine (2025), tirzepatide produced greater average weight loss than semaglutide 2.4mg in adults with obesity and no diabetes. If you're weighing up the options, our page on whether Wegovy works better than Mounjaro looks at that evidence in detail and is worth reading before drawing conclusions.

That said, "different" doesn't mean "worse for you". Some people respond better to semaglutide; tolerance, individual biology, and how each medicine fits your circumstances all play a role. The misconception to correct isn't that switching is pointless, it's that switching is simply a label swap. It isn't. You're changing the mechanism, and your body will notice.

The Wegovy vs Mounjaro comparison on this site covers the mechanism difference in more depth if you want to read further before speaking to a prescriber.

When does switching from Mounjaro to Wegovy make clinical sense?

A question our prescribers hear most weeks goes something like this: "I've been on Mounjaro but my previous clinic is closing / my GP won't prescribe it / I had side effects I couldn't manage, can I try Wegovy instead?" The honest answer is: sometimes yes, and the reasons matter.

Clinically, a switch might make sense if you experienced side effects on tirzepatide that you didn't tolerate, if supply or prescribing access is disrupted, or if your prescriber judges that a GLP-1-only approach suits your medical history better. What it is unlikely to do is produce more weight loss than Mounjaro at an equivalent maintenance dose, the trial evidence points the other way. The STEP 1 trial reported around 15% average body-weight reduction over 68 weeks with semaglutide 2.4mg; SURMOUNT-1 showed approximately 20–21% at tirzepatide 15mg. Both figures are trial averages in specific populations, cited here from NICE's appraisal of tirzepatide (TA1026), not predictions for any individual.

Switching because you've read that Wegovy is cheaper, or because a particular dose of Mounjaro is out of stock, is a different calculation, and it's one worth discussing with a prescriber rather than acting on unilaterally. If you are considering making that move, our guide on how to switch from Mounjaro to Wegovy covers what that process looks like step by step.

How the two medicines compare: a factual snapshot

The table below summarises the key clinical facts. Numbers are sourced from NICE TA1026 and TA875, and the respective published trial data.

The cost comparison between tirzepatide and semaglutide is a separate question worth reading if price is part of your thinking.

What to expect if a switch is agreed, and what happens if you want to go back

If a prescriber decides a switch is appropriate, you don't simply swap one pen for the other at your current dose. Semaglutide is titrated differently from tirzepatide; a prescriber will set a starting point based on your history, tolerance, and current weight. You may restart a lower dose during the adjustment period. Expect the first few weeks on Wegovy to feel different, the GI side-effect profile is broadly similar (nausea, changes in bowel habit, reduced appetite) but the intensity and timing can vary between individuals.

If the switch doesn't work out, going back is possible but again requires clinical review. The guide on switching back to Mounjaro from Wegovy covers what that route involves. And if you're coming from Ozempic rather than Mounjaro, the clinical picture is different again, Ozempic is licensed for type 2 diabetes, not weight management, so that page addresses a distinct situation.

The NHS tirzepatide page and its semaglutide equivalent are useful plain-English references for both medicines' side-effect profiles as you think this through. At nume, every switch request is reviewed by a real prescriber, your consultation goes to a named clinician, not an automated triage system. Check your eligibility and start a free consultation if you'd like a clinical view on your specific situation.