Switching Between Mounjaro and Wegovy: What Actually Changes

Step 1: Understand why you want to switch, the reason shapes the clinical decision

Most people who ask about switching fall into one of three groups: those whose results have plateaued on their current medicine, those who are experiencing side effects they'd rather not continue with, and those who've been transferred from another clinic and want to move to a different treatment. Each situation calls for a different clinical approach.

A plateau on semaglutide doesn't automatically mean tirzepatide will restart progress, though the evidence is encouraging. An intolerance to one GLP-1 medicine's GI effects doesn't guarantee the other will be easier to tolerate, because both share a broadly similar gastrointestinal side-effect profile: nausea, diarrhoea, constipation, reflux and fatigue are common with each, particularly after starting or increasing a dose. The NHS tirzepatide patient page and its semaglutide equivalent describe these expected effects in plain language.

What's different about tirzepatide is its mechanism. Mounjaro activates both GIP and GLP-1 receptors; Wegovy acts on GLP-1 alone. That dual action is thought to account for some of the difference in average weight loss seen in trials. Whether that difference matters for you specifically is the clinical question your prescriber is trying to answer. If you're weighing up which to choose, it helps to understand how Mounjaro and Wegovy actually differ from one another before that conversation with your prescriber.

Step 2: Know the evidence gap between the two medicines

The headline comparison is this. In SURMOUNT-1 (72 weeks, 2,539 adults with obesity and no diabetes), tirzepatide at 15mg produced an average body-weight reduction of around 20–21%. In STEP 1 (68 weeks, semaglutide 2.4mg), average reduction was around 15%. The SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025 and discussed in the NICE appraisal of tirzepatide (TA1026), found tirzepatide produced greater average weight loss than semaglutide 2.4mg over 72 weeks in adults with obesity but without diabetes.

That gap narrows with the higher semaglutide dose. The MHRA approved a 7.2mg Wegovy pen in April 2026, with trials reporting around 20.7% average loss over 72 weeks, approaching tirzepatide's results at the highest dose. So the comparison table shifts depending on which dose of each medicine you're comparing.

For a fuller comparison of how the two medicines stack up day-to-day, the Wegovy vs Mounjaro overview covers each pillar in depth.

Step 3: Prepare for what changes (and what doesn't) in your routine

Practically speaking, both medicines are once-weekly subcutaneous injections. If you're switching from one pen to the other, your injection day, your sites (abdomen, thigh, upper arm) and your storage routine stay the same. Both pens live in the fridge; both come out for injection and go back in. The transition that catches people out is the restart on a lower dose.

When moving from Mounjaro to Wegovy (or the reverse), you will almost certainly not begin at the dose equivalent of where you left off. Prescribers typically restart at the lowest tolerated dose on the new medicine to let your system adjust to a different molecular entity. This is sometimes frustrating for patients who've spent months titrating upward. But it reflects a genuine pharmacological consideration: these are different molecules, and tolerance to one doesn't transfer to the other. For the specifics of what that re-titration looks like in practice when going in each direction, switching from Mounjaro to Wegovy and whether switching between them is possible both address this in more detail.

There's also the contraception point. Women on oral contraceptives switching to or increasing Mounjaro should add a non-oral method for the first four weeks of treatment and four weeks after each dose increase, because tirzepatide may reduce pill absorption. That's a specific practical change that doesn't apply in the same way to semaglutide. The NHS England guidance on weight-management injections covers this alongside advice on HRT and surgery.

Step 4: Bring your evidence and get a same-day clinical review

Whether you're moving between treatments, joining nume from another clinic, or asking a prescriber to reconsider your current medicine, what you need is a fresh clinical assessment. At nume, transfer patients provide evidence of their current treatment and most recent dose; dose changes and medicine switches are reviewed before anything is dispatched. A real prescriber, not a routing algorithm, reads your case. You can explore the clinical team behind that process on our prescriber page.

On cost: switching medicines may change what you pay, since Mounjaro and Wegovy carry different prices at different doses. The UK price comparison between Mounjaro and Wegovy explains the current market picture. Neither medicine is the right choice purely on price. The right metric is clinical suitability, supervised by a prescriber who knows your history.

Which of these two medicines suits you is a clinical decision our prescribers make with you. Check your eligibility and start your free consultation.