Can You Switch from Wegovy to Mounjaro Straight Away?

Why can't you just stop Wegovy on Friday and start Mounjaro on Monday?

The instinct to switch quickly is understandable. You may have hit a plateau on Wegovy, struggled with side effects, or simply want to try a medicine the evidence suggests can deliver greater average weight loss. Wanting that without a long wait is entirely reasonable.

The clinical hesitation is not about bureaucracy. Semaglutide (the active ingredient in Wegovy) has a half-life of roughly a week, which means it stays active in your system for some time after the last dose. Starting tirzepatide (Mounjaro) before that clears increases the risk of compounding gastrointestinal side effects (nausea, vomiting, diarrhoea) since both medicines slow gastric emptying and reduce appetite through overlapping mechanisms. A prescriber will typically want to know the date of your last Wegovy dose, the dose level you were on, and how well you tolerated it.

There is no single universal washout period written into the UK licences, which is exactly why a prescriber's judgement is required rather than a fixed rule you can apply yourself. The NHS guidance on tirzepatide sets out what patients should expect, but the specific switching question is one for your clinical team. Mounjaro's Summary of Product Characteristics on the electronic Medicines Compendium similarly defers titration decisions to the prescriber.

How do the two medicines actually compare, and does switching make clinical sense?

It is worth grounding the comparison in what the evidence actually says, because the numbers are what most people switching are responding to.

In the SURMOUNT-5 open-label trial (72 weeks, 751 adults with obesity and no diabetes), tirzepatide produced a greater average reduction in body weight than semaglutide 2.4mg. That data has informed NICE's discussion of indirect comparisons in its appraisal of tirzepatide (NICE TA1026). None of this makes Mounjaro the automatic right choice for every person, tolerance, other health conditions and what you managed well on Wegovy all feed into that judgement. You can explore the full Wegovy vs Mounjaro comparison for a deeper look at the evidence side by side.

What dose of Mounjaro would you start on after Wegovy?

This is the question our prescribers hear most often from patients considering a switch: do I have to go back to the beginning?

The licensed starting dose for Mounjaro is 2.5mg, and that dose exists primarily for tolerability, to let your system settle rather than as a therapeutic weight-loss level. Whether someone switching from a higher-dose Wegovy needs to follow the full titration sequence, or whether their clinical picture supports a different approach, depends on factors only a prescriber can assess: how long you have been on GLP-1 treatment, your current weight, any side effects experienced, and the overlap between when your last Wegovy dose was active and when Mounjaro begins.

Skipping steps without guidance is not recommended, and neither is assuming you can maintain the same biological tolerance across two different medicines simply because both are GLP-1-related. Mounjaro also activates GIP receptors, which semaglutide does not, the dual mechanism is clinically meaningful, not just a marketing distinction. If you are considering making that change in the other direction, our guide to how to switch from Mounjaro to Wegovy walks through what that process involves and the clinical factors a prescriber will weigh. If you are curious about the reverse journey, the process for switching from Mounjaro to Wegovy raises a parallel set of questions worth reading.

What should you do next if you want to switch?

If you are currently on Wegovy through another provider and want to move to Mounjaro, the clearest path is a consultation with a prescriber who can review your treatment history properly. At nume, transfer patients are asked to provide evidence of their current treatment, dose, duration and the name of the prescribing service. A named prescriber on our clinical team then reviews that, alongside your current weight and medical history, before any new prescription is written.

You can read about our clinical team and the way oversight works at nume. Every repeat order is re-reviewed before dispatch, there is no automated continuation. People also sometimes ask whether switching from Ozempic to Mounjaro follows the same process, and the considerations around overlapping mechanisms are broadly similar, though the clinical details differ. For those already on Mounjaro who are weighing their options, the question of whether you can switch from Mounjaro to Ozempic is covered separately, including what that change in receptor action means in practice. For a broader look at what switching between GLP-1 medicines involves, the question of switching back from Wegovy to Mounjaro covers the reverse scenario in detail, and the treatment overview sets out what each option involves from the start. Which medicine suits you is a clinical decision our prescribers make with you, not something to determine from a comparison table alone.