Switching from Mounjaro to Wegovy — how long do you actually need to wait?

The myth: you need weeks off before starting Wegovy

The idea of a multi-week gap between Mounjaro and Wegovy is one of the most persistent misconceptions our prescribers encounter. It probably originates from confusion with medicines that genuinely require washout periods due to irreversible enzyme inhibition or narrow therapeutic windows. GLP-1 and dual GIP/GLP-1 medicines do not fall into that category.

Both tirzepatide (Mounjaro) and semaglutide (Wegovy) are eliminated from the body over roughly four to five weeks, with half-lives of around five to seven days for semaglutide and approximately five days for tirzepatide. Waiting several weeks would mean a prolonged gap during which appetite regulation reverts and any weight regained tends to come back quickly, research consistently shows that stopping GLP-1 treatment without a plan leads to significant rebound. A gap that long is generally not in your interest unless there is a specific clinical reason.

The practical rule: take your last Mounjaro dose, then begin Wegovy on the day the next Mounjaro injection would have fallen. That preserves continuity of effect while avoiding stacking two active doses. If you missed a Mounjaro dose before the switch, tell your prescriber, as the guidance on how long to wait when switching between GLP-1 medicines shows that timing can shift slightly depending on your circumstances.

What changes when you switch, and why it matters for your starting dose

Mounjaro activates two receptors, GIP and GLP-1. Wegovy targets GLP-1 only. That difference in mechanism means the two medicines are not straightforwardly interchangeable at the same "strength", even though both produce meaningful weight loss. A detailed comparison of tirzepatide and semaglutide by mechanism and trial results is worth reading before your consultation.

In SURMOUNT-1 (2,539 adults, 72 weeks), tirzepatide at 15mg produced average body-weight reductions of around 20–21% [SURMOUNT-1, NEJM]. The STEP 1 trial for semaglutide 2.4mg reported around 15% average reduction at 68 weeks [STEP 1, NEJM]. The MHRA-approved 7.2mg Wegovy dose, available since early 2026, narrows that gap (trials reported roughly 20.7% average loss over 72 weeks) but the head-to-head SURMOUNT-5 trial (published in NEJM, 2025) still found tirzepatide produced greater average weight reduction than semaglutide 2.4mg.

Because Wegovy starts at 0.25mg regardless of what dose of Mounjaro you were on, your prescriber needs to know your full dose history. Someone stepping down from 15mg tirzepatide will have different tolerability expectations than someone who only reached 5mg. Describing how you got on (particularly any GI side effects) takes under a minute and shapes the plan meaningfully. If Wegovy feels less effective after switching, that context is exactly what your prescriber needs.

How the switch works in practice at a regulated UK pharmacy

People switch for various reasons, Mounjaro stock issues, tolerability, cost, or a prescriber's clinical recommendation. Whatever the reason, the process through a GPhC-registered pharmacy follows a clear path. Your prescriber reviews your treatment history, confirms clinical suitability for Wegovy, and issues a prescription. There is no algorithmic rubber-stamp; our clinical team reads each case individually.

For people coming from another provider, transfer patients provide evidence of their current treatment before any prescription for a new medicine is issued. That is an MHRA-aligned safeguard, not a hurdle. A quick check worth doing right now: search the GPhC register at pharmacyregulation.org/registers and confirm that any pharmacy you are considering (including us) holds a valid premises registration. Ours is 9012878. That one check takes under a minute and filters out the majority of illegitimate sellers.

Precise timing guidance for the gap between your last Mounjaro and first Wegovy dose depends on your individual situation. Similarly, the question of how soon you can begin Wegovy after stopping Mounjaro often comes down to why you stopped rather than a fixed calendar rule. Both questions are answered in detail on those pages. Which medicine suits you long-term is a clinical decision made with your prescriber, not one this page (or any content page) can make for you.

If you are ready to discuss a switch, or starting treatment for the first time, start your free consultation and a prescriber will review your case the same day.