How Long After Mounjaro Can You Take Wegovy — and Does the Switch Make Sense?

Why you are switching matters more than when you last injected

A question our prescribers hear most weeks: "I've been on Mounjaro for six months, can I just swap to Wegovy?" The honest answer is that the one-week washout window is the easy part. The harder question is what is driving the switch.

Tirzepatide (Mounjaro) acts on two gut-hormone receptors, GIP and GLP-1. Semaglutide (Wegovy) targets only the GLP-1 receptor. When the body has adapted to dual-pathway stimulation, stepping across to a single-pathway medicine often feels like a reduction in effect, appetite control can loosen, and some people notice weight regain in the first few weeks. If Wegovy seems less effective after Mounjaro, that is a recognised pattern, not a sign the medicine is faulty.

Common reasons people consider switching include: side-effect profile differences, availability, cost, or a prescriber's clinical recommendation. Each of those reasons points toward a different conversation. If side effects on tirzepatide are the driver, a prescriber needs to know which effects, at which dose, and for how long, before deciding whether semaglutide is likely to be any better. These are not questions an online forum can answer reliably.

Whatever the reason, the clinical process for switching from Mounjaro to Wegovy should be managed by the prescriber overseeing your treatment. They hold the clinical context. Timing the first injection yourself, without that conversation, carries real risk of overlap or under-dosing.

What the evidence says about the two medicines' results

This is a COMPARE page, so the evidence deserves a direct look. In the SURMOUNT-1 trial (2,539 adults with obesity, 72 weeks), tirzepatide at 15mg produced an average body-weight reduction of around 20–21%, with some analyses reaching higher, results that led NICE to recommend it for NHS use in its Technology Appraisal TA1026, published December 2024. In the STEP 1 trial (68 weeks, semaglutide 2.4mg), average weight reduction was approximately 15%, as published in the New England Journal of Medicine (2021).

The SURMOUNT-5 head-to-head trial, published in the NEJM in 2025, directly compared tirzepatide against semaglutide 2.4mg in 751 adults with obesity over 72 weeks. Tirzepatide produced greater average weight loss. That gap narrows somewhat at Wegovy's newer 7.2mg dose, approved by the MHRA in 2026, which showed approximately 20.7% average weight loss in trials, placing it closer to tirzepatide 15mg territory.

Numbers from trials are averages across populations. Your result on either medicine depends on dose reached, adherence, diet, activity and individual biology. No figure on this page is a prediction of what you will lose. You can read more about how Wegovy and Mounjaro compare across a broader set of factors, including side-effect profiles and eligibility criteria.

Switching in the other direction: Ozempic is not the same as Wegovy

One point worth making clearly: Ozempic is also semaglutide, but it is licensed in the UK for type 2 diabetes, not weight management. If your question is about switching between Mounjaro and Ozempic for weight loss, Ozempic is not the right medicine for that purpose. The timing question around Ozempic and Mounjaro is sometimes asked by people who have been on Ozempic off-label, a separate clinical situation that always needs prescriber input.

Similarly, Rybelsus (oral semaglutide) is licensed for type 2 diabetes in its available strengths; the oral semaglutide medicine licensed for weight management is Wegovy tablets, approved by the MHRA in June 2026. These are different products and should not be treated as interchangeable.

What the decision looks like in practice, and how to make it safely

Switching from Mounjaro to Wegovy is not a one-line answer. It is a clinical decision shaped by your current dose, how long you have been on treatment, what prompted the switch, and what dose of Wegovy would be appropriate to start at. A prescriber cannot safely determine any of those things without seeing your record.

Stopping treatment of any kind carries its own risk: research on what happens after stopping both medicines is clear that most weight returns without continued treatment or significant lifestyle changes, something worth reading about before making a switch driven by short-term factors. The evidence on weight regain after stopping GLP-1 treatment is sobering enough to factor into this decision.

Cost is another reason people consider switching. The price difference between tirzepatide and semaglutide has shifted since Eli Lilly raised Mounjaro's UK list price from September 2025. You can see a factual breakdown on the Mounjaro vs Wegovy price comparison page. At nume, at nume, one transparent price covers consultation, prescription, treatment and aftercare, with no subscription pulling the next pen out automatically.

Which medicine suits you is a clinical decision our prescribers make with you, based on your full picture. Check your eligibility and start a free consultation, a named prescriber reviews your answers the same day.