Switching from Mounjaro to Wegovy: the decision explained

What you are actually comparing when you switch between these two medicines

Mounjaro and Wegovy are not interchangeable versions of the same drug. They share a family resemblance (both slow gastric emptying, reduce appetite, and are given as once-weekly subcutaneous injections) but the mechanisms differ. Tirzepatide (Mounjaro) is the only dual-agonist licensed for weight management in the UK, acting on both GIP and GLP-1 receptors. Semaglutide (Wegovy) is a GLP-1 agonist alone, and if you are wondering whether Mounjaro contains semaglutide, the short answer is that it does not; they are distinct molecules working in related but different ways. That second receptor is likely why the average weight reductions seen with tirzepatide have, in clinical trials, tended to be larger.

In the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, tirzepatide produced a greater average reduction in body weight than semaglutide 2.4 mg over 72 weeks in adults with obesity who did not have diabetes. NICE's committee discussion of TA1026 notes that indirect comparisons also favour tirzepatide. At the same time, Wegovy's newer 7.2 mg dose (approved by the MHRA in early 2026) has narrowed that gap, with trial data showing around 20.7% average loss over 72 weeks. That context matters if you are weighing up whether moving from Wegovy to Mounjaro, or the reverse, is likely to change your results.

For a structured side-by-side look at the two medicines, the Wegovy vs Mounjaro comparison on this site covers the clinical picture in more detail. The point here is that a switch is not a simple like-for-like substitution; the prescriber needs to understand what you achieved on your current treatment and why you are considering a change.

The three main reasons people consider moving from one to the other

Most people enquiring about a switch fall into one of three situations, and which one applies shapes the clinical conversation quite differently.

The first is tolerability. GI side effects (nausea, loose stools, reflux, fatigue) are common on both medicines, but individual responses vary considerably. Some people find semaglutide easier on their digestion; others find tirzepatide's dual mechanism means a different side-effect profile that suits them better. If you are thinking about moving from semaglutide to tirzepatide for tolerability reasons, that is a valid clinical factor, though the prescriber will also consider whether the side effects settled in time or were persistent.

The second reason is response. If weight loss has plateaued on the highest tolerated dose of one medicine, a prescriber may consider whether the alternative mechanism could produce a different response. This is a clinical judgement, not a guarantee, the evidence for cross-switching to overcome a plateau is not yet as robust as the evidence for each medicine individually.

The third reason is access and continuity. Supply pressures, changing circumstances or a provider change sometimes prompt the question. That is a practical concern, and a legitimate one, but the clinical review process is the same regardless of why you are asking.

If you are coming from the other direction (moving from Mounjaro to Wegovy specifically) it is worth noting that you would typically begin Wegovy at its starting dose (0.25 mg weekly) and titrate upward under prescriber guidance, rather than picking up at an equivalent dose. Your prescriber sets that schedule.

How the two medicines compare on the facts that matter most for this decision

Source: NICE TA1026; NICE TA875; NHS England weight-management injections guidance. Numbers are clinical-trial averages; individual results vary.

What a switch actually involves, and how to approach it safely

Switching medicines is not something to do between repeat orders. A prescriber needs to know your full picture: current dose, how long you have been on it, what your weight trajectory has looked like, any side effects, and whether your weight-related conditions have changed. That review happens before any new prescription is written.

At nume, every repeat order and every change in treatment involves a fresh clinical review. There is no algorithm making that call. If you are considering switching from Mounjaro to Wegovy, or asking whether the reverse might suit you better, the consultation is the place that conversation starts. Our prescribers are familiar with both medicines and with the questions that come up in this situation.

The cost picture is also part of the decision for most people. Mounjaro's UK list price rose significantly from September 2025 (the highest-dose pen's list price moved to around £330 for a four-week supply) and private prices across providers have shifted accordingly. If you want a full comparison of how costs differ between the two medicines, the tirzepatide versus semaglutide cost comparison sets that out clearly. What both medicines share is the same basic requirement: a valid UK prescription, written by a qualified prescriber, following a proper clinical assessment.

Which medicine is the better choice for you is not a question this page can answer. It is exactly the question our prescribers work through with you. Speak to our prescribers and start that conversation today.