Switching medicines: what to know before transferring from Mounjaro to Wegovy

What the trial data actually shows — and why the numbers aren't directly comparable

SURMOUNT-1, published in the New England Journal of Medicine, found that tirzepatide at its highest dose produced around 20–21% average body-weight reduction over 72 weeks in adults with obesity who did not have type 2 diabetes. The STEP 1 trial, also published in the New England Journal of Medicine, found semaglutide 2.4mg produced approximately 15% average reduction over 68 weeks in a similar population. Those trials were run separately, in different cohorts, with slightly different durations, so treating the gap as a simple head-to-head overstates the certainty.

A genuine head-to-head did eventually happen. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, randomised 751 adults with obesity and no diabetes to either tirzepatide or semaglutide 2.4mg for 72 weeks. Tirzepatide produced greater average weight reduction. That evidence was considered by NICE when it appraised tirzepatide in Technology Appraisal TA1026, published December 2024. The NICE committee noted that indirect comparisons across programmes also favoured tirzepatide, though it acknowledged the uncertainty in cross-trial readings.

One point worth knowing: semaglutide now has a 7.2mg maintenance dose, approved by the MHRA on 14 April 2026 as a dedicated single-dose pen. Trials at that dose reported around 20.7% average loss over 72 weeks, bringing it much closer to tirzepatide 15mg results. That approval is recent, and real-world data on the 7.2mg pen is still accumulating.

For someone thinking about the practicalities of this transition, the starting point is understanding that the average-results gap between the two medicines has narrowed, but your individual response, tolerability and clinical history are the figures that actually matter to the prescriber. If you want a closer look at how these two medicines compare on the evidence, our Wegovy v Mounjaro guide sets out the key differences in one place.

Why people switch) and what clinical factors shape the decision

The reasons someone moves from Mounjaro to Wegovy, or considers doing so, are usually practical rather than evidence-driven. Supply constraints on a specific strength. A prescriber's preference given a patient's full medical history. A side-effect profile on one that is better tolerated. Cost differences. Occasionally, a patient who has reached their highest tolerated tirzepatide dose and whose prescriber wants to reassess the treatment plan entirely.

What that transfer looks like clinically is not a straight continuation. Switching between GLP-1 medicines involves a prescriber judging the appropriate restart dose on the new medicine, reviewing your weight, your response to the previous treatment and any side effects you experienced. You would not necessarily pick up at an equivalent strength; the dose ladder on Wegovy runs differently, and someone who had titrated to 10mg or 15mg tirzepatide would need a clinical assessment before any equivalent on semaglutide was chosen.

The practical details of moving from one to the other are worth reading before you speak to a prescriber, because the questions you're likely to ask (how soon can I start, what happens to my progress) have clinical answers rather than fixed timelines. If you're switching because of supply, timing is worth planning around: a Monday order placed before 12pm, for instance, means your replacement treatment can be assessed and dispatched the same day.

Oral semaglutide (Wegovy tablets, approved by the MHRA on 11 June 2026) adds a third option to the conversation. If injection fatigue is part of why a switch is being considered, a prescriber may bring that into the discussion. It requires no refrigeration and a once-daily morning routine, though the dosing schedule and absorption requirements are quite different from the injections.

The side-effect and contraception picture when switching

Both medicines carry a GI-led side-effect profile: nausea, diarrhoea, constipation and reflux are the most commonly reported, and they tend to be most noticeable when starting or moving up a dose. Switching medicines can effectively reset that adjustment period, so someone who found the first weeks on Mounjaro uncomfortable should expect something similar at the start of Wegovy, not a smooth continuation.

There is a specific contraception consideration for Mounjaro that does not carry the same weight for semaglutide. Women taking the oral contraceptive pill while on tirzepatide are advised to use an additional non-oral method for the first four weeks of treatment and for four weeks after each dose increase, because tirzepatide slows gastric emptying in a way that may reduce pill absorption. If you are transitioning from Mounjaro to Wegovy, it is worth knowing that NHS guidance notes there is no equivalent evidence of this effect with semaglutide, so for some patients that consideration actually becomes simpler after a switch. The NHS England guidance on weight-management injections covers this in detail and is worth reading before your consultation.

The MHRA highlighted acute pancreatitis as a known, though infrequent, side effect of GLP-1 medicines in a Drug Safety Update in January 2026. Severe stomach pain that extends to the back, with or without vomiting, is the symptom to act on urgently regardless of which medicine you are taking. Suspect side effects from either product can be reported at the MHRA's Yellow Card site.

If you have questions specific to your own medical history, our clinical team is one place to start. You can read more about how our prescribers approach these decisions before you fill in your consultation.

Which medicine is right for you, and what happens at the consultation

The evidence leans one way in average terms, but averages conceal a lot. Individual response to tirzepatide and semaglutide varies considerably, and some people tolerate one far better than the other or have contraindications that rule a specific medicine out. A prescriber weighing a transfer request is looking at your whole picture: current dose, reason for switching, weight trajectory, comorbidities, contraceptive method, any other medicines you take and how long you have been on treatment.

At nume, every prescription request, including a switch from one GLP-1 to another, is read by a real GPhC-registered prescriber on the day it arrives. There is no algorithm making that call. Transfer patients are asked for evidence of their current or most recent treatment, and any dose change requires clinical review rather than assumption. Our guidance on moving from Mounjaro to Wegovy covers the eligibility, cost and practical differences in more depth if you want to read further before booking, and our Mounjaro to Wegovy overview is a useful companion if you want a broader summary alongside it.

Which medicine suits you is a clinical decision made with our prescribers, not something that can be resolved by a webpage. Start your free consultation and one of our team will review your situation the same day.