Switching between Wegovy and Mounjaro — what the evidence says

Why do people switch from Wegovy to Mounjaro?

Commonly cited reasons include a weight-loss plateau on the current medicine, tolerability issues that prompt a change of molecule, supply variability affecting a specific product, or clinical judgement informed by comparative trial evidence such as SURMOUNT-5. Switching in the reverse direction — from tirzepatide to semaglutide — also occurs, for similar reasons including cost, tolerability, or NHS pathway availability. None of these reasons implies that switching is automatically appropriate for a given individual; it remains an individualised clinical decision.

What does SURMOUNT-5 tell us about switching?

SURMOUNT-5 was a Phase 3 head-to-head trial comparing tirzepatide against semaglutide 2.4 mg in adults with obesity, and it reported a greater mean percentage body-weight reduction with tirzepatide over the 72-week study period. It is important to be precise about what this trial actually tested: both study arms were treatment-naive to the respective GLP-1 medicine at baseline — participants were not switched mid-study from one drug to the other. The trial therefore informs relative efficacy between the two molecules when started fresh, but does not directly answer the separate clinical question of what happens when someone who has already been on semaglutide is transitioned to tirzepatide partway through treatment.

Do I need a washout period between GLP-1 medicines?

There is no single, universally published protocol specifying a mandatory washout period when switching between semaglutide and tirzepatide, and clinical practice on this point varies between prescribers and services. Both molecules have long elimination half-lives — tirzepatide's is approximately five days, and semaglutide's is approximately one week — meaning that under some switching approaches, residual drug from the first medicine could still be present in the body when the second is introduced. Whether a formal washout interval, a direct transition, or an overlapping approach is used is a prescribing decision based on individual factors, not something this page specifies.

Can I switch on the NHS?

Switching within NHS pathways is not automatic. It depends on continued eligibility under the relevant NICE technology appraisal — TA875 for semaglutide, TA1026 for tirzepatide — and on the commissioning and clinical-review processes of the Integrated Care System or specialist weight management service managing care. See Mounjaro vs Wegovy — NHS access for the detailed eligibility comparison. A switch initiated for reasons of personal preference alone, without a clinical indication such as poor response or intolerance, may not be supported within NHS commissioning frameworks in the same way it might be in a private prescribing context.

What about tolerability when switching?

Semaglutide and tirzepatide share substantial mechanistic overlap through GLP-1 receptor signalling, which underlies much of the shared gastrointestinal tolerability profile across the class. Tirzepatide additionally engages the GIP receptor, which may contribute to differences some individuals report in appetite suppression or GI symptom pattern, though head-to-head tolerability comparisons specifically in people who have switched between the two — rather than treatment-naive comparisons — are limited in the published literature. Individual tolerability experience varies and prior intolerance to one molecule does not reliably predict tolerability to the other.

Should I titrate up from the start dose again?

Dose titration on switching is a specific clinical protocol decision that depends on factors including the dose reached on the previous medicine, time elapsed since the last dose, and individual tolerability history. This page does not provide dosing instructions or titration schedules — this is precisely the kind of decision that requires direct prescriber involvement, informed by product labelling and individual clinical context.

What should I discuss with my prescriber before switching?

Relevant discussion points typically include: the specific reason for considering a switch (plateau, tolerability, access, cost), review of current dose and response, any history of adverse effects on the current medicine, NHS eligibility status if relevant, and how titration and monitoring will be handled during the transition. This page provides background context for that conversation — it is not a substitute for it.

Frequently asked questions

Why do people switch from Wegovy to Mounjaro?

Reasons cited in clinical practice and patient forums include a plateau in weight loss on the current medicine, tolerability issues prompting a change of molecule, supply constraints affecting a specific product, or a clinician recommending a switch based on the comparative trial evidence. Any switch is an individual prescribing decision, not something this page recommends generally.

What does SURMOUNT-5 tell us about switching?

SURMOUNT-5 was a head-to-head trial comparing tirzepatide against semaglutide 2.4 mg in people who had not previously been on either medicine — it compared outcomes between two treatment-naive groups, not outcomes in people switching mid-treatment from one to the other. It is informative about relative efficacy between the molecules but does not directly answer what happens clinically when someone switches partway through treatment.

Do I need a washout period between GLP-1 medicines?

There is no standardised, universally published washout protocol for switching between GLP-1 receptor agonists, and clinical practice varies. Because both semaglutide and tirzepatide have long elimination half-lives (each in the region of five days for tirzepatide and about one week for semaglutide), residual drug from the first medicine may still be present when a second is started under some switching approaches. Whether and how a washout is applied is a prescribing decision.

Can I switch on the NHS?

Switching within NHS pathways depends on the individual's continued eligibility under NICE criteria (TA875 for semaglutide, TA1026 for tirzepatide) and the commissioning arrangements of the relevant Integrated Care System or specialist weight management service. It is not an automatic or guaranteed option and requires clinical review through the prescribing service.

What about tolerability when switching?

Switching between molecules does not necessarily reset gastrointestinal tolerability to a blank slate — both medicines share overlapping GI mechanisms via GLP-1 receptor activation, though tirzepatide additionally engages the GIP receptor. Some people report different tolerability profiles between the two; published head-to-head tolerability data specifically in switchers, as opposed to treatment-naive populations, remain limited.

Should I titrate up from the start dose again?

This is a specific prescribing question about dose titration protocol when switching, which depends on individual factors including prior dose, time since last dose, and tolerability history. This page does not provide dosing instructions — titration decisions when switching are made by the prescriber managing the change.

Is tirzepatide always more effective than semaglutide?

SURMOUNT-5 reported a greater mean percentage body-weight reduction with tirzepatide compared with semaglutide 2.4 mg at the population level over 72 weeks, but population-level averages do not predict individual response. Some people respond better to semaglutide than to tirzepatide, and trial-level superiority does not guarantee a better outcome for any specific individual considering a switch.

Does switching reset the NICE 104-week or 52-week review clock?

How a switch interacts with NICE-defined review timelines (104 weeks for TA875, periodic review for TA1026) is a commissioning and clinical-governance question that may vary between Integrated Care Systems and specialist services. This page does not provide a definitive national answer — check with the specific NHS service managing your care.

Can cost be a legitimate reason to switch?

For people accessing these medicines privately, relative cost between products is a practical consideration that many people weigh alongside clinical factors. This page does not comment on specific pricing, which varies by provider and over time, and cost alone does not override the clinical assessment a prescriber will make before agreeing to a switch.