FAQ · GLP-1 · Editorial commentary

What does the published guidance say about switching between Wegovy and Mounjaro?

Editorial commentary on the published Summaries of Product Characteristics and UK prescribing practice. Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are UK prescription-only medicines licensed for weight management within their respective MHRA-approved indications. A switch between the two is a clinical decision made between a patient and their UK-licensed prescriber. The published SmPCs for each medication set out the licensed titration schedules and starting doses. PeptideClear does not publish switching protocols because the appropriate washout period, restart dose, and titration cadence depend on the individual patient and are set by the prescriber managing the switch.

A switch between Wegovy and Mounjaro is a clinical decision between you and your UK-licensed prescriber. The correct washout window, restart dose, and titration plan are set by the prescriber managing your case. The notes below are editorial commentary on the published pharmacology and guidance, not switching instructions.

What the published pharmacology describes

Published pharmacology reports that semaglutide has a half-life of approximately seven days and tirzepatide has a half-life of approximately five days. Both medications are administered as once-weekly subcutaneous injections. The two molecules are not bioequivalent: semaglutide is a GLP-1 receptor agonist, tirzepatide is a dual GIP and GLP-1 receptor agonist. Response to one does not predict response to the other.

What the SmPCs report on starting doses

The MHRA-approved SmPC for each medication sets out a starting dose and a titration schedule, with the published rationale that low starting doses and stepwise titration support tolerability of the gastrointestinal effects of GLP-1 receptor agonism. The published licensed titration ladders are the same regardless of whether the patient is new to GLP-1 medications or coming from a different GLP-1 product, unless the prescriber documents a clinical reason to vary. The detail is set out in the SmPC published on emc.medicines.org.uk.

Why a washout window is discussed in prescribing practice

Editorial note. In UK prescribing practice, prescribers commonly leave a washout period between the last dose of one weekly GLP-1 and the first dose of another, to avoid overlapping peak plasma concentrations. The specific length of any washout is a clinical decision based on the individual case, the prior dose, tolerability history, and prescriber judgement. PeptideClear does not publish a specific number because the right answer depends on the individual and is set by the prescriber.

Why patients discuss switching with their prescriber

Common reasons reported in published clinical commentary include weight loss plateau on the current medication at maximum tolerated dose, tolerability issues that may be specific to the molecule rather than the class, cost considerations, and preference for a medication with a different licensed indication (for example a cardiovascular outcomes indication). The decision is individual and clinical.

Where to ask

· Your prescriber. NHS GP, NHS Specialist Weight Management Service, private clinic prescriber, or pharmacist prescriber.
· The published SmPCs and PILs for each medication on emc.medicines.org.uk.
· Adverse effects associated with either medication can be reported via MHRA Yellow Card.

Decision routing: switching is a clinical decision. Your UK-licensed prescriber sets the washout, restart dose, and titration cadence. This page is editorial commentary, not switching instructions.