Switching from Mounjaro to Retatrutide: What the Dosage Difference Means for You

Is retatrutide actually available to switch to in the UK?

This is the question that tends to get lost in the enthusiasm around retatrutide's early trial numbers. As of summer 2026, retatrutide has no UK marketing authorisation for any indication. It is a triple receptor agonist (acting on GIP, GLP-1 and glucagon receptors simultaneously) and phase 3 trials are ongoing, but it has not been approved by the MHRA for weight management or any other condition. Mounjaro, by contrast, received its UK licence for weight management in adults, and NICE issued its recommendation (TA1026) in December 2024. The licensed dosage schedule for Mounjaro runs from a 2.5mg starting pen through 5, 7.5, 10, 12.5 and up to 15mg, titrated roughly every four weeks under prescriber guidance. That regulatory track record is what makes it prescribable today. Retatrutide has no equivalent framework yet. Anyone offering to switch you onto retatrutide through a UK pharmacy, at any dose, should be viewed with serious scepticism, the MHRA has warned repeatedly about unlicensed medicines sold online, and suspected illegal sellers can be reported via the Yellow Card scheme. A switching decision from tirzepatide to retatrutide dosage simply cannot be made responsibly at this point in the UK, however promising the pipeline looks.

How do the dosage ranges compare on paper?

Comparing dosage numbers across these two medicines is genuinely instructive, even if a direct clinical switch isn't possible yet. Mounjaro's titration ladder is well established: the 2.5mg pen is a tolerability step that lets the body settle, and therapeutic effect builds as the dose climbs. The full schedule, including what each pen delivers in volume terms, is covered in detail on the Mounjaro dosage guide. Retatrutide, based on published phase 2 data, was studied at doses up to 12mg weekly in the weight management programme, with the highest dose arm producing striking average weight reductions. In one phase 2 trial, participants at 12mg lost around 24% of body weight over 48 weeks, a figure that generated considerable attention. The caveat is that phase 2 trials are smaller and shorter than phase 3; they don't yet confirm the full safety and efficacy profile that licensing bodies require. Mounjaro's own evidence base spans thousands of participants across the SURMOUNT programme, including SURMOUNT-1, which was published in the New England Journal of Medicine. For a side-by-side look at how the titration schedules differ structurally, the retatrutide versus Mounjaro dosage comparison sets them out in full context.

A common misconception worth setting down gently: higher trial numbers don't automatically mean a medicine is better for a given individual. Phase 2 results often look more dramatic than phase 3 data, and the patient populations, trial lengths and endpoints differ. The comparison is interesting, not conclusive.

What should someone currently on Mounjaro actually consider?

For most people on Mounjaro right now, the more immediate and actionable question is whether they're at the right dose, or whether there's more progress to be made within the licensed schedule. Reaching 15mg and asking what comes next is a real concern, and it's one our prescribers think about carefully with each person. The guide to what happens at Mounjaro's highest dose covers the clinical considerations in detail. Switching from tirzepatide to retatrutide dosage isn't a live clinical option; exploring whether the existing titration schedule has been fully optimised usually is. That might mean reviewing whether side effects limited earlier dose increases, whether lifestyle factors have shifted, or whether an alternative licensed medicine such as Wegovy might suit better. Our Mounjaro overview sets out the full eligibility and process picture for people considering starting or continuing treatment. If cost is part of the calculation, the honest guide to Mounjaro pricing in the UK explains what private treatment actually involves. Which option suits your specific situation is a clinical decision, and one our prescribers work through with you directly, not something a dosage chart can settle alone.

When might switching to retatrutide become a real conversation?

Realistically, if retatrutide completes phase 3 trials with a favourable outcome and the MHRA grants a UK licence, a switching conversation would follow the same clinical pathway as any other medicine change: a full prescriber review, evidence of current treatment, and a titration plan set by the clinician. The dosage at which someone might start retatrutide after stopping tirzepatide would not simply mirror their Mounjaro dose, the receptor profile is different, the formulation is different, and the body's response needs to be assessed from scratch. The retatrutide versus tirzepatide dosage chart maps out the structural differences for readers who want to follow the evidence as it develops. NICE guidance, as seen in its appraisal of tirzepatide (TA1026), requires a full evidence review before recommending any medicine, and that process takes time after licensing. The honest position for anyone curious about retatrutide is to stay informed, remain on a well-managed current treatment, and speak to a prescriber when the regulatory picture changes. In the meantime, starting a free consultation is the right first step for anyone whose current treatment needs reviewing.