Switching from 12.5mg Mounjaro to Wegovy: What Does the Dose Comparison Look Like?

Why don't the milligram numbers translate directly between tirzepatide and semaglutide?

Mounjaro (tirzepatide) and Wegovy (semaglutide) are measured in milligrams, but the numbers aren't comparable across the two. Tirzepatide activates both the GIP and GLP-1 receptors simultaneously, while semaglutide targets the GLP-1 receptor alone. Because the underlying pharmacology differs, 12.5mg of tirzepatide produces a different physiological effect from any given dose of semaglutide, the molecules aren't interchangeable on a weight-for-weight basis.

Our prescribers are asked about this most weeks, usually by people mid-treatment who've had a supply disruption or who want to understand their options. The honest answer is that a prescriber considers where you are in your treatment journey, how you're tolerating your current dose, and which maintenance dose of Wegovy would be appropriate to start with, not a conversion table.

You can explore the broader framework for this kind of switch on our Mounjaro to Wegovy dose conversion page, which covers the general principles a prescriber applies.

Where does 12.5mg Mounjaro sit relative to Wegovy's maintenance doses?

At 12.5mg, you're on the second-highest dose in tirzepatide's six-step schedule, and the clinical evidence at this level is strong. In the SURMOUNT-1 trial, participants saw significant average weight reduction across the higher dose tiers; those on the 15mg ceiling achieved around 20–21% average body-weight loss over 72 weeks, as published in the New England Journal of Medicine. The 12.5mg tier sits just below that peak.

Wegovy's standard maintenance dose is 2.4mg weekly. A higher 7.2mg dose (supplied as a dedicated single-dose pen) was approved by the MHRA in April 2026 and produced around 20.7% average weight loss in trials, narrowing the gap with tirzepatide's top doses considerably. In the SURMOUNT-5 head-to-head trial, tirzepatide produced greater average weight reduction than semaglutide 2.4mg in adults with obesity, as noted in NICE's appraisal of tirzepatide (TA1026). That comparison shifts when the 7.2mg semaglutide dose enters the picture.

The table below summarises the key structural differences. Numbers are drawn from published trial data and regulatory sources.

For a side-by-side look at both medicines more broadly, our Wegovy vs Mounjaro page covers mechanism, eligibility and evidence in full.

What would actually happen to your dose if you switched?

Switching from a higher tirzepatide dose to semaglutide generally means starting at a lower semaglutide dose and titrating up, even if you've been stable on Mounjaro for months. This isn't because the prescriber doubts your tolerance, it's because the two medicines behave differently in the body and the cautious approach reduces the risk of unnecessary side effects during the transition. GI effects such as nausea, changes in appetite and digestive discomfort are common to both medicines, and a stepwise re-introduction manages that risk. Detailed guidance on the individual steps of a switch from the other direction is covered in our Wegovy to Mounjaro switching page.

People switching at lower tirzepatide doses face slightly different starting-point decisions; our page on moving from 7.5mg Mounjaro to Wegovy covers that scenario. For someone at 12.5mg who's been getting good results, a prescriber will also want to understand why you're switching (supply issues, side-effect profile, cost, or preference) because that context shapes what's recommended. If you're specifically looking at how that transition works from this dose, our guide to switching from Mounjaro 12.5mg to Wegovy walks through what that process typically involves.

Both medicines are prescription-only under UK law, and the NHS tirzepatide information page is a reliable starting point for understanding what the clinical picture involves. A prescriber at nume reviews every switch request individually; nothing is automated.

Which medicine is right for you at this stage of treatment?

There's no universally correct answer, and the framing of the question matters. If Mounjaro has been working well and supply is the issue, maintaining tirzepatide at a comparable dose is usually preferable to switching. If you're interested in moving to an oral option, the newly approved Wegovy tablet (25mg maintenance, licensed in the UK from June 2026) is a separate consideration worth raising with a prescriber. Cost context is relevant too, see our price comparison of Wegovy and Mounjaro for a factual overview of what private treatment typically costs.

Some people at this stage in treatment are also approaching the question from the perspective of what's available on the NHS. Tirzepatide is recommended by NICE under TA1026 for eligible adults, and Wegovy under TA875 with additional conditions including use within a specialist weight management service for a maximum of two years. Private treatment through a regulated pharmacy like nume is the alternative for those who don't meet NHS criteria or prefer not to wait. You can read more about our approach on our about us page or explore the full range of options on our weight loss treatment overview.

Which medicine suits you is a clinical decision our prescribers make with you, based on your history, your goals and the evidence. Check your eligibility and a GPhC-registered prescriber will review your consultation the same day.