Mounjaro®
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Start journey Learn moreHow the two medicines compare, and what the evidence says about switching at this dose
You're nearly at the top of the semaglutide schedule, here's what that means for a switch
Picture this: you've been titrating steadily, you're now on the 1.7mg Wegovy dose, and progress has started to plateau. Or perhaps your next scheduled step to 2.4mg feels uncertain. Either way, the question of switching to tirzepatide (Mounjaro) comes up, and it's worth understanding why the two drugs don't map onto each other neatly before you ask your prescriber.
Semaglutide is a GLP-1 receptor agonist, it activates one gut-hormone pathway involved in appetite regulation and gastric emptying. Tirzepatide activates two: GIP as well as GLP-1, making it the only dual-agonist weight-loss medicine licensed in the UK. That additional receptor activity is part of why the clinical trial results differ. It also means tolerability profiles, titration schedules and dose equivalences don't translate across directly. The question of semaglutide-equivalent dosing has no single published answer, prescribers use clinical judgement guided by your current dose, how long you've been on it, and how well you've tolerated it.
One practical habit worth building before any consultation: check the batch number on your current pen against the MHRA's product verification guidance. It takes under a minute and confirms you're working from a genuine, licensed supply, important context if you're considering a switch and want to account for what you've actually been receiving.
At 1.7mg you're in the upper range of the weekly injection schedule, and our guide to moving from 1mg semaglutide to tirzepatide explains what that trajectory typically looks like when a switch is being considered. That context matters when a prescriber is deciding whether to complete the course to 2.4mg first, or whether switching now makes clinical sense for you specifically.
What the trial evidence shows, and how tirzepatide's results compare at full dose
In SURMOUNT-1, published in the New England Journal of Medicine, adults with obesity taking tirzepatide at its highest dose (15mg) lost around 20–21% of body weight over 72 weeks on average. In the STEP 1 trial, semaglutide 2.4mg produced roughly 15% average reduction over 68 weeks. Both figures are trial averages in controlled populations, individual outcomes differ, and neither number is a guarantee.
The SURMOUNT-5 trial, also published in the New England Journal of Medicine (2025), compared tirzepatide directly against semaglutide 2.4mg in a head-to-head open-label study involving 751 adults with obesity and no diabetes over 72 weeks. Tirzepatide produced greater average weight reduction. The gap narrows with the newer 7.2mg semaglutide dose now approved by the MHRA, but the broader evidence base still favours tirzepatide at equivalent points in the titration journey. NICE referenced this indirect comparison in its appraisal of tirzepatide (TA1026).
What those numbers don't tell you is how someone on 1.7mg semaglutide specifically performs if they switch mid-schedule to tirzepatide's starter dose. There's no published conversion table for that scenario, which is exactly why a prescriber-led dosage review for switching matters more than any rule of thumb you'll find online.
A side-by-side look at the two medicines at this point in treatment
| Factor | Semaglutide 1.7mg (Wegovy) | Tirzepatide (Mounjaro) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP + GLP-1 receptor agonist |
| UK weight-loss licence | Yes (Wegovy injection) | Yes (Mounjaro) |
| Position in schedule | Penultimate step before 2.4mg maintenance | Mid-titration (out of 2.5–15mg range); 1.7mg has no direct equivalent |
| Average weight loss (full dose, trial data) | ~15% at 2.4mg (STEP 1, NEJM) | ~20–21% at 15mg (SURMOUNT-1, NEJM) |
| Side-effect profile | GI-led: nausea, diarrhoea, constipation, reflux | GI-led: similar profile; dual-agonist mechanism may affect tolerability differently |
| Prescriber-led dose conversion needed? | N/A (you're already on it) | Yes, no standard published conversion from 1.7mg semaglutide |
Figures from SURMOUNT-1 (NEJM) and STEP 1 (NEJM); SURMOUNT-5 head-to-head (NEJM, 2025); NICE TA1026. Individual results vary. Both medicines are prescription-only and require clinical assessment.
How a switch would actually work, and what happens at your consultation
If you're already on semaglutide and want to explore tirzepatide, the process starts with a consultation, not a form that approves you automatically. At nume, a GPhC-registered Independent Prescriber reads your answers the same day, they'll want to know your current dose and how long you've been at it, your weight trajectory, any side effects you've experienced, and your medical background. Transfer patients are asked to provide evidence of their current treatment; that's standard clinical practice, not bureaucracy.
A prescriber considering a switch from 1.7mg semaglutide would typically look at whether you've had the chance to reach 2.4mg first, since completing the licensed course has its own evidence base. If a switch is appropriate, tirzepatide almost always starts at 2.5mg, that dose exists to let your system adjust, not to deliver the full therapeutic effect immediately. The semaglutide-to-tirzepatide dose conversion question has no off-the-shelf answer, and anyone presenting one as a simple ratio should be approached with caution.
Which medicine suits you at this point in your journey is a clinical decision, one our prescribers make with you, taking your full history into account. You can read more about the broader comparison on our Wegovy vs Mounjaro page, or explore all available treatment options if you're earlier in your decision. When you're ready, start your free consultation and a prescriber will review your case the same day.
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