Mounjaro®
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Start journey Learn moreWhat the evidence and UK guidance say about switching GLP-1 medicines
The biggest myth: that you can just stop one and start the other
People often assume switching is straightforward — finish the pen you're on, start the new one. It's an understandable thought, and there's no malice in it. But both Wegovy and Mounjaro are pharmacologically active for longer than a single week, and jumping between them without a plan can mean stacking effects you didn't intend or running into side effects that are harder to manage. The washout period between Wegovy and Mounjaro depends on which direction you're moving, how long you've been on the current medicine, and what dose you're at, none of which a blanket rule can answer.
There's also a structural difference between the two medicines. Wegovy (semaglutide) is a GLP-1 receptor agonist. Mounjaro (tirzepatide) activates both GLP-1 and GIP receptors, the only dual-agonist weight-loss injection licensed in the UK. That distinction shapes how a prescriber plans a transition, not just whether one is "stronger" than the other.
Whether a break is needed at all is covered separately, and the answer is more nuanced than most posts on the topic suggest. Our page on whether you need a break between Wegovy and Mounjaro goes through the clinical logic in detail.
How switching actually works: dose, timing and what a prescriber weighs up
A prescriber considering a switch will look at several things: your current dose and how long you've been on it, your side-effect history, your weight trajectory, and whether the reason for switching is tolerability, plateau, availability, or clinical preference. None of those factors point to a universal rule.
Moving from Wegovy to Mounjaro typically means starting at Mounjaro's 2.5 mg dose, the starter dose exists to let your system adjust, regardless of what you were previously taking. That can feel counterintuitive if you were stable on 2.4 mg of semaglutide, but the receptor pathways differ enough that stepping down on introduction is standard clinical practice, per the Mounjaro Summary of Product Characteristics on the Electronic Medicines Compendium. Moving in the other direction, from Mounjaro to Wegovy, involves similar considerations, the switch from Mounjaro to Wegovy page covers the specifics.
The two medicines share a GI-led side-effect profile: nausea, loose stools, indigestion and fatigue are common at initiation and after dose increases, usually settling within days to a couple of weeks. A poorly timed switch can make those effects harder to attribute and harder to manage, which is one reason the transition needs clinical eyes on it.
Comparing Wegovy and Mounjaro: the numbers that matter
The headline trial figures are worth knowing, because they're the basis on which NICE recommended both medicines.
| Feature | Wegovy (semaglutide 2.4 mg) | Mounjaro (tirzepatide 15 mg) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP + GLP-1 receptor agonist |
| Average weight loss (trial) | ~15% over 68 weeks (STEP 1, NEJM) | ~20–21% over 72 weeks (SURMOUNT-1, NEJM) |
| Head-to-head evidence | SURMOUNT-5 (NEJM 2025): tirzepatide produced greater average weight reduction than semaglutide 2.4 mg over 72 weeks | |
| NICE recommendation | TA875 (max 2 years, specialist weight management service | TA1026) BMI ≥35 + ≥1 comorbidity (private licence is broader) |
| Frequency | Once weekly injection | Once weekly injection |
A fuller breakdown of how the two medicines sit side by side (mechanism, eligibility, cost context) is on our Wegovy v Mounjaro comparison page. Note that Ozempic, while also semaglutide, is licensed for type 2 diabetes rather than weight management and shouldn't be conflated with Wegovy; the same applies to Rybelsus, the oral semaglutide tablet licensed for diabetes, not weight loss.
Which medicine suits you, and who decides
There's a version of this question that's really asking: which is better? The SURMOUNT-5 trial gave the clearest head-to-head data to date, with tirzepatide ahead on average weight loss. But averages don't tell your story. Someone who tolerates semaglutide well, has been losing steadily for a year, and is two months from finishing their NICE-funded course has a very different picture from someone who plateaued at 7.5 mg of tirzepatide and is wondering whether a switch might help. Our clinical team, led by our prescribers, works through exactly that kind of question at consultation.
The comparison between the two medicines, including cost context, is worth reading before you reach a consultation, how Wegovy and Mounjaro compare on price is covered separately. And if you're already partway through a decision, how to choose between Wegovy and Mounjaro sets out the practical factors a prescriber considers. Which medicine suits you is a clinical decision our prescribers make with you, not one this page can make for you. Check your eligibility with a free consultation and a prescriber will review your case the same day.
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