Wegovy or Mounjaro: which is safer for you?

Same regulator, similar warnings — but one specific difference worth knowing

Both medicines are authorised by the MHRA, carry a Black Triangle (▼) status requiring additional monitoring, and share a broadly similar list of risks. The most common side effects for both are gastrointestinal: nausea, diarrhoea, vomiting, constipation, and reflux tend to be most noticeable when starting or stepping up a dose, and usually settle over days to a couple of weeks. Serious but less common risks (including acute pancreatitis, gallbladder problems, and allergic reactions) apply to both, and the MHRA's Yellow Card scheme monitors both actively.

The one clinically documented distinction concerns oral contraceptives. For tirzepatide (Mounjaro), because the medicine slows gastric emptying, the MHRA advises adding a non-oral method of contraception (condoms, for instance) during the first four weeks of treatment and for four weeks after each dose increase, since pill absorption may be reduced. No equivalent evidence exists for semaglutide. If you take the pill, that is a concrete factor your prescriber will factor in when deciding which medicine suits you. It does not make Mounjaro less safe overall; it is a management step, not a contraindication.

Both medicines are not recommended during pregnancy, while breastfeeding, or when actively trying to conceive. Neither is licensed for anyone under 18. History of medullary thyroid carcinoma or MEN2 syndrome requires careful prescriber discussion before either is started. The NHS medicines page for tirzepatide and the equivalent for semaglutide both carry full contraindication lists worth reading before your consultation.

What the head-to-head trial tells us, and what it doesn't

SURMOUNT-5, published in the New England Journal of Medicine in 2025, was a 72-week open-label trial in 751 adults with obesity but without diabetes. It compared tirzepatide directly against semaglutide 2.4mg, the first head-to-head study of this kind. On average, participants taking tirzepatide lost more body weight than those on semaglutide. The weight-loss difference between the two was meaningful, though both produced significant results. NICE's appraisal of tirzepatide (TA1026) also notes that indirect comparisons favour tirzepatide on weight loss endpoints.

Crucially, SURMOUNT-5 was designed around efficacy, not a head-to-head safety comparison. Both medicines showed tolerability profiles consistent with their earlier trials. Discontinuation due to side effects was low in both groups. So the trial strengthens confidence in both treatments, but it does not establish that one is pharmacologically safer than the other.

The arrival of Wegovy at a 7.2mg maintenance dose (the dedicated single-dose pen was approved by the MHRA in April 2026) narrows the average weight-loss gap further for some patients. Whether that higher dose suits you individually is a clinical question, not a marketing one. Our clinical team reviews each case on its own terms.

Individual history is what the safety question is really about

Ask a prescriber whether Mounjaro or Wegovy is safer, and their honest answer will begin with questions, not assertions. Your kidney function, any history of pancreatitis or gallstones, whether you have type 2 diabetes, your cardiovascular status, your current medicines, all of these shape which option is the more appropriate starting point and which titration schedule makes sense.

Some people find one medicine produces more nausea than the other at the same relative dose step; that is individual variation, not a population-level safety signal. Dose titration (moving up slowly, in four-week steps) is the primary tool for managing tolerability on both. A prescriber who knows you can pace that correctly.

The comparison below sets out the key factual differences. The numbers are drawn from the published trial data and NICE guidance; they describe populations, not predictions for any single person. For a more detailed look at how the two medicines compare on safety specifically, the safety comparison between Wegovy and Mounjaro covers what the evidence currently shows. For a cost-focused view, the UK price comparison covers what each treatment typically costs privately.

How to reach a decision you can act on

The practical question is not which medicine wins a safety ranking, but which one a prescriber considers right for your situation today. At nume, a GPhC-registered Independent Prescriber reads your answers (including your medical history, medicines list, and weight verified on a live video call) before any treatment is approved. That review happens the same day. If you place an order before 12pm on a weekday and your prescription is approved, your treatment leaves our pharmacy that afternoon and arrives with you the next working day.

If you want to explore how the two options compare more broadly before your consultation, the full Wegovy vs Mounjaro overview covers efficacy, eligibility, and what to expect. You can also read about which tends to produce better results and why the answer is more nuanced than a single trial figure. Which suits you is a clinical decision our prescribers make with you.