Mounjaro or Wegovy: which has more side effects?

You've been comparing the two and every list looks almost identical, so where do they actually differ?

That frustration is reasonable. Mounjaro and Wegovy share so much of their side-effect territory that the lists feel interchangeable at first glance. Both are once-weekly injections; both slow gastric emptying; both suppress appetite through gut-hormone pathways. The overlapping consequences are nausea, vomiting, diarrhoea, constipation, reflux, burping, fatigue and headache, all driven by the medicines' shared effect on the digestive system. A fuller breakdown of how the profiles sit side by side helps make sense of the nuance.

The key mechanical difference: tirzepatide activates two receptors (GIP and GLP-1), while semaglutide targets one (GLP-1 only). Whether that dual action translates into a meaningfully different side-effect burden in practice is not settled, because trial populations, reporting methods and dose escalation speeds all influence what gets counted, making direct percentage comparisons unreliable across separate studies. The honest answer is that individual tolerance varies considerably, some people find Mounjaro gentler; others have a worse time on it than they did on semaglutide.

One practical difference is worth flagging. Because tirzepatide can reduce absorption of oral medicines during the early weeks of treatment, women taking oral contraceptives are advised to add a non-oral method for the first four weeks of treatment and for four weeks after each dose increase. NHS guidance does not carry an equivalent recommendation for semaglutide. That is not a side effect in the traditional sense, but it is a clinically important distinction, and if you are weighing up which medicine tends to produce fewer effects overall, this and other practical considerations are worth reading through.

What the clinical trial data actually shows

The SURMOUNT-1 trial, published in the New England Journal of Medicine, reported that gastrointestinal events were the most common adverse effects with tirzepatide, with rates broadly consistent with other GLP-1 class medicines. Nausea and diarrhoea were most frequent at the point of each dose step, generally settling within days to around two weeks. The STEP 1 trial for semaglutide 2.4mg versus Mounjaro, also in the New England Journal of Medicine, showed a similar pattern, GI events peaking at initiation and dose escalation, with comparable tolerability profiles at maintenance doses.

The SURMOUNT-5 head-to-head trial (72 weeks, 751 adults with obesity and no diabetes, published in the New England Journal of Medicine in 2025) compared tirzepatide directly with semaglutide 2.4mg. It was powered to assess weight loss, not side effects as a primary endpoint, so it does not give us a definitive answer on tolerability. What it does show is that both medicines were used to completion by a substantial proportion of participants, suggesting neither is dramatically harder to tolerate than the other at a population level.

The table below summarises the key points of comparison using trial-reported data and licensed-prescribing information.

The one safety signal that applies to both, and when to call for help

In January 2026, the MHRA issued a Drug Safety Update covering GLP-1 medicines as a class, specifically highlighting acute pancreatitis. It is infrequent, but it can be serious. The symptom to act on is severe, persistent stomach pain that spreads to the back, with or without vomiting, that warrants urgent medical attention, not waiting to see whether it settles. You can read the full safety communication and report any suspected side effect via the MHRA Yellow Card scheme.

Other signs that need prompt attention on either medicine: symptoms of gallbladder problems (sudden pain under the right ribcage), signs of dehydration from severe vomiting or diarrhoea, and allergic reactions such as facial swelling or breathing difficulty. Low mood or thoughts of self-harm are also listed in the prescribing information for both medicines, tell your prescriber if your mental health changes after starting treatment.

The good news is that most people do not experience these serious effects. The side effects most people actually encounter are the GI ones at the beginning, and there are practical strategies for managing them. Eating slowly, choosing smaller meals, avoiding very fatty or rich food during dose escalation and staying well hydrated all help. Your prescriber can advise further, and at nume, that advice is part of the aftercare, not an add-on.

Which medicine is right for you, and what choosing through a regulated service actually looks like

The short answer is that neither Mounjaro nor Wegovy has a definitively worse side-effect burden. Individual biology, other medicines, medical history and tolerance all shape your actual experience. Which suits you is a clinical decision our prescribers make with you, not something a comparison table can resolve.

If you start treatment through nume, a named GPhC-registered Independent Prescriber reviews your consultation before any prescription is issued. There is no algorithm in that step. If you are approved, your treatment arrives the next working day in a plain DPD parcel, tracking link on your phone, no branding on the box. Every repeat order is clinically re-reviewed, so a prescriber sees you at each stage of dose escalation, not just at the start.

You can read more about how our clinical team is structured, or see our lead prescriber's profile if you want to know who is reviewing consultations. For questions that do not fit neatly into a comparison page, our FAQs cover the most common ones. When you are ready, speak to our prescribers through a free consultation, the clinical picture is what decides this, not the headline numbers.