Mounjaro vs Wegovy side effects: how do they compare?

Do Mounjaro and Wegovy cause the same side effects?

In short: mostly yes, with some nuance in severity and in one specific area. Both medicines share a GI-led side-effect profile. Nausea is the most commonly reported symptom on both, followed by vomiting, diarrhoea, constipation, indigestion and burping. The NHS tirzepatide page and the equivalent NHS semaglutide page both list these reactions as common, and both note that they tend to be most noticeable in the first few weeks or after a dose increase.

Where things get more nuanced: the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, directly compared tirzepatide (Mounjaro) against semaglutide 2.4mg (Wegovy) in adults with obesity. Rates of GI side effects were broadly similar between arms, with no dramatic difference in discontinuation due to tolerability. The short version is that neither medicine has a markedly cleaner gut profile than the other at their standard doses.

One area where guidance does differ is contraception. The NHS England weight-management-injections guidance notes that women taking Mounjaro who use the oral contraceptive pill should add a barrier method for the first four weeks of treatment and for four weeks after each dose increase, because Mounjaro's effect on gastric emptying may reduce pill absorption. There is no equivalent recommendation for Wegovy. Worth checking with your prescriber before you start either medicine if this applies to you.

Which medicine tends to cause more nausea?

This is the question our prescribers hear most weeks, and the honest answer is that individual variation outweighs population-level statistics. Some people sail through four weeks at the Mounjaro starter dose without any nausea at all. Others find the first weeks with Wegovy genuinely difficult. What both trials show is that the GI symptoms follow a predictable pattern: they peak at or just after initiation or a dose step, then ease.

The dose-titration schedule on both medicines exists precisely to manage this. Treatment starts low, allowing your system to adjust before moving up. The slower you climb, the more time your gut has to settle, and your prescriber will take that into account if you report persistent symptoms.

If nausea is your main concern, it helps to read about what Wegovy side effects typically involve and also to look at cases where people experience few or no side effects on Wegovy, since these do exist. The data suggest the absolute majority of GI symptoms resolve rather than persist.

Are there any side effects that appear with one medicine but not the other?

Both medicines carry the same serious but rare risks that come with all GLP-1 class treatments: pancreatitis, gallbladder problems and, in people with diabetes, hypoglycaemia if combined with certain other medicines. In January 2026 the MHRA issued a Drug Safety Update specifically highlighting pancreatitis as a known, infrequent but potentially serious risk across GLP-1 medicines. The symptom to watch for is severe, persistent stomach pain that may spread toward the back, sometimes with vomiting; this needs urgent medical attention, not a wait-and-see approach.

The comparison table below summarises key differences factually. One practical difference that does not appear in the table: Mounjaro is a dual GIP and GLP-1 agonist, which means its appetite-suppression pathway is somewhat distinct from Wegovy's. Some people who switch from one to the other report a different side-effect experience, though clinical evidence for this is limited. If you have had a difficult time with one medicine, that history is exactly the kind of thing a prescriber at nume needs to know before recommending an alternative.

How do you choose between them if side effects are your main concern?

The comparison table gives you a framework, but it cannot give you an answer. Which medicine's side-effect profile is more manageable for you depends on things a table cannot hold: your medical history, other medicines you take, your digestion, whether you have a history of gallbladder problems, and what your prescriber finds when they review your consultation.

If you want to go deeper on specific symptoms, the five most commonly reported Wegovy side effects are covered in detail separately, as is guidance on managing sulphur burps, which both medicines can occasionally cause. For a broader view of how the treatments compare on cost as well as tolerability, the Wegovy cost page covers what a full private course typically involves.

Which medicine suits you is a clinical decision made with our prescribers, not a conclusion anyone should draw from a comparison article alone. A free consultation with nume is the right starting point: a GPhC-registered prescriber reviews your answers the same day and works through exactly this question with you.