Wegovy or Mounjaro — which has fewer side effects?

Do Wegovy and Mounjaro cause the same types of side effects?

Largely, yes. Nausea is the most commonly reported reaction with both medicines, followed by diarrhoea, constipation, vomiting, indigestion and fatigue. This is expected: both work by slowing gastric emptying and acting on appetite centres in the brain, so the gut feels the effect. The NHS patient information page for tirzepatide (Mounjaro) and its semaglutide equivalent list a nearly identical set of common reactions.

The pattern tends to be most noticeable in the first few weeks after starting or after a dose increase. For most people it settles. A question our prescribers hear most weeks is whether switching from one to the other would reduce nausea, and if you are trying to work out what has less side effects, Wegovy or Mounjaro, the honest answer is that it might, but individual responses vary enough that there is no reliable rule.

For a fuller breakdown of frequency comparisons, our detailed Wegovy vs Mounjaro side-effects page goes through the clinical-trial data reaction by reaction.

Where does the evidence point on which is better tolerated?

This is where the picture gets more nuanced. Mounjaro activates both GIP and GLP-1 receptors; Wegovy acts on GLP-1 alone. Whether that dual mechanism meaningfully changes tolerability in practice is not conclusively settled. SURMOUNT-1, the phase 3 trial for Mounjaro published in the New England Journal of Medicine, reported that gastrointestinal events were the most common reason for discontinuation, consistent with semaglutide trials. Neither trial was designed to compare tolerability head-to-head.

The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, did compare tirzepatide directly with semaglutide 2.4mg over 72 weeks. It was primarily a weight-loss efficacy trial; the safety and tolerability data showed broadly similar gastrointestinal adverse-event profiles across both arms, without a statistically clear winner on tolerability. Whether side effects are worse on one or the other therefore cannot be answered with a single figure.

The table below summarises what the evidence and UK labelling show:

Source: NHS tirzepatide; NHS semaglutide; MHRA Drug Safety Update, January 2026.

Are there any safety differences that actually matter day-to-day?

One practical difference stands out. For women taking the oral contraceptive pill, Mounjaro's slowing effect on gastric emptying may reduce how much of the pill is absorbed. UK guidance recommends adding a barrier method for the first four weeks of Mounjaro treatment and for four weeks after each dose increase. Semaglutide (Wegovy) does not carry the same specific instruction, though any significant GI illness on either medicine can theoretically affect pill absorption, so the conversation with your prescriber is worth having either way.

Both medicines carry the January 2026 MHRA pancreatitis signal: get urgent medical help for severe, persistent abdominal pain that radiates to the back, particularly with vomiting. This applies equally to both. Gallbladder issues, dehydration from prolonged vomiting, and injection-site reactions are also shared. Which has more side effects overall depends significantly on dose and the individual.

Ozempic and Rybelsus are also semaglutide, but they are licensed for type 2 diabetes, not weight management. They are not interchangeable with Wegovy for this purpose, and a prescription for weight loss on those brands would not be appropriate under UK licensing. Our full Wegovy vs Mounjaro comparison covers cost, availability and efficacy alongside the tolerability picture.

So which should you choose if tolerability is your main concern?

Tolerability alone is rarely the deciding factor in isolation. Your medical history, any medicines you already take, your BMI and the presence of weight-related conditions all shape which medicine a prescriber would consider first. If you have had a poor experience with one GLP-1 medicine in the past, that history is relevant, and worth raising in detail.

Neither medicine is clearly the gentler option based on current evidence. What does differ is the dual-receptor mechanism of Mounjaro, the contraceptive-interaction point noted above, and the fact that Mounjaro has consistently shown greater average weight loss in trials, which may make a difference if efficacy is being weighed alongside tolerability. Readers weighing up which has fewer side effects should also factor in that titration pace matters: slower increases give the gut more time to adjust.

Which suits you is a clinical decision our prescribers make with you, based on your full picture. Start your free consultation and a GPhC-registered Independent Prescriber will review your answers the same day.