Wegovy Side Effects Compared to Mounjaro: What the Evidence Shows

Do Wegovy and Mounjaro cause the same side effects?

Largely, yes. Nausea is the most commonly reported complaint with both medicines, followed by loose stools or constipation, indigestion, burping and fatigue. These symptoms cluster around the same biological cause: both drugs slow gastric emptying and suppress appetite through gut-hormone pathways, and the stomach takes time to adjust. In most people the discomfort is mild to moderate and settles within the first couple of weeks on a new dose.

Where the profiles start to diverge is in frequency and intensity. Because Mounjaro acts on both GIP and GLP-1 receptors, its effect on gastric emptying is generally stronger, which some people find means more noticeable nausea early on, particularly at the higher doses. Wegovy's single GLP-1 pathway tends to produce a somewhat gentler onset for many patients, though individual variation is wide. Neither is painlessly well-tolerated by everyone. You can read a more detailed breakdown of individual reactions on our Mounjaro and Wegovy side effects page.

Injection-site reactions (redness, mild stinging, occasional bruising) are possible with both, since both are given as once-weekly subcutaneous injections. Rotating your injection site each week reduces this. Headache and dizziness appear in the trial data for both medicines too, most often in the first month.

One practical note: the titration schedule exists precisely to manage tolerability. Starting at 2.5 mg for Mounjaro (or 0.25 mg for Wegovy), the dose rises gradually under a prescriber's guidance so your body acclimatises before reaching a therapeutic level. Rushing through that schedule is the commonest reason early side effects become difficult to manage.

Are there any side effects unique to one medicine?

There are differences worth knowing, even if none are absolute. The MHRA has flagged that women taking oral contraceptives should add a barrier method for the first four weeks of Mounjaro treatment and for four weeks after each dose increase, because tirzepatide's effect on gut transit can reduce pill absorption. The equivalent evidence for semaglutide (the active ingredient in Wegovy) does not point to the same concern. NHS guidance similarly recommends discussing transdermal HRT (patches or gels rather than tablets) if you are on tirzepatide, for the same absorption reason. These are not side effects in the conventional sense, but they are clinically meaningful interactions that the two medicines handle differently.

Pancreatitis is listed as an uncommon but serious risk for both. In January 2026 the MHRA issued a Drug Safety Update highlighting acute pancreatitis across GLP-1 medicines: severe stomach pain that spreads to the back, with or without vomiting, needs urgent medical attention and should not be put down to ordinary nausea. That warning covers tirzepatide and semaglutide alike.

Gallbladder problems, including gallstones, appear in the data for both medicines, linked to rapid weight loss rather than the drug itself. Dehydration from prolonged vomiting or diarrhoea can place strain on the kidneys, staying well hydrated matters, especially in the first weeks. Any side effect that feels severe or persistent should be reported to your prescriber. Suspected adverse reactions can also be logged with the MHRA's Yellow Card scheme.

For a closer look at whether one produces fewer complaints than the other, our page on which has fewer side effects, Mounjaro or Wegovy, works through the trial data in detail.

What does the head-to-head trial evidence tell us?

The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, was the first properly powered head-to-head comparison of tirzepatide (Mounjaro) and semaglutide 2.4 mg (Wegovy) in adults with obesity. It ran for 72 weeks across 751 participants. On weight loss, tirzepatide produced a meaningfully larger average reduction. On tolerability, discontinuation rates due to adverse events were comparable between the two arms, suggesting that although side effects were present in both groups, they did not cause materially more people to stop one medicine over the other.

That finding is consistent with the individual trial data. SURMOUNT-1 (tirzepatide, 72 weeks) and STEP 1 (semaglutide 2.4 mg, 68 weeks) both reported GI side effects as the primary complaint, with most events grading as mild or moderate. NICE's appraisal of tirzepatide (TA1026) and its earlier semaglutide recommendation (TA875) both accepted the trial safety data as satisfactory for recommendation.

The table below summarises the key side-effect differences based on UK regulatory and trial evidence.

If you'd like the broader efficacy picture alongside this safety comparison, our Wegovy vs Mounjaro overview covers results, eligibility and cost context together.

Which side-effect profile suits you, and how does a prescriber decide?

That's exactly the right question, and it doesn't have a single answer. Someone who already manages oral contraceptives or takes HRT tablets might find the tirzepatide interaction guidance means Wegovy is the more straightforward starting point. Someone who has tried Wegovy and found the nausea unmanageable may do better on a different titration schedule rather than a different medicine, or vice versa, and our guide to how Wegovy and Mounjaro compare on side effects can help you think through what to raise with your prescriber. Prior GI conditions, other medicines you take, and how your body responded to any previous GLP-1 treatment all factor in.

What a prescriber brings to this is a full clinical picture: your health history, your current medications, your weight trend and what you're hoping to achieve. That's why the process at nume includes a same-day review by a GPhC-registered Independent Prescriber, not a questionnaire that auto-approves. The aim isn't to match you to a product; it's to match you to the right clinical plan.

Both medicines are prescription-only and both require ongoing clinical oversight. If a side effect troubles you between doses, our aftercare team is available seven days a week. You can also find general answers to common questions on our FAQs page. For pricing context across both treatments, our Mounjaro and Wegovy price comparison page sets out what's included. Which medicine suits you is a clinical decision our prescribers make with you, and if you want to explore the full side-effect picture for Wegovy versus Mounjaro before starting that conversation, that detail is there when you need it. Start your free consultation and that conversation can begin today.