Do Wegovy and Mounjaro cause different side effects — and does one cause more?

Picture this: you're trying to choose, and both information sheets look almost identical

You've read the Patient Information Leaflets for both medicines, and they both lead with nausea, then diarrhoea, then constipation, then vomiting, then indigestion. Understandably, you're none the wiser about whether one is likelier to leave you queasy than the other. That frustration is fair. The similarity isn't coincidence, both medicines slow gastric emptying and reduce appetite through overlapping pathways, so the gut reacts in overlapping ways.

The key difference is that Mounjaro activates both the GLP-1 and GIP receptors, while Wegovy targets GLP-1 alone. Some researchers expected the dual action to mean more GI disruption; the trial data didn't quite bear that out. In SURMOUNT-1, around 44% of participants on the highest tirzepatide dose reported nausea, with most cases mild-to-moderate and most settling within the first few weeks. Comparable semaglutide trial populations reported nausea rates in a similar range. The headline rates are close enough that neither medicine has a clear "worse" label backed by direct head-to-head safety data. You can read more about how the semaglutide and tirzepatide side-effect profiles compare at the molecular level if that helps frame the choice.

One practical note our prescribers raise often: side effects are most noticeable after starting a new dose, then typically ease. Both medicines titrate slowly for exactly this reason. The starter dose exists to settle your system before the therapeutic work begins.

Where the profiles do differ, and what that means in practice

Here is where the nuance lies. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, compared tirzepatide directly with semaglutide 2.4mg over 72 weeks. It was primarily designed to assess weight loss, not side effects, but its tolerability data adds useful context. Discontinuation due to adverse events was broadly comparable between the two groups, suggesting neither medicine is dramatically harder to stay on.

That said, some differences do emerge on closer reading. Constipation appears to be reported slightly more often with tirzepatide than with semaglutide across various trial populations. Injection-site reactions are possible with both. The Mounjaro versus Wegovy safety comparison covers this in more depth, including the specific contraindications that differ between the two.

One common misconception worth setting aside gently: that the medicine producing more weight loss must be producing more side effects to earn it. That's not how GLP-1 or dual-agonist medicines work. Greater efficacy in trials reflects the added GIP pathway activation, not a higher burden of symptoms.

There's also the question of oral versus injectable format. The newer Wegovy tablet (approved by the MHRA in June 2026 as the first oral GLP-1 medicine licensed in the UK for weight management) carries its own GI profile; around 74% of participants in its trial reported GI symptoms, which is higher than the injectable's rates, though most were mild and transient. That's a separate conversation from the Wegovy injection versus Mounjaro injection comparison, but worth flagging if needles are part of why you're researching.

Side-effect comparison at a glance

Both medicines carry a Black Triangle (▼) designation from the MHRA, meaning they are subject to additional monitoring. Suspected side effects from either can be reported at the MHRA Yellow Card scheme, something we actively encourage anyone on treatment to know about. The question of whether Wegovy causes fewer side effects than Mounjaro is one that keeps coming up in this comparison, and the honest answer remains: probably not in any clinically meaningful way across most people.

What this means when you're choosing, and how a prescriber fits into that

Your medical history matters here more than population averages. Someone with a history of reflux may find one medicine sits better; someone with existing constipation may want to factor in that tirzepatide data. These are exactly the conversations that happen during a clinical consultation, not a checklist a website can complete for you.

Both Wegovy and Mounjaro are licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 or above alongside a weight-related health condition. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. Eligibility involves more than the BMI figure, which is why the prescriber reviews the full picture. The Wegovy versus Mounjaro overview covers efficacy, NHS availability and cost context if you want the broader comparison before your consultation.

If cost is also part of the decision, the cost comparison between Mounjaro and Wegovy lays out the market context plainly. And if you'd like to understand who reviews your case at nume, our clinical team page introduces the prescribers behind the decisions. Which medicine suits you is a clinical decision our prescribers make with you, not one a comparison article can settle. Check your eligibility and start your free consultation to have that conversation with a real clinician.