Wegovy or Mounjaro: which has fewer side effects?

The decision most people are really making

When patients ask what has less side effects (Wegovy or Mounjaro) they usually mean one of two things: which is less likely to make me feel rough in the first few weeks, and which carries fewer risks longer term. Those are different questions, and they deserve separate answers.

For day-to-day tolerability in early treatment, nausea is the dominant concern with both medicines. Wegovy (semaglutide) acts on a single gut-hormone pathway, the GLP-1 receptor. Mounjaro (tirzepatide) activates two pathways — GLP-1 and GIP. That dual action is why Mounjaro tends to produce greater average weight loss in trials, but it also means the mechanism is more potent, which for some people translates to more noticeable gastrointestinal effects at higher doses.

The NHS medicines information for tirzepatide and for semaglutide both list nausea, vomiting, diarrhoea, constipation, indigestion and burping as common side effects. The lists overlap substantially, which tells you something useful: choosing on side-effect grounds alone is rarely as straightforward as it sounds.

The decision is better framed around your individual history, your BMI, any conditions you already have, and how you tend to respond to medicines generally. That is exactly the territory a prescriber covers in a clinical assessment. If you are weighing up what has more side effects, Mounjaro or Wegovy, it helps to look at both medicines side by side before speaking to a prescriber. For more on how the two medicines compare overall, the Wegovy vs Mounjaro overview sets out the wider picture.

What the trial evidence actually shows

Side effects were tracked rigorously in the large clinical programmes for both medicines, so there is real data to draw on, not just anecdote.

In the SURMOUNT-1 trial (tirzepatide, published in the New England Journal of Medicine), gastrointestinal side effects were reported by a meaningful proportion of participants, most commonly during the titration phase and at higher doses. Crucially, the majority were described as mild to moderate in severity, and most settled as the body adjusted. Rates of discontinuation due to side effects were comparable to those seen in the semaglutide STEP trials.

The SURMOUNT-5 head-to-head trial compared tirzepatide directly against semaglutide 2.4mg over 72 weeks. Tirzepatide produced greater average weight loss (a finding subsequently reflected in NICE's appraisal of tirzepatide (TA1026)) but the trial did not establish that one medicine had meaningfully fewer side effects than the other across the study population as a whole. Both arms saw similar patterns of early GI symptoms that largely resolved with time.

One practical difference worth noting: because Mounjaro starts at 2.5mg (a tolerability dose whose job is to settle your system rather than drive weight loss) and titrates slowly, many people find the initial adjustment gentler than they expected. Wegovy follows a similarly gradual titration from 0.25mg upward. Both schedules exist precisely to reduce side-effect burden, but the pace of increase and the individual's response still vary.

You can read a closer examination of the numbers in the direct side-effect comparison for Mounjaro and Wegovy.

A side-by-side look at the key differences

The table below summarises the most clinically relevant points. Numbers from trial publications and NICE appraisals; individual experience will differ.

The oral contraceptive point deserves a sentence of its own. NHS guidance advises that women on the pill using Mounjaro should add a non-oral contraceptive method for the first four weeks of treatment and for four weeks after any dose increase, because slowed gastric emptying may reduce pill absorption. No equivalent warning applies to Wegovy. If that interaction matters to you, it is worth raising during your consultation, our prescribers discuss it routinely. You can also read more about overall cost considerations on the Wegovy vs Mounjaro cost page.

So which should you choose?

Honestly, this is the question our prescribers are there to answer, and it cannot be answered from a side-effect list alone. A few things genuinely shift the balance.

If you have a history of significant nausea with other medicines, your prescriber may want to start at the lowest possible dose of whichever medicine you try, and go slowly. If you are on oral contraceptives and would find adding a barrier method inconvenient, Wegovy may be simpler from a practical standpoint. If greater average weight loss is the clinical priority and your history supports it, the tirzepatide data is compelling. And if you are already partway through treatment with one medicine and considering switching, that warrants a careful clinical review rather than a switch based on a comparison article, even a thorough one.

Neither medicine is free of side effects. Both are well-studied. The question of whether Wegovy has fewer side effects than Mounjaro does not have a single yes or no answer that holds across every patient. What matters is which medicine is the better clinical fit for you, assessed properly.

If you would like a prescriber at nume's GPhC-registered pharmacy to review your situation, you can check your eligibility and start a free consultation. Consultations are reviewed the same day, a named clinician reads your answers and responds, not a queue of automated checks. Our clinical team is also available if you have questions before you begin.