Mounjaro or Wegovy: which has more side effects?

Step 1: recognise what they have in common

Start here, because most people arrive at this question expecting a stark difference. In practice, the two medicines overlap considerably. Both work by activating GLP-1 receptors, slowing gastric emptying and suppressing appetite through gut-hormone pathways. The result is a predictable cluster of gastrointestinal effects: nausea tends to be the most common, followed by loose stools or constipation, burping, and reflux. Fatigue, headache and dizziness also appear in trial data for both.

The timing follows the same pattern too. Symptoms are most noticeable in the first days after starting or after a dose increase, then typically settle within one to two weeks as the body adjusts. You can read the full NHS patient-level overview of tirzepatide's side-effect list on the NHS tirzepatide medicines page, and the comparable semaglutide profile on the NHS semaglutide medicines page, both are worth a read before starting either treatment.

The practical takeaway from this step: choosing between these medicines purely to avoid GI side effects is rarely the deciding factor, because the difference in type of reaction is small. If you want a detailed look at Wegovy v Mounjaro side effects, including how the reactions compare across the full titration journey, that page walks through the evidence in one place. The question is really about frequency, mechanism, and individual tolerance, which is where they diverge.

Step 2: look at where they differ in the data

Mounjaro activates two receptors (GLP-1 and GIP) while Wegovy activates one (GLP-1 only). This dual action is associated with greater average weight loss in head-to-head trials, including the SURMOUNT-5 study published in the New England Journal of Medicine (2025), which found tirzepatide produced a larger average reduction than semaglutide 2.4mg over 72 weeks.

Greater potency at higher doses can mean more pronounced GI effects during titration, though this is not universal. In SURMOUNT-1 (tirzepatide, 2,539 participants), gastrointestinal events were the most frequently reported adverse effects, with nausea affecting roughly 30–45% of participants at therapeutic doses, broadly similar to rates seen in Wegovy's STEP 1 trial. The difference that emerges in clinical practice is often about the titration schedule: both treatments start low and increase gradually over months, and how a patient tolerates each step is individual.

Mounjaro users should also be aware of one interaction Wegovy does not carry to the same degree: the absorption of oral medicines, including the contraceptive pill, may be reduced in the first four weeks of treatment and after each dose increase. The NHS England guidance on weight-management injections recommends adding a non-oral contraceptive method during those windows, and suggests considering transdermal HRT (patches or gels) for the same reason. This is a pharmacological difference worth factoring in, not just a side-effect statistic.

On the safety monitoring side, in January 2026 the MHRA issued a Drug Safety Update highlighting acute pancreatitis as a known but infrequent risk for GLP-1 medicines as a class. The symptom to act on promptly is severe, persistent abdominal pain, especially pain that radiates to the back. This applies to both Mounjaro and Wegovy. Patients can report any suspected reactions at yellowcard.mhra.gov.uk.

Step 3: compare the profiles side by side

Many people searching this topic want to know what has less side effects, Wegovy or Mounjaro, and that page addresses the question directly using trial data rather than anecdote. You can also explore a broader breakdown of how the two treatments compare on the Wegovy vs Mounjaro side effects page, or see the full head-to-head across other factors on our Wegovy vs Mounjaro overview.

Step 4: what this means for your decision

If you've spent time on forums or asked friends about this, you've probably heard strong opinions in both directions. That's understandable. Side-effect experience is genuinely personal, and one person's easy ride on Mounjaro is another person's reason to switch. For a closer look at which has more side effects, Mounjaro or Wegovy, that page examines the frequency data from the key clinical trials so you can weigh the numbers yourself. What the clinical picture actually supports is this: neither medicine has a dramatically worse safety record than the other for most people; the differences lie in mechanism, potency, and specific interactions rather than in a blanket verdict.

A prescriber looking at your full health picture, including your current medications (particularly the contraceptive pill or HRT), your medical history, and your reasons for treatment, is far better placed to identify which option fits you than any online comparison. Our clinical team reviews that picture personally, not by algorithm.

If cost is part of your thinking alongside tolerability, the Wegovy vs Mounjaro cost page covers that angle honestly. And if you have questions before starting, our FAQs address the most common ones. When you're ready, the next step is a free consultation, the prescriber goes through suitability in detail and chooses the appropriate starting treatment with you. Check your eligibility and start your free consultation.