Thinking of moving from Mounjaro to Wegovy? Here's what the evidence actually says

Are Mounjaro and Wegovy the same kind of medicine?

No, and that difference matters clinically. Wegovy contains semaglutide, a GLP-1 receptor agonist made by Novo Nordisk. It mimics a gut hormone that signals fullness and slows gastric emptying. Mounjaro contains tirzepatide, made by Eli Lilly, which activates two receptors simultaneously: GLP-1 and GIP. The addition of the GIP pathway appears to produce a stronger appetite-suppressing and metabolic effect in most people, which is reflected in the trial data.

Both medicines are licensed in the UK for weight management in adults with a BMI of 30 or above, or 27 and above alongside a weight-related health condition such as high blood pressure or type 2 diabetes. Both are Black Triangle medicines, meaning the MHRA monitors them more closely while post-launch evidence accumulates. You can read the clinical profile of each on the NHS tirzepatide medicine page and the NHS semaglutide medicine page.

Because the mechanisms differ, switching from one to the other is not simply swapping like for like. A prescriber will review your current dose, your response to treatment and any side effects before deciding whether a switch makes clinical sense, and what starting point would be appropriate on the new medicine. Our guide to moving from Mounjaro to Wegovy covers that process in more detail.

What do the trial results show when you put Mounjaro and Wegovy side by side?

The most direct evidence comes from SURMOUNT-5, a 72-week open-label head-to-head trial published in the New England Journal of Medicine in 2025, involving 751 adults with obesity and no diabetes. Tirzepatide produced a greater average percentage weight loss than semaglutide 2.4mg across the trial period, and our detailed look at how Mounjaro fares against Wegovy walks through what those results mean in practice. NICE's appraisal of tirzepatide noted this result in its committee discussions and acknowledged that indirect comparisons also favour tirzepatide.

Taken separately, SURMOUNT-1 (tirzepatide at its highest dose) reported average body-weight reductions of around 20 to 21% over 72 weeks in clinical trials. STEP 1 (semaglutide 2.4mg) reported around 15% average reduction over 68 weeks. A newer 7.2mg Wegovy dose, approved by the MHRA in April 2026, reported approximately 20.7% average loss over 72 weeks in its supporting trials, narrowing the gap considerably, and you can explore how that shifts the picture in our guide to Wegovy versus Mounjaro. You can check the NICE appraisal of tirzepatide (TA1026) for the committee's full review of the comparative evidence.

Numbers from trials apply to the populations studied under controlled conditions. Individual results vary.

Is it the side effects that make people consider switching between them?

Sometimes, yes. Both medicines share a broadly similar side-effect profile, dominated by gastrointestinal symptoms: nausea, loose stools, constipation, reflux and fatigue, most noticeable after starting or moving to a higher dose. For some people, one medicine sits noticeably better than the other, though predicting which that will be in advance is not straightforward.

There are also practical differences. Tirzepatide uses a KwikPen device where each pen contains four weekly doses. Wegovy uses single-dose pens. Some people find the pen format affects their willingness to stick with treatment, particularly when travelling. Both pens live in the fridge; neither should be left at room temperature beyond the window stated in the Patient Information Leaflet.

The MHRA issued a Drug Safety Update in January 2026 highlighting that acute pancreatitis is a known, infrequent but serious risk with GLP-1 medicines. Severe persistent stomach pain that radiates to the back warrants urgent medical attention. You can report suspected side effects using the Yellow Card scheme. Any decision to switch because of side effects should go through a prescriber, not be made unilaterally.

Does the cost difference between Wegovy and Mounjaro affect which one people choose?

It does, and the gap has widened since Eli Lilly raised Mounjaro's UK list price in September 2025, with reported private prices ranging from roughly £149 to £375 per month depending on dose and provider. Wegovy pricing sits at a different point in the market, and if you want a thorough breakdown of how the two stack up on value as well as efficacy, our Wegovy versus Mounjaro cost and clinical comparison covers both angles in full. Our page on why Wegovy is typically priced lower than Mounjaro unpacks the reasons behind that gap.

Cost is a real-world factor, but it is worth treating it as one input rather than the deciding one. The right medicine at the wrong price point for your situation is not a good outcome; nor is the cheaper medicine if your body tolerates it poorly or it produces less response for you specifically. At nume, one price covers the consultation, prescription, treatment and aftercare: no hidden charges, no subscription. We are not competing to be the cheapest option on the market, and we are not going to pretend otherwise.

To understand the full comparison across all the dimensions that matter to you, our prescribers work through that at consultation. There is a more detailed breakdown available on our Wegovy versus Mounjaro comparison page, and you can read about our clinical team's approach on the clinical team profile. If you are ready to find out which is the right fit for you, the place to start is a free consultation with our prescribers.