Mounjaro®
Starting from £179.99/mo
Start journey Learn moreWhat the trial data and real-world experience say about each medicine
You've read the reviews, here's what the clinical evidence adds
You've probably seen the comment threads: people describing dramatic results on tirzepatide, others saying semaglutide was more manageable in the early weeks. Both responses are credible. The medicines work through related but distinct mechanisms. Mounjaro activates two gut-hormone receptors (GIP and GLP-1) whereas Wegovy targets the GLP-1 receptor alone, as described on the NHS tirzepatide medicines page. That dual action is why tirzepatide's average weight-loss figures sit higher in trials.
In SURMOUNT-1 (72 weeks, 2,539 adults with obesity), tirzepatide at its highest dose produced average body-weight reductions of around 20–21%. STEP 1 (68 weeks) recorded approximately 15% average weight loss with semaglutide 2.4mg. Those aren't head-to-head numbers from the same population (they come from separate trials with different designs) so treat them as context rather than a direct verdict. The SURMOUNT-5 trial provides the fairest comparison because it randomised the same pool of participants to one medicine or the other.
As for which side effects people mention most: both have a GI-led profile. Nausea is common after starting or a dose increase, usually settling within a couple of weeks. Some patient accounts describe tirzepatide's nausea as slightly sharper early on; others find the longer titration schedule on Mounjaro (starting at 2.5mg) gives their body more time to adjust. Semaglutide begins at 0.25mg and climbs through five steps to 2.4mg maintenance. Individual tolerance varies considerably, and if you want to read how real patients describe that experience when moving between the two, our page collecting switching from Mounjaro to Wegovy reviews offers a useful range of first-hand accounts. If you want a closer look at how the two medicines stack up cost-wise, our Wegovy vs Mounjaro cost comparison covers the pricing landscape in detail.
The comparison table: key facts side by side
The table below pulls together the core clinical facts. All percentages come from the licensed trial programmes cited above; the NICE appraisals TA1026 (tirzepatide) and TA875 (semaglutide) contain the full evidence reviews.
| Feature | Mounjaro (tirzepatide) | Wegovy (semaglutide injection) |
|---|---|---|
| Mechanism | Dual GIP and GLP-1 receptor agonist | GLP-1 receptor agonist |
| Average weight loss in trials | ~20–21% at 15mg (SURMOUNT-1, 72 weeks) | ~15% at 2.4mg (STEP 1, 68 weeks) |
| Head-to-head result (SURMOUNT-5, NEJM 2025) | Greater average reduction | Lower average reduction |
| UK licensed strengths | 2.5, 5, 7.5, 10, 12.5, 15 mg | 0.25 mg to 2.4 mg (and 7.2 mg, approved Apr 2026) |
| Starting dose | 2.5 mg (tolerability) | 0.25 mg |
| NICE recommendation | TA1026 (BMI ≥35 + ≥1 comorbidity (NHS pathway) | TA875) BMI ≥35, specialist service, max 2 years |
| Black Triangle status | Yes (▼) | Yes (▼) |
One practical point worth noting: a 7.2mg Wegovy pen, approved by the MHRA in April 2026 as a dedicated single weekly injection, brings semaglutide's top dose closer to tirzepatide's results. Trials reported around 20.7% average weight loss over 72 weeks at 7.2mg. The gap narrows, though it doesn't close entirely. For a deeper look at how switching between the two works in practice, the page on switching from Wegovy to Mounjaro is worth reading.
What reviews often miss: eligibility, context and the prescriber's role
Reviews are written by individuals. A five-star account of Mounjaro may come from someone who had tried Wegovy and hit a plateau, or who had a comorbidity that shaped their response. A cautious Wegovy review may reflect early nausea that resolved at week three. Neither tells you what will happen to you specifically.
Both medicines are licensed for adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for certain ethnic backgrounds under UK guidance. If you are still weighing up which option fits your circumstances, our guide to Wegovy or Mounjaro walks through the practical considerations that can help you have a more informed conversation with a prescriber. What reviews rarely capture is the prescriber's view of someone's full history (existing medications, tolerance signals, comorbidities) all of which shape which medicine is appropriate and at what pace the dose moves.
It is also worth being clear on what Ozempic is: semaglutide, but licensed for type 2 diabetes rather than weight loss. You will see it in reviews and forums, but it is not prescribed for weight management. Our page on Mounjaro vs Ozempic explains the distinction properly.
The question of which medicine suits you is one our prescribers work through at consultation, and our detailed Wegovy vs Mounjaro comparison sets out the clinical differences side by side so you can arrive at that conversation better prepared. When your order arrives (a plain box, no branding, DPD tracking to your phone) what's inside reflects a clinical decision made for your situation. Which suits you is a clinical decision our prescribers make with you. To start that conversation, visit our weight-loss treatments page and check your eligibility. You can also learn more about the people making those decisions on the clinical team profile.
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