Mounjaro®
Starting from £179.99/mo
Start journey Learn moreHow the two medicines compare: mechanisms, trial results and eligibility side by side
The myth worth clearing up first: 'semaglutide and Mounjaro are basically the same thing'
This one comes up constantly, and it's understandable, both are weekly injections, both reduce appetite, both carry a prescription requirement, and both sit inside the GLP-1 class of medicines in most news coverage. The reality is more precise. Semaglutide (the active ingredient in Wegovy) targets a single receptor, GLP-1, slowing gastric emptying and signalling fullness to the brain. Tirzepatide (Mounjaro) hits two: GLP-1 and GIP. The addition of GIP activity appears to compound the appetite-reduction effect beyond what GLP-1 alone achieves.
That dual mechanism isn't just a marketing distinction. It's reflected in the trial data. In the SURMOUNT-1 trial, tirzepatide at its highest dose produced an average body-weight reduction of around 20–21% over 72 weeks, results that were larger than anything semaglutide 2.4mg had demonstrated in its own licensing trials. And in 2025, the SURMOUNT-5 head-to-head trial directly compared the two in adults with obesity and found tirzepatide produced greater average weight loss than semaglutide 2.4mg, as discussed in our detailed tirzepatide vs semaglutide comparison.
If you want to understand how tirzepatide and semaglutide compare for weight loss across the key evidence, that's a useful place to start before weighing up which to ask about, because these are genuinely different medicines with different evidence bases. That said, one isn't universally 'better', which suits you is a clinical judgement, and both are prescription-only.
What the numbers actually say: a side-by-side look
The table below draws on trial data and UK regulatory approvals. Numbers are trial averages, not predictions for any individual, your result will depend on your starting point, your lifestyle changes alongside treatment, and how long you stay on the medicine.
| Feature | Semaglutide (Wegovy injection) | Tirzepatide (Mounjaro) |
|---|---|---|
| Mechanism | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Average weight loss in trials | ~15% over 68 weeks at 2.4mg (STEP 1, NEJM) | ~20–21% over 72 weeks at 15mg (SURMOUNT-1, NEJM) |
| Head-to-head result (SURMOUNT-5, 2025) | Comparator arm | Greater average loss vs semaglutide 2.4mg |
| UK licence (weight management) | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30, or ≥27 with a weight-related condition |
| NICE recommendation | TA875: up to 2 years, specialist weight management service | TA1026: within primary or specialist care, no 2-year cap |
| Dosing format | Weekly injection; doses from 0.25mg up to 2.4mg (or 7.2mg with the newer pen) | Weekly injection; doses from 2.5mg up to 15mg |
One practical note: the specifics of how Wegovy and Mounjaro compare in everyday use (pen design, titration pace, injection technique) are worth reading if you're deciding which to ask your prescriber about.
Side effects, eligibility and the NICE picture
Both medicines share a broadly similar side-effect profile, led by gastrointestinal symptoms: nausea, constipation, diarrhoea, indigestion and reduced appetite are the most common, particularly after starting or a dose increase, and often settle within a couple of weeks. The NHS medicines pages for tirzepatide and for semaglutide detail these alongside the rarer but serious signs (including acute pancreatitis, which the MHRA highlighted in a 2026 Drug Safety Update) that warrant urgent medical attention.
On eligibility, both share the licensed threshold of BMI ≥30, or ≥27 alongside a qualifying condition such as hypertension, high cholesterol, obstructive sleep apnoea or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. Where they differ is in the NICE picture. Wegovy (TA875) is recommended for NHS use for a maximum of two years, within a specialist weight management service. Mounjaro (TA1026, updated September 2025) carries no equivalent two-year cap and is being rolled out through both specialist and primary care. NICE's appraisal of tirzepatide sets out the NHS eligibility criteria in full.
It's also worth being clear on one thing that confuses a lot of people: Ozempic is also semaglutide, but it's licensed for type 2 diabetes, not weight loss. The Mounjaro vs Ozempic page explains that distinction. For weight management, the relevant semaglutide product is Wegovy.
Which should you ask about, and how does a prescriber decide?
The question 'is semaglutide or Mounjaro better for weight loss' rarely has a single clean answer, it depends on your medical history, any conditions you're managing, medicines you already take, and practical factors like how you feel about injections. If you want a fuller picture before speaking to a prescriber, our Wegovy vs Mounjaro for weight loss guide walks through how the trial data and real-world considerations stack up side by side. A prescriber looks at the individual.
At nume, every consultation is reviewed the same day by a GPhC-registered Independent Prescriber. You don't get a bot's output or an auto-approval; a real clinician reads your answers and makes a clinical decision. If the evidence genuinely supports one medicine over another for your situation, that's the conversation. You can check your eligibility and start a free consultation without any commitment. For a broader view of how the two medicines sit within the current treatment landscape, the weight-loss treatment overview is a good starting point, and you can read more about the differences between Mounjaro and Wegovy in practical terms before you decide what to ask.
Which suits you is a clinical decision our prescribers make with you, not something to resolve by reading a comparison page alone.
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