If you’re exploring clinician-prescribed weight loss medication in the UK, you’ve likely come across two names: Mounjaro (tirzepatide) and Ozempic (semaglutide). Both are GLP-1 receptor agonists, both are MHRA-approved, and both have impressive clinical trial results. But they work differently — and the right choice depends on your body, your goals, and your medical history.
How They Work
Ozempic mimics a single gut hormone called GLP-1. It slows gastric emptying, reduces appetite, and helps regulate blood sugar. Mounjaro goes further — it’s a dual agonist, targeting both GLP-1 and GIP receptors. This dual mechanism is why clinical trials consistently show higher average weight loss with Mounjaro.
What the Trials Show
The SURMOUNT trials found Mounjaro patients lost an average of 22.5% of their body weight at the highest dose, compared to roughly 15% with Ozempic in the STEP trials. However, individual results vary enormously. Some people respond brilliantly to semaglutide and less well to tirzepatide, and vice versa.
Side Effects
Both medications share similar GI side effects — nausea, constipation, and occasionally diarrhoea, especially during dose titration. Most people find these settle within 4-6 weeks. Your prescribing clinician will start you on a low dose and increase gradually to minimise discomfort.
Cost and Availability
In the UK, both are available through private clinics like Don’t Weight. Mounjaro tends to be slightly more expensive due to its newer patent status. Your clinician will help you weigh up the clinical evidence against practical considerations like budget and treatment timeline.
The Bottom Line
There’s no universally “better” option. The right medication is the one your clinician recommends based on your BMI, medical history, and how your body responds. That’s why we always start with a proper clinical assessment — not a one-size-fits-all prescription.