Mounjaro, Wegovy and Ozempic are often lumped together as 'weight-loss jabs', but they aren't interchangeable. They involve two different medicines, work in slightly different ways, and — most importantly — are licensed for different things in the UK. This is general information, not medical advice or a recommendation; only a prescriber can decide what's appropriate for you.
The quick answer
There are two underlying drugs here: tirzepatide (Mounjaro) and semaglutide (sold as Wegovy, Ozempic and the tablet Rybelsus).
- Mounjaro (tirzepatide) — weekly injection; licensed in the UK for both type 2 diabetes and weight management.
- Wegovy (semaglutide) — weekly injection; licensed for weight management.
- Ozempic (semaglutide) — weekly injection; licensed for type 2 diabetes only, not weight loss.
- Rybelsus (semaglutide) — a daily tablet; licensed for type 2 diabetes only.
Same family, different drugs
All of these are based on gut hormones that curb appetite and slow stomach emptying. Semaglutide (Wegovy, Ozempic, Rybelsus) is a GLP-1 receptor agonist — it mimics one hormone, GLP-1. Tirzepatide (Mounjaro) is a dual agonist: it acts on two receptors, GIP and GLP-1. That dual action is the main pharmacological difference between Mounjaro and the semaglutide brands.
Which are licensed for weight loss?
This is the part that causes the most confusion. In the UK, Wegovy and Mounjaro are licensed for weight management, whereas Ozempic and Rybelsus are licensed only for type 2 diabetes and should not be prescribed solely for weight loss. Ozempic is sometimes talked about as a weight-loss drug because it contains the same active ingredient as Wegovy, but it is not licensed for that use here.
If you're weighing up eligibility and cost, our eligibility checker explains the general BMI criteria and the cost calculator works out price per dose from a quote.
How they compare on weight loss
A head-to-head trial, SURMOUNT-5, compared the two drugs directly in adults with obesity (without diabetes) over 72 weeks, each titrated to the maximum tolerated dose. Average weight reduction was 20.2% with tirzepatide versus 13.7% with semaglutide. Gastrointestinal side effects were the most common in both groups and were mostly mild to moderate.
Trial averages are not a promise of individual results — response varies a lot from person to person, and the 'best' option is the one a prescriber judges right for you, factoring in your health, tolerance and which medicine you can access. Mounjaro is dosed once weekly; you can turn a dose into KwikPen clicks with the clicks calculator.