Both are weekly injections that lower blood sugar and appetite. Mounjaro (tirzepatide) works on two hormone pathways and led to more weight loss in a head-to-head trial. Here is how they compare.
The short answer
Ozempic (semaglutide) mimics one gut hormone, GLP-1. Mounjaro (tirzepatide) mimics two, GIP and GLP-1. Both are once-weekly injections approved for type 2 diabetes, with the same medicines sold for weight management as Wegovy (semaglutide) and Zepbound (tirzepatide). In the 2025 SURMOUNT-5 head-to-head trial, people on tirzepatide lost about 20% of body weight at 72 weeks versus about 14% on semaglutide. Side effects are similar.
Side by side
| Ozempic / Wegovy | Mounjaro / Zepbound | |
|---|---|---|
| Medicine | Semaglutide | Tirzepatide |
| How it works | GLP-1 receptor agonist | Dual GIP and GLP-1 receptor agonist |
| Maker | Novo Nordisk | Eli Lilly |
| How often | Once a week | Once a week |
| Average weight loss (SURMOUNT-5, 72 weeks) | About 13.7% | About 20.2% |
| Common side effects | Nausea, diarrhoea, constipation, vomiting | Nausea, diarrhoea, constipation, vomiting |
| Heart benefit shown in trials | Yes (SELECT trial) | Studies ongoing |
Which works better?
For weight loss, tirzepatide produced more on average in the only large head-to-head trial so far. That does not mean it is right for everyone. Semaglutide has more long-term data, including a proven reduction in heart attacks and strokes in people with heart disease and excess weight. Coverage, supply, cost, side effects and your other health conditions often decide the choice.
The short version
Side effects and safety
Both commonly cause nausea, fullness, constipation or diarrhoea, especially when starting or increasing the dose. Less common but serious risks include pancreatitis, gallbladder problems and dehydration. Neither should be used in pregnancy or by people with a personal or family history of medullary thyroid cancer or MEN2. Both can make oral contraceptives less reliable around dose changes (especially tirzepatide), so ask about a backup method.
Can you switch?
Yes, under medical supervision. Doses are not interchangeable, so your prescriber will choose a starting dose for the new medicine.
Eating on either medicine
Smaller portions, protein at every meal, fibre, fluids and strength training help protect muscle and manage side effects. See our guides on what to eat on a GLP-1 and on nausea and constipation.
Frequently asked questions
Is Mounjaro stronger than Ozempic?
In the SURMOUNT-5 trial, tirzepatide (Mounjaro/Zepbound) led to more weight loss on average than semaglutide (Ozempic/Wegovy): about 20% versus 14%.
Are Ozempic and Wegovy the same drug?
Yes. Both are semaglutide. Ozempic is approved for type 2 diabetes and Wegovy for weight management, at different doses.
Which has fewer side effects, Ozempic or Mounjaro?
Both have similar digestive side effects, mainly nausea, constipation and diarrhoea, which are usually worst when starting or increasing the dose.
Can I switch from Ozempic to Mounjaro?
Yes, with your prescriber’s guidance. The doses are not equivalent, so the new medicine starts at a dose they choose.
Eat well on either medicine
Whichever medicine you take, protein-first meals help protect muscle when appetite is low. Start with the free GLP-1 Starter Kit.
