Mounjaro vs Ozempic is a comparison between two different medicines. Mounjaro contains tirzepatide, which acts on two hormone receptors (GIP and GLP-1), while Ozempic contains semaglutide, which acts on one (GLP-1). In the UK, Ozempic is licensed for type 2 diabetes, whereas Mounjaro is licensed for both type 2 diabetes and weight management. The weight-management form of semaglutide is Wegovy, the same ingredient at a higher top dose. In the head-to-head weight-loss trial against semaglutide (SURMOUNT-5), tirzepatide produced greater average weight loss, and both cause similar digestive side effects. Which is right for you depends on your condition, suitability and your prescriber’s advice.
Mounjaro is made by Eli Lilly and contains tirzepatide. Ozempic is made by Novo Nordisk and contains semaglutide. Novo Nordisk also makes Wegovy, which contains the same active ingredient as Ozempic but is licensed for weight management and goes up to a higher dose. So for weight loss, the more accurate comparison is usually Mounjaro versus Wegovy, while Mounjaro versus Ozempic is the one people search for.
| Mounjaro | Ozempic | |
|---|---|---|
| Active ingredient | Tirzepatide | Semaglutide |
| Made by | Eli Lilly | Novo Nordisk |
| How it works | Activates GIP and GLP-1 receptors | Activates GLP-1 receptors |
| UK licensed use | Type 2 diabetes and weight management | Type 2 diabetes |
| How it is taken | Once-weekly injection (KwikPen) | Once-weekly injection (pen) |
| Dose range | 2.5 mg to 15 mg weekly | 0.25 mg to 2 mg weekly |
| Weight-management version of the same medicine | Mounjaro | Wegovy (semaglutide up to 2.4 mg) |
A licence describes the conditions a medicine has been tested and approved for. Ozempic’s UK licence is for adults whose type 2 diabetes is not well controlled. It is not licensed for weight management, so using it for weight loss alone would be off-label. Wegovy contains semaglutide at doses studied and licensed for weight management in adults with obesity, or with overweight and a weight-related condition. Mounjaro holds a licence covering both type 2 diabetes and weight management.
During previous supply problems, UK health authorities warned that off-label use of diabetes medicines for weight loss risked shortages for people who rely on them for diabetes. If you are choosing a semaglutide medicine for weight management, Wegovy is the licensed product.
How They Work: One Hormone or Two?Both medicines copy gut hormones released after eating. Semaglutide copies GLP-1, which reduces appetite, slows how quickly the stomach empties and helps the pancreas release insulin when blood sugar is high. Tirzepatide copies GLP-1 and also GIP, a second gut hormone. The idea behind the dual action is that GIP adds to the effects on appetite and insulin response. Both slow stomach emptying, which is part of why you feel full sooner and also why digestive side effects occur.
Lining up numbers from different trials can mislead, because the people, doses and designs differ. The most useful evidence comes from trials that compare the two medicines directly.
Bars drawn to scale within each trial. The two trials used different people, doses and designs, so do not compare across them.
SURMOUNT-5: weight management
This 72-week trial included 751 adults with obesity and no diabetes. They took tirzepatide (10 mg or 15 mg) or semaglutide (1.7 mg or 2.4 mg) at their maximum tolerated dose. Average weight loss was 20.2% with tirzepatide and 13.7% with semaglutide, about 22.8 kg against 15.0 kg. Waist circumference fell by about 18.4 cm against 13.0 cm. Fewer people stopped tirzepatide because of digestive side effects (2.7% against 5.6%). The semaglutide used was at Wegovy doses, not Ozempic doses, so this is really a Mounjaro versus Wegovy result.
SURPASS-2: type 2 diabetes
This 40-week trial compared tirzepatide with semaglutide 1 mg, a dose in the Ozempic range, in adults with type 2 diabetes. All three tirzepatide doses lowered HbA1c more than semaglutide 1 mg, and average weight loss was greater with tirzepatide, ranging from about 7.6 to 11.2 kg against about 5.7 kg.
Reading the numbers
Averages hide wide individual variation. Some people lose far more than average and some lose less, whichever medicine they take, and real-world results can differ from trials.
Both are weekly injections that start low and increase gradually to reduce side effects. Do not switch medicines or convert doses yourself, because the starting point after a change is decided by a prescriber. See our dose guides for Mounjaro and Wegovy.
| Feature | Mounjaro | Ozempic |
|---|---|---|
| Starting dose | 2.5 mg weekly for 4 weeks | 0.25 mg weekly for 4 weeks |
| Increase steps | 2.5 mg steps, at least 4 weeks apart | Steps through 0.5 mg, 1 mg and 2 mg |
| Top dose | 15 mg weekly | 2 mg weekly |
| Missed dose | Take within 4 days, otherwise skip | Follow the Ozempic leaflet |
| Pen | KwikPen containing several weekly doses | Multi-dose pen |
The profiles are similar because both are GLP-1 based. Nausea, vomiting, diarrhoea and constipation are very common with each, usually strongest at the start and after dose increases. Gallstones, acute pancreatitis (uncommon), dehydration, injection site reactions and hair loss with rapid weight loss are shared concerns.
| Side effect | Mounjaro | Semaglutide medicines |
|---|---|---|
| Nausea, vomiting, diarrhoea, constipation | Very common | Very common |
| Fatigue | Very common | Very common |
| Gallstones | Gallbladder events rise with weight lost | Common |
| Acute pancreatitis | Uncommon | Uncommon |
| Hair loss | Common | Common |
| Heart rate increase | Common | Uncommon (Wegovy) |
One practical difference is the contraceptive pill. Mounjaro’s product information advises women who use oral contraception to add a barrier method or switch to a non-oral method for 4 weeks after starting and after each dose increase. See our guide to Mounjaro and the contraceptive pill.
How to ChooseThe question is rarely which is better in the abstract. It is which suits you. Your prescriber will consider:
- Your condition: type 2 diabetes, weight management or both
- Whether the medicine is licensed for that purpose
- Your medical history, including pancreatitis, gallbladder disease, kidney problems and diabetic eye disease
- Other medicines, especially insulin, sulphonylureas and the contraceptive pill
- How you tolerated any previous GLP-1 medicine
- Availability and cost
For a like-for-like weight-loss comparison, see our guide to Mounjaro vs Wegovy, and for cost, Mounjaro costs and Wegovy costs.
Common Myths- “Ozempic and Wegovy are different drugs.” They are the same active ingredient, semaglutide, at different dose ranges and with different licences.
- “Mounjaro is just a stronger Ozempic.” It is a different molecule with a dual mechanism.
- “A medicine that works better on average will work better for me.” Individual response varies widely.
- “Ozempic is a safe shortcut for weight loss.” Prescription-only medicines should only be used under clinical supervision and within an appropriate licence.
The bottom line
Mounjaro and Ozempic are different medicines. Tirzepatide acts on two hormone pathways and semaglutide on one. Their UK licences differ: Ozempic for type 2 diabetes, Wegovy (semaglutide) for weight management, and Mounjaro for both. Head-to-head trials favour tirzepatide for average weight loss, but suitability, safety and your own response decide which is right for you.
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Start Your Free Online Consultation Use code SWITCH10 if you're switching from another provider Happy Pharmacy is a GPhC-registered pharmacy (No. 9013192). Superintendent Pharmacist: Palvinder Deol. Rated 4.8★ Excellent on Trustpilot- Mounjaro (tirzepatide) KwikPen: UK Summary of Product Characteristics. electronic Medicines Compendium (emc).
- Wegovy (semaglutide) FlexTouch: UK Summary of Product Characteristics. emc.
- Ozempic (semaglutide): UK Summary of Product Characteristics (indications). emc.
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med. 2025;393(1):26-36.
- Frías JP, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2). N Engl J Med. 2021;385:503-515.
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205-216.
- MHRA / NHS England. National Patient Safety Alert on shortage of GLP-1 receptor agonists (2023).