Ozempic vs Mounjaro: which weight-loss jab works better?
Both are weekly injections that can help with weight loss and type 2 diabetes. Here's how they compare, in plain English.
Medically reviewed by Dr LJ Ncube, MBChB · Updated November 2026
The short answer
Ozempic contains semaglutide. Mounjaro contains tirzepatide. Both reduce appetite and help control blood sugar. In a head-to-head trial, people on tirzepatide lost more weight on average, but both work well, and the right one depends on your health, side effects, cost and availability.
How they work
Semaglutide copies one gut hormone, GLP-1, which tells your brain you're full and helps your body release insulin. Tirzepatide copies two hormones, GLP-1 and GIP, which is thought to be why it tends to cause more weight loss.
Show as a table
| Tirzepatide (Mounjaro) | 20.2% |
| Semaglutide (Wegovy) | 13.7% |
Source: Aronne LJ, et al. N Engl J Med. 2025.
Side by side
| Semaglutide | Tirzepatide | |
|---|---|---|
| Brand names | Ozempic (diabetes), Wegovy (weight loss), Rybelsus (tablet) | Mounjaro |
| How it's taken | Injection once a week (or a daily tablet) | Injection once a week |
| Average weight loss in trials | About 15% of body weight over 68 weeks | About 20% at the highest dose over 72 weeks |
| Head-to-head trial (72 weeks) | About 14% weight loss | About 20% weight loss |
| Common side effects | Nausea, diarrhoea, constipation, feeling full | Similar, and similar frequency |
| Starting dose | Low dose, increased about every 4 weeks | Low dose, increased about every 4 weeks |
Trial results are averages from large studies where people also changed their diet and activity. Your result may be more or less.
Who they're for
Doctors usually consider these medicines for adults with:
- A BMI of 30 or more, or
- A BMI of 27 or more with a weight-related condition, such as high blood pressure, type 2 diabetes or sleep apnoea
They aren't suitable if you're pregnant, breastfeeding or trying to conceive, if you or a close relative have had medullary thyroid cancer or MEN2, or if you've had pancreatitis.
Things people don't always know
- Weight often comes back after stopping, unless eating and activity habits have changed too.
- Tirzepatide can make the contraceptive pill less reliable for a few weeks after starting and after each dose increase. Use condoms as well during those times.
- Losing weight fast without enough protein and exercise can mean losing muscle as well as fat.
- Buy only from a pharmacy with a prescription. Fake pens sold online have caused serious harm.
Which is right for you?
That depends on your weight, other conditions, current medicines, how you cope with side effects, and cost. A doctor can help you weigh these up, and medication works best as part of a plan that includes nutrition and activity.
Answer a few questions online and our doctor will reply on WhatsApp, usually within 24 hours.
Common questions
Is Ozempic the same as Wegovy?
Both contain semaglutide. Ozempic is licensed for type 2 diabetes and Wegovy for weight loss, at a higher top dose.
Can I switch from Ozempic to Mounjaro?
Often, yes, under a doctor's supervision. You usually restart at a lower dose to limit side effects.
How long do I need to take it?
There's no fixed length. Many people need longer-term treatment to keep the weight off. Your doctor will plan this with you.
Related
Sources
We base our guides on peer-reviewed research and guidance from health authorities. Where studies disagree or evidence is limited, we say so.
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021. PubMed
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022. PubMed
- Aronne LJ, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med. 2025. PubMed
- Wilding JPH, et al. Weight regain after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022. PubMed
- UK Medicines and Healthcare products Regulatory Agency. GLP-1 medicines for weight loss and diabetes: what you need to know. gov.uk
This guide is general information, not advice for your situation. Speak to a doctor before starting or changing any medicine.
