Weight-loss injections such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) are weekly medicines that mimic gut hormones (GLP-1, and GIP for tirzepatide) to reduce appetite, slow stomach emptying and improve blood sugar. In clinical trials, people lost on average around 15% of body weight with semaglutide 2.4 mg and around 20% with higher doses of tirzepatide over about 68 to 72 weeks, alongside diet and activity changes. They are prescription medicines with real side effects and are not for everyone.
Brand names and uses
| Medicine | Brands | Main licensed use |
|---|---|---|
| Semaglutide | Ozempic | Type 2 diabetes |
| Semaglutide | Wegovy | Weight management |
| Tirzepatide | Mounjaro | Type 2 diabetes (and weight management in some countries) |
| Tirzepatide | Zepbound | Weight management (US) |
Licensing differs by country. Weight-management use is usually for adults with a BMI of 30 or more, or 27 or more with a weight-related condition, alongside lifestyle changes.
Common side effects
- Nausea, vomiting, diarrhoea or constipation, especially when the dose is increased
- Reduced appetite, burping, indigestion
- Tiredness
Serious but less common risks
- Pancreatitis: severe abdominal pain spreading to the back
- Gallbladder problems
- Dehydration and kidney problems from vomiting or diarrhoea
- Low blood sugar when combined with insulin or sulfonylureas
- Muscle loss if protein intake and exercise are low
Who should not use them
- People with a personal or family history of medullary thyroid cancer or MEN2
- Pregnancy and breastfeeding; stop before trying to conceive as advised
- History of pancreatitis needs careful assessment
Practical advice
- Eat smaller meals and stop when full; prioritise protein
- Drink fluids and report persistent vomiting
- Do strength exercise to protect muscle
- Weight often returns if the medicine is stopped without lasting lifestyle changes
- Tell your anaesthetist before surgery; these drugs slow stomach emptying
Beware of fake and compounded products
Counterfeit pens and unregulated “semaglutide” sold online or on social media have caused harm. Only use medicines prescribed by a licensed healthcare provider and dispensed by a registered pharmacy.
Frequently asked questions
Is Ozempic the same as Wegovy?
Both contain semaglutide, but they are licensed for different uses and doses.
Do you need to diet on weight-loss injections?
Yes. They work best with a healthy diet and activity, and these habits help maintain weight after stopping.
Related reading: Diabetes diet · Acute pancreatitis
Updated 5 November 2026. This guide is for education; talk to your nurse or healthcare provider about whether these medicines suit you.
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