Are weight loss injections safe? Side effects, and who should avoid them
Medically reviewed and approved by Dr Reina Punj, MBBS, PG Diploma in Endocrinology (University of South Wales, UK), Lead Physician, Lean Life. Approved on 24 October 2026.
Key points
- Semaglutide (Wegovy) and tirzepatide (Mounjaro) are approved in India for weight management, under a doctor's prescription.
- The most common side effects are stomach-related: nausea, diarrhoea, vomiting and constipation. They are usually worst when the dose goes up.
- They are not for anyone who is pregnant, or has a personal or family history of medullary thyroid cancer or MEN2.
- Starting low, increasing slowly and having regular check-ins is what keeps treatment safe.
What these injections are
Weight loss injections in India today are GLP-1 medicines. Semaglutide copies one gut hormone, GLP-1. Tirzepatide acts on two, GLP-1 and GIP. Both slow how fast your stomach empties and reduce appetite, so you eat less without feeling as hungry. Both are given as a weekly injection under the skin.
In the large trials, people lost around 15% of their body weight on semaglutide 2.4mg over 68 weeks, and around 21% on tirzepatide 15mg over 72 weeks, alongside diet and activity changes. Read how the two compare.
Common side effects
Most side effects affect the stomach and gut, and most are mild to moderate. They are most likely in the first weeks and just after each dose increase.
- Nausea, sometimes with vomiting
- Diarrhoea or constipation
- Stomach pain, bloating or indigestion
- Tiredness and reduced appetite
Eating smaller meals, stopping when full, avoiding very fatty food and drinking enough water all help. If symptoms don't settle, your doctor can hold the dose where it is for longer.
Less common but serious risks
These are rare, but they are why these medicines should only be taken with a doctor's supervision.
- Pancreatitis. Severe stomach pain that spreads to the back, with or without vomiting, needs urgent medical attention.
- Gallbladder problems, including gallstones, especially with rapid weight loss.
- Low blood sugar in people who also take insulin or sulfonylureas for diabetes.
- Dehydration and kidney strain if vomiting or diarrhoea is severe.
- Thyroid tumours. These were seen in rodent studies. It is not known whether this happens in people, which is why anyone with a related history is excluded.
Who should not take them
- Anyone pregnant, trying to get pregnant or breastfeeding
- Anyone with a personal or family history of medullary thyroid cancer, or multiple endocrine neoplasia type 2 (MEN2)
- Anyone who has had a serious allergic reaction to the medicine
- People with a history of pancreatitis need a careful assessment first
Tirzepatide can make the contraceptive pill less reliable for a few weeks after starting and after each dose increase. If you use the pill, your doctor will advise adding a barrier method during those weeks.
How Lean Life keeps treatment safe
Your first call is with a Lean Life advisor, who answers your questions and books you in. Every patient then sees a doctor before anything is prescribed. The doctor takes a full history, check blood tests, start at the lowest dose and only increase when you are tolerating it. Advisors check in between visits, and anything medical goes straight to a doctor. You can reach us on WhatsApp if a side effect worries you.
Questions
Do the side effects go away?
For most people, stomach side effects ease within a few weeks at each dose. If they don't, your doctor can slow the increase or lower the dose.
Will I regain weight if I stop?
Trials show many people regain some weight after stopping. That is why we plan nutrition, strength training and a step-down with you, rather than stopping abruptly.
Are generic semaglutide versions safe?
Generics approved in India contain the same medicine. Some are approved only for type 2 diabetes, not weight management, so your doctor will check which product fits your situation.