GLP-1 side effects and how doctors manage them

Most people on GLP-1 medicines such as semaglutide (Wegovy, Ozempic and generic brands) and tirzepatide (Mounjaro, Yurpeak) have some side effects, especially early on. The good news is that most are mild, predictable and settle with time. A few are rare but important to recognise. Knowing what is normal and what is not helps you stay on treatment safely. For background, read GLP-1 medicines in India.

Why do these medicines cause stomach side effects?

GLP-1 medicines slow down how fast the stomach empties and act on the brain’s fullness and nausea centres. That is part of how they reduce appetite. But if you eat the way you used to, food sits in the stomach longer, and you may feel queasy, bloated or full of gas. The effects are usually strongest in the first few weeks and for a few days after each step up in strength.

What are the common side effects?

• Nausea, the most common, often mild and early
• Vomiting, less common
• Constipation or, in some people, diarrhoea
• Bloating, burping and sulphur-smelling burps
• Acid reflux or heartburn
• Tiredness and reduced appetite in the first weeks
• Mild reactions at the injection site

How do doctors manage them?

Doctors start at a low strength and increase it slowly, step by step. If side effects are troublesome, your doctor may keep you at the same strength for longer, or step back, rather than pushing on. Please do not change your strength on your own.

Practical advice that doctors and dietitians usually give:

• Eat smaller meals and stop as soon as you feel comfortably full.
• Eat slowly and chew well.
• Go easy on fried, oily and very spicy food, such as heavy curries, pakoras and samosas, especially in the first weeks.
• Avoid lying down soon after eating. Have dinner earlier.
• Drink enough water through the day, sipping rather than gulping.
• For constipation, add fibre gradually (vegetables, fruit, isabgol if your doctor agrees) and keep active.
• Make protein a priority at each meal. Read protein and muscle on weight-loss medicines.

Your doctor may also prescribe short-term medicines for nausea, reflux or constipation.

What about gallstones?

Rapid weight loss of any kind increases the risk of gallstones, and GLP-1 medicines have been linked to a small increase in gallbladder problems in clinical trials. Watch for pain under the right ribs, especially after meals, fever or yellow eyes. These need prompt medical review.

What about pancreatitis?

Pancreatitis, inflammation of the pancreas, has been reported in people taking these medicines. It is uncommon, and whether the medicines directly cause it is still debated, but it is serious. The warning sign is severe, constant pain in the upper belly, often spreading to the back, with or without vomiting. If this happens, seek urgent care and tell the doctors you are on a GLP-1 medicine.

Can these medicines cause dehydration or kidney problems?

Severe vomiting or diarrhoea can cause dehydration, which in turn can harm the kidneys, particularly in people who already have kidney disease, are older or take water tablets. If you cannot keep fluids down, contact your doctor the same day.

What about thyroid cancer?

In rodent studies, these medicines caused a rare type of thyroid tumour called medullary thyroid cancer. This has not been clearly shown in humans. As a precaution, they are not used in people with a personal or family history of medullary thyroid cancer or MEN2. Report any new lump in the neck.

What about the eyes?

In people with diabetic eye disease, a rapid fall in blood sugar can briefly worsen the retina, so an eye check is often advised before starting. A rare condition affecting the optic nerve, called NAION, which causes sudden painless vision loss in one eye, has been reported more often in some studies of semaglutide. The absolute risk appears low. Any sudden vision change needs urgent review.

What about hair loss?

Some people notice more hair fall a few months after starting, usually linked to rapid weight loss and lower food intake rather than the medicine directly. Read do weight-loss injections cause hair loss.

What about pregnancy and contraception?

These medicines are not used in pregnancy. If you could become pregnant, use reliable contraception while on them. The product information for semaglutide advises stopping it well before a planned pregnancy because it stays in the body for weeks, so tell your doctor early if you are planning one.

Tirzepatide slows the stomach enough to make the oral contraceptive pill less reliable, especially in the first weeks and after each step up in strength. The product information advises switching to a non-oral method or adding a barrier method such as condoms during those periods. Ask your doctor what is right for you.

Anything else to tell my doctor?

• If you are having surgery, an endoscopy or a procedure under anaesthesia, tell the team you are on a GLP-1 medicine, because food can stay in the stomach longer. They will tell you how to prepare.
• If you also take insulin or sulphonylureas for diabetes, your doctor may need to adjust them to prevent low sugars.

What should you ask your doctor?

• Which side effects should I expect, and for how long?
• What should I do if I cannot keep food or fluids down?
• Do I need an eye check before starting?
• What contraception is best while I am on this medicine?

If side effects are making treatment hard, do not just stop silently. Talk to your doctor, or book a consultation.