Mounjaro side effects: what is common, what is serious?

The following table summarises the side effects from the European prescribing information (EMA). Some frequencies differ depending on the indication: in weight management, for example, vomiting, abdominal pain and constipation were very common, in type 2 diabetes “only” common.

The table is a simplified summary. The package leaflet of your product is what counts. This is general information and not medical advice.

Tirzepatide slows gastric emptying – this makes you feel full, but can put a strain on your stomach. According to the prescribing information, in the weight management trials 55.6 to 60.8 % of participants on tirzepatide had gastrointestinal complaints, compared with 30.3 % on placebo. They were mostly mild to moderate, occurred mainly during the dose-increase phase and became less frequent over time.

In detail, with practical tips:

• Nausea with the weight-loss injection
• Constipation on Mounjaro
• Heartburn and reflux

Important before surgery: because of delayed gastric emptying, cases of aspiration under general anaesthesia or deep sedation have been reported with GLP-1 medications. Before any procedure, tell them that you are taking Mounjaro.

Many complaints are linked to dose increases: according to the prescribing information, treatment starts at 2.5 mg once a week, and the dose can be increased in 2.5 mg steps after at least 4 weeks each. Gastrointestinal complaints occur more often during these phases in particular. How fast the dose is increased is decided by your doctor. If complaints are severe after an increase, speak up rather than silently putting up with it. Details: Mounjaro dosage.

In general, many people find these help: smaller portions, eating slowly, avoiding fatty and very large meals and stopping as soon as you're full. A high-protein diet also protects your muscles – more in Nutrition with the weight-loss injection.

Vomiting, diarrhoea and nausea can lead to fluid loss (dehydration). The prescribing information warns that this can worsen kidney function, up to acute kidney failure. Drinking enough is therefore not a minor matter – especially at the beginning and when you have gastrointestinal complaints. More on this: Drinking properly with the weight-loss injection.

Low blood sugar (hypoglycaemia): The risk rises mainly when Mounjaro is taken together with insulin or sulfonylureas. In trials in type 2 diabetes, clinically relevant hypoglycaemia occurred in 10 to 14 % (plus sulfonylurea) and 14 to 19 % (plus basal insulin). The doctor then often adjusts the other medications – don't change them yourself.

Tiredness and dizziness: Tiredness is common; dizziness and low blood pressure occur mainly in people with overweight. This is particularly relevant if you take blood pressure medication. More under Tiredness and headaches.

Hair loss is listed as common in weight management and is often linked to rapid weight loss: Hair loss with the weight-loss injection.

Muscle mass: Muscle loss is not listed as a side effect in the prescribing information, but it is an issue with substantial weight loss. How to counteract it: Muscle loss on GLP-1.

Gallstones and inflammation of the gallbladder are uncommon. According to the prescribing information, gallbladder events in the weight management trials were associated with weight loss. Acute pancreatitis is also uncommon, but serious: if it is suspected, Mounjaro is stopped, and if pancreatitis is confirmed, it must not be restarted.

All the details: Gallbladder and pancreas on GLP-1.

Injection site reactions such as redness or itching are common and usually harmless. Change the site every week – how to do this is explained in the KwikPen instructions. Severe allergic reactions with swelling of the face, lips or throat or shortness of breath are rare, but an emergency.

If you have diabetic retinopathy, mention it before starting. If you take the pill, also read Weight-loss injection and contraception.

Discuss every side effect with your doctor or pharmacy – including those not listed in the package leaflet. In Germany you can also report suspected cases directly yourself: via the joint online portal of the BfArM and the Paul-Ehrlich-Institut (nebenwirkungen.bund.de). Every report helps to better assess the safety of the medication. The portal does not replace personal advice. For the report, it's best to note down the product, dose, date of the last injection, onset and course of the complaints and your other medications.