Common side effects

Nausea, diarrhoea, vomiting, constipation and abdominal discomfort all appear in the UK product information. Other reported effects include indigestion, reflux, burping, tiredness and reactions at the injection site. Frequency figures differ between diabetes and weight management studies, so no single percentage applies to everyone treated.

Symptoms are often more noticeable while the dose is going up and tend to ease over time. Not everyone gets them, and Mounjaro is not behind every new symptom. Infections, other medicines, gallstones and unrelated illness remain possible causes.

Plan for mild symptoms too

For manageable digestive effects, try smaller meals, eat more slowly and avoid foods that clearly make things worse. Keep drinks to hand and talk to a pharmacist or prescriber about problems that persist. Do not keep cutting foods out of your diet without support, especially if eating already feels hard.

A clinician decides whether to delay a planned dose increase or review your treatment. Putting up with side effects is no condition of losing weight. Do not stop diabetes medicines on your own while you work out which treatment caused a symptom.

Get urgent help for severe abdominal pain

Severe pain that does not go away, especially pain spreading to your back, may be pancreatitis and needs immediate medical attention. Vomiting sometimes comes with it, but severe persistent pain without vomiting still needs checking. Do not take another Mounjaro dose while doctors assess suspected pancreatitis.

Gallbladder problems also cause significant abdominal pain, sometimes with fever or yellowing of the skin or eyes. Calling the pain indigestion at home will not tell these conditions apart. Sudden severe pain or a marked turn for the worse needs emergency assessment.

Other warning signs

Difficulty breathing, swelling of the face or throat, or collapsing may mean a serious allergic reaction. Call 999. Repeated vomiting, being unable to keep fluids down, passing much less urine, confusion or severe dizziness point to dehydration or another serious problem and need prompt help.

Low blood sugar matters most when tirzepatide is taken with insulin or a sulphonylurea. Follow your agreed diabetes plan. Get emergency help if someone is unconscious or cannot swallow safely, and never give food or drink to an unconscious person.

Record symptoms to help your clinician

Note when the symptom started, how it relates to injection days or dose increases, your other medicines and what it stops you doing. This helps your clinician tell a short-lived effect from a problem needing tests or a different treatment. With urgent symptoms, get help first and leave the diary for later.

Report suspected side effects through the MHRA Yellow Card scheme. A report feeds into safety monitoring without proving the medicine caused the problem. Stories online cannot show how often a side effect happens, but your own symptoms still deserve a proper assessment.

Sources

Your own medicine leaflet and prescriber come first. A source from another country does not mean the same rule applies in the UK.

  1. Mounjaro UK Summary of Product Characteristics, updated September 2026 medicines.org.uk
  2. Mounjaro UK patient information leaflet medicines.org.uk
  3. NHS: tirzepatide nhs.uk
  4. MHRA: GLP-1 medicines, what you need to know gov.uk
  5. NHS: dehydration nhs.uk
  6. NHS: low blood sugar nhs.uk

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