How to read this guide
Side effects in the UK Summary of Product Characteristics (SmPC) are categorised by frequency: very common (more than 1 in 10 patients), common (1 in 10 to 1 in 100), uncommon (1 in 100 to 1 in 1000), and rare (1 in 1000 to 1 in 10 000). The list below is summarised. The full and authoritative list is in the SmPC and the Patient Information Leaflet supplied with every pen.
Very common side effects
- Nausea
- Diarrhoea
- Vomiting
- Constipation
- Reduced appetite
These are mostly mild to moderate and most pronounced during the first weeks at each new dose. Practical management: eat smaller and more frequent meals, hydrate steadily through the day, avoid alcohol and very rich foods, and time your dose so any peak nausea coincides with sleep.
Common side effects
- Abdominal pain
- Indigestion, reflux, bloating, belching, flatulence
- Fatigue
- Injection-site reactions (redness, itching)
- Dizziness
- Headache
- Hair loss (uncommonly reported)
- Hypoglycaemia — particularly when combined with insulin or sulfonylureas in patients with type 2 diabetes
- Heart rate increase of around 1–3 beats per minute on average
Less common but serious — seek urgent medical advice
These effects are uncommon, but each is potentially serious. If you experience any of them, stop the medicine and contact 111, your GP, or A&E depending on severity.
- Acute pancreatitis — severe, persistent upper abdominal pain that may radiate to the back, often with nausea or vomiting. Treat as an emergency.
- Severe allergic reaction (anaphylaxis) — swelling of the face, lips, tongue or throat; difficulty breathing; severe rash. Call 999.
- Gallbladder problems — including gallstones and inflammation of the gallbladder. Symptoms: pain in the upper right abdomen, jaundice, pale stools.
- Severe dehydration — from persistent vomiting or diarrhoea. In severe cases this can affect kidney function.
- Worsening of diabetic retinopathy — in patients with type 2 diabetes. Any new visual change should be assessed.
- Suicidal thoughts or worsening mental health — a regulatory review is ongoing for GLP-1-based medicines. Any new or worsening mental health symptom should prompt contact with your GP or 111.
Reporting side effects
Suspected side effects should be reported to the MHRA via the Yellow Card scheme. Reporting helps the MHRA monitor the ongoing safety profile of the medicine. Reports can be made by patients, carers, or healthcare professionals.
When to stop the medicine and contact your prescriber
- Any symptom of a serious adverse effect listed above.
- Persistent vomiting or diarrhoea preventing fluid intake.
- Sudden or severe abdominal pain.
- Signs of pregnancy.
- Any side effect that is not settling after the first two weeks at a given dose.
Sources: eMC SmPC for Mounjaro; BNF tirzepatide monograph; NHS — About tirzepatide; MHRA Drug Safety Update on GLP-1 receptor agonists.