Mounjaro side effects: what UK patients report
Real-world side effect data from the MHRA Yellow Card scheme — the UK's official system for reporting suspected adverse reactions.
What UK patients are reporting about Mounjaro
Source: MHRA Yellow Card scheme (November 2023 – December 2025)
Important: Yellow Card reports are suspected reactions — they do not confirm that Mounjaro caused the side effect. Many factors can contribute to symptoms during treatment.
Most commonly reported reactions
Data from the MHRA Interactive Drug Analysis Profile for tirzepatide. Accessed April 2026. Yellow Card reports can be submitted by patients, healthcare professionals, and pharmaceutical companies.
How this compares to clinical trials
In the SURMOUNT clinical trials (the studies that led to Mounjaro's approval for weight management), the most commonly reported side effects were:
Side effects were most common during dose escalation (the first 4–8 weeks) and typically decreased over time. Most gastrointestinal effects were rated mild to moderate.
When to contact your prescriber
- !Severe or persistent abdominal pain (possible pancreatitis)
- !Persistent vomiting that prevents you from keeping food or fluids down
- !Signs of allergic reaction: swelling of face, lips, tongue, or throat
- !Changes in vision (rare, but reported)
- !Symptoms of low blood sugar if taking alongside insulin or sulphonylureas
If you experience any side effects, you can report them directly to the MHRA via the Yellow Card scheme.
Managing common side effects
Nausea
Eat smaller, more frequent meals. Avoid rich, fatty, or spicy foods during dose escalation. Stay hydrated. Most patients find nausea improves after 4–6 weeks.
Constipation
Increase fibre intake gradually. Drink at least 2 litres of water daily. Gentle exercise helps. Your prescriber can recommend laxatives if needed.
Injection site reactions
Rotate injection sites between abdomen, thigh, and upper arm. Allow the pen to reach room temperature before injecting. Apply a cold compress if irritation occurs.
Important disclaimer
This page contains information based on MHRA Yellow Card data and published clinical trial results. It does not constitute medical advice. Do not stop or change your medication without consulting your prescriber. If you experience any side effects, contact your GP, pharmacist, or prescribing clinic. You can also report suspected side effects via the MHRA Yellow Card scheme.