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Mounjaro side effects
About this page. Written by the GLPInfo editorial team with AI assistance from the official sources listed at the end, and approved by the site owner before publication. It has not been reviewed by a named clinician. Published 27 Aug 2026 · last updated 27 Aug 2026 · next scheduled review 27 Nov 2026.
This page is information, not medical advice. It never tells you which medicine, dose or format is right for you: those decisions sit with you and a qualified prescriber. Spotted an error? Tell us and we'll fix it fast.
This page summarises how the patient information leaflet categorises Mounjaro's side effects. It is deliberately unsoftened: the leaflet in your pack is the authority, your prescriber assesses your personal risk, and Report suspected side effects through the MHRA Yellow Card scheme.
Common effects
The leaflet lists nausea, diarrhoea, vomiting and constipation as very common (affecting more than 1 in 10 people), typically worst in the weeks after starting or stepping up a dose and easing as the body adjusts. Commonly reported effects include reduced appetite, abdominal pain, indigestion, burping, wind, reflux, tiredness, injection-site reactions, and low blood sugar in people also taking certain diabetes medicines.
Serious risks
Less common but serious risks in the leaflet include acute pancreatitis, gallbladder problems such as gallstones and inflammation, dehydration from persistent vomiting or diarrhoea (which can strain the kidneys), and allergic reactions. Severe, persistent abdominal pain, with or without vomiting, needs urgent medical attention: do not wait it out.
Worth knowing
Two Mounjaro-specific practical points from the leaflet: it is not for use in pregnancy, and women using oral contraceptives are advised to add a barrier method for four weeks after starting and after each dose increase, because tirzepatide can affect how oral contraceptives are absorbed. Discuss timing with your prescriber if pregnancy is a possibility.
Managing the common effects
Practical, NHS-guidance-level measures for nausea, constipation and dehydration, plus the red flags that mean stop self-managing and call, are collected in one place: managing GLP-1 side effects. Always tell your prescriber what you are experiencing; dose timing and step-ups are their levers, not yours.
Related: what is Mounjaro? · how to take Mounjaro · dose schedule
Frequently asked questions
Do Mounjaro side effects go away?
The common gastrointestinal effects are typically worst after starting or increasing a dose and ease as the body adjusts, which is exactly why doses climb slowly. Effects that are severe, persistent or worrying belong with your prescriber, not with waiting. Practical self-care measures are covered in managing GLP-1 side effects.
When should I seek urgent help?
Severe persistent abdominal pain (with or without vomiting), signs of an allergic reaction such as swelling of the face or throat or difficulty breathing, or signs of serious dehydration all need urgent medical attention: 999 or A&E for the emergencies, NHS 111 when unsure.
Should I report side effects even if they are listed?
Yes. Reporting through the MHRA Yellow Card scheme strengthens the safety picture for everyone, and reporting something does not require certainty that the medicine caused it.