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Mounjaro And Diarrhoea: Managing Gastrointestinal Side Effects Safely

Mounjaro And Diarrhoea: Managing Gastrointestinal Side Effects Safely


Written by:

MedExpress

Medically reviewed by:

Dr Zoë Lees

Published:

21 December 2025

Updated:

6 February 2026

Reading time: 4 minutes
Mounjaro and Diarrhoea

If you’re using Mounjaro for weight loss or you are thinking about starting, it’s helpful to understand side effects and how to manage them.

In this article, we’ll take a closer look at one of the most common digestive side effects, diarrhoea. We’ll walk you through what it is, why it happens and what you can do to manage it.

Article Summary:

  • Mounjaro (tirzepatide) is a once-weekly injection used for weight loss and type 2 diabetes, helping control blood sugar and reduce appetite. It mimics the GLP-1 and GIP hormones to promote weight loss.
  • Diarrhoea is one of the most common digestive side effects of Mounjaro because of how it affects your digestion.
  • Stay hydrated, eat small meals, rest, and take paracetamol for discomfort to manage diarrhoea.

Overview of Mounjaro (tirzepatide)

Mounjaro is a widely used medication for weight loss that contains the active ingredient tirzepatide. It’s administered once a week through a subcutaneous injection, which means it’s injected just under the skin.

Mounjaro belongs to a class of drugs called GIP/GLP-1 receptor agonists, which work by mimicking two naturally occurring hormones in your gut that are released after eating.

The hormone, GIP (gastric inhibitory polypeptide), helps your body produce more insulin after meals and may also play a role in how fat is processed.

The other hormone, GLP-1 (glucagon-like peptide-1), supports blood sugar control and appetite regulation. It increases insulin production when blood sugar is high, slows digestion so you feel full longer and signals the brain to reduce hunger. Medications such as Wegovy, Ozempic, and Saxenda mimic the effects of GLP-1 to support weight loss. [1]

Common Gastrointestinal Side Effects

Like all medications, Mounjaro can cause side effects, with some more common than others. The most common side effects of Mounjaro are gastrointestinal, which means they’re related to your digestive system, including nausea, diarrhoea, constipation, vomiting and stomach pain and discomfort. [1]

Diarrhoea is one of the most frequently reported digestive side effects of Mounjaro. While it’s usually mild to moderate, understanding why it happens can help manage it effectively.

Diarrhoea is defined as frequent, loose or watery stools. You might feel sharp or dull discomfort in your stomach, which often gets worse just before you need to go to the bathroom. You may have an urgent need to go to the toilet more than three times a day.

Why Mounjaro Causes Diarrhoea

Firstly, Mounjaro slows how quickly food leaves the stomach. While this can reduce appetite, it also changes how food and liquids move through the intestines. These changes can reduce water absorption, leading to looser stools or diarrhoea.

Mounjaro also affects how your intestines naturally move food through your digestive system. This change in rhythm can sometimes lead to diarrhoea. [1]

Side effects often appear during the early weeks of starting Mounjaro or after a dose increase, as the body adjusts to the medication. For most people, diarrhoea is temporary and improves as your digestive system adapts.

Practical Management Strategies

If you experience diarrhoea while taking Mounjaro, there are several ways to help your body recover and stay comfortable.

  • Drink plenty of fluids such as water or herbal teas to replace what’s lost.
  • Eat small, frequent meals as they are gentler on your digestive system than larger portions.
  • Rest and give your body time to adjust.
  • If your symptoms persist, consider using oral rehydration salts to restore lost fluids and electrolytes. For general discomfort or pain, paracetamol can help.

You should seek medical attention if diarrhoea lasts longer than a week or if you notice blood in your stool. Call 999 immediately if you develop sudden or severe stomach pain, or if you experience a high fever or chills, as these could indicate a more serious condition.

If you’re using oral contraception and experience diarrhoea lasting more than 24 hours, you may need an extra dose of your pill to ensure continued protection against pregnancy.

Ready to Start Your Weight Loss Journey?

At MedExpress, we’re here to support you through your whole weight loss journey. If you’re thinking about getting started, find out more by taking a consultation on our website.

References:

  1. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine [Internet]. 2022 Jun 4;387(3):205–16. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2206038

Next scheduled review date: 6 February 2029

Authors

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Written by: MedExpress

MedExpress

Dr Zoë Lees

Medically reviewed by: Dr Zoë Lees

Dr Zoe Lees is a medical writer with postdoctoral research experience from the University of Glasgow, where she focused on metabolic complications of pregnancy and the role of adipose tissue (fat tissue) function. Zoe has a specialist interest in medical communications and is dedicated to delivering content of the highest scientific quality, grounded in robust evidence-based research.

Note from the experts

Remember: This blog shouldn’t be regarded as medical advice, diagnosis, or treatment. We make sure everything we publish is fact checked by clinical experts and regularly reviewed, but it may not always reflect the most recent health guidelines. Always speak to your doctor about any health concerns you have.