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Mounjaro And Diarrhoea: Managing Gastrointestinal Side Effects Safely
Mounjaro And Diarrhoea: Managing Gastrointestinal Side Effects Safely
Dr. Zoë Lees (PhD)
Dr. Sophie Dix (BSc, PhD)
21 December 2025 | Updated: 4 August 2026
4 August 2026
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:
- 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: 4 August 2029
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Authors
Written by: Dr. Zoë Lees (PhD)
Dr. Zoë Lees is a medical writer at MedExpress specialising in obesity and health communication. She completed her PhD at the University of Glasgow, where she investigated adipose tissue (fat tissue) function in pregnancies complicated by pre-eclampsia and gestational diabetes. Her work focuses on translating complex clinical evidence into clear, engaging and evidence-based health information for patients and the public. At MedExpress, Zoë contributes to clinical content, educational resources and media communications across areas including weight management, GLP-1 therapies and metabolic disease. Zoë is particularly interested in improving public understanding of obesity as a chronic condition and ensuring patients have access to accurate, accessible health information grounded in current scientific evidence.
Medically reviewed by: Dr. Sophie Dix (BSc, PhD)
Dr. Sophie Dix is Head of Medical Affairs at MedExpress. A behavioural neuroscientist by training, Sophie has spent 30 years working at the intersection of medical research, pharmacology, technology and patient communication across the pharmaceutical industry, health technology and charity sectors. At MedExpress, Sophie's role is to ensure that everything the organisation does is grounded in the most current science. That means translating complex clinical evidence into accessible health information across the website, clinical pathways and media communications. It also means working with external press and broadcast media as a named expert commentator, making the science behind weight management and GLP-1 treatments understandable to a general audience. A core part of Sophie's work is building MedExpress's Real-World Evidence (RWE) programme: learning systematically from patient outcomes to understand what works in practice, not just in clinical trials. This patient-level insight feeds directly into improving patient experience and health outcomes. Sophie believes that patients make better decisions when they have access to accurate, evidence-based information. As an advocate for meaningful change in how obesity is understood, Sophie works to reduce stigma and raise awareness of the condition as an illness. This includes reframing the conversation around GLP-1s from aesthetics to public health, while highlighting the health benefits of weight loss and weight management.
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.