Why Mounjaro Can Cause Diarrhoea — and Other GI Effects
Mounjaro acts on GLP-1 and GIP receptors involved in digestion and appetite regulation. One of its effects is to slow gastric emptying — the rate at which food moves through the stomach and intestines. While this contributes to the sense of fullness many people notice, it can also disrupt normal digestive rhythm, leading to loose stools, diarrhoea, or, for some people, the opposite — constipation.
Beyond diarrhoea, a range of gastrointestinal effects are commonly reported by people taking Mounjaro:
- Wind and bloating — slowed digestion can cause gas to build up, contributing to flatulence and discomfort
- Sulphur burps — an unpleasant side effect some people notice, also linked to slower stomach emptying causing food and gases to linger longer
- Heartburn and indigestion — the lower oesophageal sphincter can be affected, allowing stomach acid to reflux upward
- Nausea — one of the most commonly reported effects overall, often occurring alongside loose stools
Other effects that are less specifically digestive but commonly reported include headaches, fatigue, dry mouth, and dizziness. Some people also notice changes in energy levels — while some report feeling more energetic as their weight and appetite adjust, others experience periods of low energy, particularly in the early stages. These patterns vary considerably from person to person.
According to the electronic Medicines Compendium (eMC), gastrointestinal reactions are among the most frequently reported adverse effects in clinical data for tirzepatide, and are generally most pronounced during the titration period.
For a broader look at what to expect, the Mounjaro side effects overview covers the full range of commonly reported effects. If you are also curious whether similar patterns occur with other GLP-1 medicines, you may find it useful to read about diarrhoea on Wegovy for comparison.
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Tracking Digestive Side Effects with GLP Trackr
One of the most practical things you can do when navigating gastrointestinal symptoms is to keep a consistent log — not to self-diagnose, but to spot patterns and bring useful information to your prescriber. GLP Trackr's side-effect tracking feature lets you record symptoms like diarrhoea, wind, heartburn, and sulphur burps each day, so you can see whether they cluster around injection day, ease after a few days, or persist beyond what is typical.
Over time, the app builds a picture of your individual pattern — for example, whether symptoms tend to peak on day one or two after your weekly dose, or whether certain foods appear to make things worse. This kind of personal data is genuinely useful when you sit down with your prescriber to review how the medicine is suiting you.
The more detailed look at Mounjaro and diarrhoea explores what commonly affects severity and duration. If headaches are also something you are noticing, tracking headaches on Mounjaro covers how those patterns often look.
If your diarrhoea is severe, persistent, or accompanied by signs of dehydration, contact your healthcare professional promptly — do not wait for your next scheduled appointment. GLP Trackr is a tracking tool to help you record and reflect on your experience; it is not a substitute for clinical guidance, and any concerns about your symptoms should always be discussed with your prescriber or doctor.
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Frequently asked questions.
Diarrhoea is a commonly reported gastrointestinal side effect of Mounjaro (tirzepatide). It is linked to the medicine's effect on digestion, including slower gastric emptying. It is often most noticeable early in treatment or after a dose increase, and tends to ease for many people as their body adjusts.
Sulphur burps on Mounjaro are thought to result from slower stomach emptying, which causes food and gases to remain in the digestive system longer than usual. This can produce a distinctive sulphur-like odour. The effect is commonly reported and often improves as the body adapts to the medicine.
Wind and bloating are frequently reported by people taking Mounjaro. Slowed gastric emptying can allow gas to build up in the digestive tract. These effects are generally most noticeable during the early weeks or after a dose change and often settle over time.
For many people, digestive side effects like diarrhoea are most prominent in the first few days after starting or increasing the dose, and ease within a week or two. Duration varies between individuals. If diarrhoea is severe, persistent, or causing dehydration, contact your healthcare professional promptly.
Yes — headaches and dry mouth are both commonly reported alongside digestive effects on Mounjaro. These non-gastrointestinal symptoms are noted in clinical data for tirzepatide. Logging all symptoms together in a tracking app can help you identify patterns to discuss with your prescriber.