Mounjaro and Diarrhoea: What Happens and How to Track It

Both tirzepatide (Mounjaro) and semaglutide (Wegovy) act on GLP-1 receptors involved in appetite regulation and digestion. One of the ways GLP-1 receptor agonists work is by slowing the rate at which the stomach empties — and this effect on the digestive system can sometimes tip in the other direction, leading to loose stools or diarrhoea rather than constipation. The two can even alternate in some people.

When is it most likely to happen?

Loose stools and diarrhoea are most commonly reported in the first few days after starting the medicine or after a dose increase. According to information published on the electronic Medicines Compendium (eMC), gastrointestinal effects including diarrhoea are among the commonly listed side effects for tirzepatide. The pattern for semaglutide (Wegovy) is similar — nausea and diarrhoea together are frequently reported, particularly early on.

Does it ease over time?

Many people find that gastrointestinal symptoms, including diarrhoea, become less frequent as their body adjusts to the medicine. This is not universal, however — some people continue to notice it after eating certain foods, eating too quickly, or eating larger portions than their reduced appetite can comfortably handle. Keeping a symptom log is the most reliable way to spot your own personal triggers and patterns. You can read more about the full range of gut-related experiences in our overview of Mounjaro side effects, or explore the specific overlap between sulphur burps and diarrhoea on Mounjaro, which some people notice together.

When should you be concerned?

Occasional loose stools are common and usually not a cause for alarm. However, if diarrhoea is severe, persists for more than a few days, is accompanied by significant pain, blood in the stool, or signs of dehydration, contact your healthcare professional promptly. These symptoms should never be left unaddressed.

One of the most useful things you can do when managing side effects is build a clear picture of what is actually happening — when symptoms occur, how long they last, and whether anything (food, activity, sleep) seems to make them better or worse. That is exactly what GLP Trackr's side-effect tracker is designed for.

Log each episode of diarrhoea — or any gut symptom including loose stools and related digestive discomfort — directly in the app. Over time, the insights feature surfaces patterns in your own data: is it worse on the day after your injection? Does it correlate with particular foods or lower protein intake? These are the kinds of observations that turn a frustrating symptom into something you can discuss meaningfully with your prescriber.

You can also use the food logging feature — including the AI photo scan — to note what you ate before symptoms appeared, which can help identify any dietary triggers worth mentioning at your next appointment. For a closer look at how diarrhoea specifically shows up during treatment, see our detailed guide to diarrhoea on Mounjaro.

GLP Trackr also lets you generate a summary you can bring to a prescriber appointment — so instead of trying to recall how often symptoms happened over the past few weeks, you have a clear, dated record ready to share.

Remember: GLP Trackr helps you observe and record what is happening so you can discuss it with your prescriber — it is not a substitute for their guidance. If your symptoms are severe or persistent, reach out to your healthcare professional rather than waiting for your next scheduled appointment. Any decisions about your dose or treatment should always be made with your prescriber.

Ready to start building a clearer picture of your side-effect patterns? Download GLP Trackr on the App Store or Google Play and start your free 7-day trial — your symptom history could make your next prescriber conversation a lot more informed.