Green Poop on Mounjaro or Wegovy: What's Going On?

Both Mounjaro (tirzepatide) and Wegovy (semaglutide) act on GLP-1 receptors, which slows how quickly food moves through the digestive tract — an effect known as delayed gastric emptying. Mounjaro also acts on GIP receptors, making its effect on digestion somewhat broader.

Bile, a digestive fluid produced by the liver, starts out yellow-green and normally turns brown as it travels through the intestines. When transit slows significantly, bile has more time to be reabsorbed and the usual colour change can be disrupted. Conversely, if the medicine triggers faster transit on some days — such as loose stools or diarrhoea — bile may not have enough time to break down fully, which also produces a green or dark green appearance.

Other contributing factors

• Diet changes: Many people eat more leafy green vegetables, spinach, or green smoothies on a GLP-1 journey. Chlorophyll from these foods can directly colour stool green.
• Reduced food intake: Eating significantly less overall changes how the digestive system processes waste.
• Iron supplements: If you take iron, this can cause darker, greenish-black stools independently of your medication.

Dark poop on Mounjaro is not always the same as green poop — very dark or black stool can sometimes signal something that needs prompt medical attention. You can read more about dark and black poop on Mounjaro to understand when the colour warrants a call to your healthcare professional.

Gastrointestinal changes like these sit within a broader set of commonly reported experiences on these medicines. If you are curious about what else to expect, the general guide to being on Mounjaro covers the wider picture, and the Mounjaro information hub links out to every topic in one place.

Side-effect tracking is one of the most practical things you can do when changes like this appear. Logging when the change started, how often it occurs, and whether it coincides with a dose day or a food change gives you something concrete to discuss at your next appointment — rather than trying to recall details weeks later.

GLP Trackr's side-effect tracker lets you log exactly this kind of symptom alongside your other daily data — mood, energy, food, and water intake — so you can spot patterns over time. If you notice, for example, that green stools appear consistently in the two days after your weekly injection, that is a useful data point for your prescriber. The app's doctor report feature pulls this logged history together into a clear summary you can bring to an appointment, saving you the guesswork of trying to remember a timeline on the spot.

If you have also noticed changes in your appetite or weight patterns at the same time, it can help to see all of that in context. Some people find that unexpected weight changes on Wegovy connect to broader digestive and dietary shifts — tracking gives you the full picture.

GLP Trackr is available free on the App Store and Google Play, with a 7-day trial to explore the full feature set — including side-effect logging and your personalised doctor report.

When to contact your healthcare professional promptly: if stools are very dark, tarry, or black (which can indicate bleeding), if you have abdominal pain, if changes are severe or have lasted more than a week or two without improvement, or if anything feels unusual — contact your prescriber or doctor. GLP Trackr helps you record what you are experiencing so you can have a more informed conversation; it is not a substitute for clinical advice.