Green poop is almost always harmless. It typically means that something you ate contained strong pigments, or that food moved through your digestive system faster than usual. In either case, the color change is temporary and resolves on its own within a day or two.
Why Poop Is Normally Brown
Your liver produces bile, a greenish-yellow fluid that helps break down fats in the small intestine. As bile travels through the rest of your digestive tract, bacteria in the large intestine chemically transform it, shifting the pigment from green to yellow to brown. That final brown color comes from a pigment called stercobilin, the end product of bile after it has been fully broken down by gut bacteria over many hours.
On average, food takes about six hours to pass through your stomach and small intestine. Waste then spends another 36 to 48 hours moving through the large intestine, where most of that color transformation happens. When anything disrupts that timeline or overwhelms the system with green pigment, you get green stool.
Fast Transit: The Most Common Cause
When food moves through your intestines faster than normal, bile doesn’t have enough time to complete its chemical breakdown. The pigment stays closer to its original green state instead of converting to brown. This is why diarrhea is often greenish. Anything that speeds up digestion, including a stomach bug, food intolerance, stress, or even a large meal that triggers strong contractions, can produce this effect.
If your green stool is also loose or watery, rapid transit is the likely explanation. Once your digestion returns to its normal pace, the brown color comes back.
Foods That Turn Stool Green
Chlorophyll, the pigment that makes plants green, can color your stool the same way. Eating large amounts of spinach, kale, broccoli, avocados, herbs, or matcha (powdered green tea) adds enough green pigment to visibly tint your stool. Pistachios can do the same thing, thanks to chlorophyll and other plant pigments packed into the nut.
Blueberries are a less obvious culprit. They contain a compound called anthocyanin that can produce shades of green as it passes through your system. And artificial food dyes, like the kind used in brightly frosted cupcakes, candy, or colored drinks, continue tinting whatever they touch even after you swallow them. A single cupcake with vivid green frosting can easily explain a green bowel movement the next day.
Supplements and Medications
Iron supplements are one of the most common supplement-related causes of green stool. They can turn poop dark green or even blackish green, which often catches people off guard. This is a normal chemical reaction between iron and your digestive juices, not a sign of a problem.
Some antibiotics also tint stool green or yellow by disrupting the normal balance of gut bacteria. With fewer bacteria available to break down bile pigments fully, the stool retains more of its greenish hue. A few other prescription medications, including certain anti-inflammatory drugs and some hormonal treatments, list green stool as a documented side effect. If you recently started a new medication and noticed a color change, the two are likely connected.
Green Poop in Babies
Green stool in newborns and infants is especially common and rarely a concern. Almost all babies produce their first stools as meconium, a thick, black, tarry substance that accumulated in their intestines before birth. Within the first few days, as breastfeeding or formula feeding begins, those stools transition to green or yellow with a more liquid consistency.
Breastfed babies typically produce stools in the green-yellow-brown range for as long as they continue nursing. Formula-fed babies have similar colors, often slightly lighter. Occasional bright green stools in babies can mean they’re feeding quickly, getting more of the thinner milk at the start of a feeding, or simply processing milk at a slightly faster pace that day. It’s a normal part of infant digestion.
When Green Stool Signals Something More
A single green bowel movement, or even a few in a row after a big salad or a bout of stomach trouble, is not a red flag. The color itself is not dangerous. What matters more is the pattern and any symptoms that come with it.
Green stool that persists for more than several days without an obvious dietary explanation, or that comes with fever, persistent cramping, or significant changes in frequency, may point to an ongoing infection or digestive issue worth investigating. The colors that do warrant prompt attention are bright red (which can indicate fresh bleeding in the lower digestive tract) and black, tarry stools (which may signal bleeding higher up, such as in the stomach). If you see either of those and haven’t been taking iron supplements or eating foods like beets, that’s worth a same-day call to your doctor.
For green stool specifically, the reassuring reality is that it almost always traces back to something you ate, something you’re taking, or a temporary speed-up in digestion. Once the cause passes, so does the color.