Green poop is almost always harmless. It typically means something you ate, drank, or took as a supplement moved through your digestive system faster than usual or contained enough green pigment to override the normal brown color. All shades of brown and even green are considered typical stool colors.
To understand why, it helps to know where the usual brown comes from. Your liver produces bile, a yellow-green fluid that helps digest fats. As bile travels through your intestines, bacteria break it down and it gradually shifts from green to brown. Anything that speeds up that journey or adds extra green pigment can leave your stool looking green.
Foods That Turn Stool Green
The most common cause is simply eating a lot of green vegetables. Spinach, kale, broccoli, avocados, fresh herbs, and matcha are all rich in chlorophyll, the pigment that makes plants green. That pigment doesn’t fully break down during digestion, so it can color your stool bright green, especially if you ate a large serving. Pistachios can do the same thing, since their green color also comes from chlorophyll.
You don’t even need to eat something green. Blueberries can produce greenish stool, and artificial food dyes are a frequent culprit. Brightly colored frosting, candy, sports drinks, or anything with synthetic coloring keeps tinting material as it passes through your gut. If you ate or drank something with vivid coloring in the last day or two, that’s likely your answer.
Medications and Supplements
Iron supplements are a well-known cause. They can darken your stool and give it a green or even blackish-green appearance. This is a normal side effect of the iron itself and not a sign of a problem.
Antibiotics are another common trigger. They disrupt the normal balance of bacteria in your gut, and since those bacteria are responsible for converting bile from green to brown, a temporary shift in their population can leave stool looking green. This usually resolves once you finish the course of antibiotics and your gut bacteria recover.
Rapid Transit Through the Gut
When food moves through your intestines faster than normal, bile doesn’t have enough time to fully break down. The result is stool that retains bile’s original yellow-green color. This is why green stool so often shows up alongside diarrhea, whether from a stomach bug, food intolerance, stress, or anything else that accelerates digestion. The green color in these cases is not the problem itself. It’s just a visible marker that things moved quickly.
Green Stool in Babies
If you’re searching because your baby has green poop, the context matters. Green stool on its own can be completely normal in infants, especially in the first few days of life when dark greenish-black meconium is expected.
In breastfed babies, green, frothy, or explosive stools sometimes point to what’s called lactose overload. Fat in breast milk helps slow down how quickly milk moves through a baby’s gut, giving the body time to digest lactose properly. If a baby gets a high volume of milk or has short feeds, they may not get enough of the fat-rich milk that comes later in a feeding. The lactose doesn’t fully break down, leading to gas, tummy pain, and green runny poop. Dark green stool in small amounts can also mean a baby isn’t getting enough milk overall.
Formula-fed babies may also have greenish stool depending on the formula’s iron content, which is normal.
When Green Stool Signals Something More
In the vast majority of cases, green poop resolves on its own within a day or two once the food, supplement, or illness passes. The Mayo Clinic recommends contacting a healthcare professional if green stool persists for more than a few days without an obvious dietary explanation.
Pay closer attention if green stool comes with other symptoms: persistent diarrhea, fever, cramping, or signs of dehydration like dark urine, dizziness, or dry mouth. Green diarrhea specifically can lead to fluid loss, so staying hydrated is important. Bright red or black stool (not dark green from iron) is a different situation entirely and warrants prompt medical attention, as those colors can indicate bleeding in the digestive tract.
For most people, though, green poop is a one-off event with a boring explanation: you ate a big salad, took an iron pill, or had a cupcake with neon frosting. Once you stop eating the culprit or your digestion returns to its normal pace, the color goes back to brown.