Dark green poop is almost always caused by something you ate, a supplement you’re taking, or food moving through your gut faster than usual. It’s rarely a sign of anything serious. The color comes down to bile, a yellow-green digestive fluid your liver produces to break down fats. Normally, bile changes from green to brown as it travels through your intestines. When that process gets interrupted or overwhelmed by green pigments in your diet, the result shows up in the toilet.
How Bile Determines Stool Color
Your liver continuously releases bile into your small intestine. As bile moves through the digestive tract, enzymes chemically alter it, gradually shifting its color from yellow-green to the familiar brown you’re used to seeing. This transformation takes time. If food passes through your large intestine too quickly, bile doesn’t fully break down, and your stool retains that green tint.
This is why diarrhea and green stool often go together. Anything that speeds up your digestion (a stomach bug, food intolerance, stress, even a strong cup of coffee on an empty stomach) can push things through before bile completes its color change. The faster the transit, the greener the result.
Foods That Turn Stool Dark Green
The most common culprit is chlorophyll, the pigment that makes plants green. If you’ve been eating large amounts of spinach, kale, or broccoli, you’re loading your digestive system with more green pigment than it can neutralize. Avocados, fresh herbs, pistachios, and matcha (powdered green tea) all carry enough chlorophyll to do the same thing.
Blue and purple foods can also produce dark green stool, which catches people off guard. Blueberries and blackberries mix with yellow-green bile during digestion, and the combination can look dark green or even nearly black if you’ve eaten enough of them. Artificial food coloring works similarly. Brightly dyed frosting, candy, fruit snacks, and freeze pops can tint your stool unexpected colors. If you eat a mix of colored candies, the dyes can blend together and produce dark green or black results.
Think back over the last 24 to 48 hours. If anything on that list was part of a recent meal, you’ve likely found your answer.
Iron Supplements and Medications
Iron supplements are one of the most reliable causes of dark green (sometimes nearly black) stool. Your body only absorbs a portion of the iron in each pill, and the unabsorbed iron oxidizes as it passes through, darkening your stool significantly. This is completely normal and expected while you’re taking iron. It doesn’t mean the supplement isn’t working.
Chlorophyll supplements, which have become popular as “internal deodorants” and detox products, do the same thing for obvious reasons. Antibiotics can also cause green stool by disrupting the balance of gut bacteria that help process bile. If your stool color changed shortly after starting a new medication, that’s likely the connection.
Stomach Bugs and Fast Transit
When a viral or bacterial infection hits your gut, your intestines push contents through rapidly to flush out the invader. This speed means bile stays green instead of converting to brown. If your dark green stool came with sudden diarrhea, nausea, cramping, or a low fever, a stomach bug is the probable cause.
Most of these infections clear on their own within a few days. The green color will fade back to brown once your digestion returns to its normal pace. Staying hydrated matters more than worrying about the color during a bout of gastroenteritis.
Dark Green Stool in Babies
Green stool in infants has its own set of causes that are worth knowing if you’re a parent. Breastfed babies can produce green stool if they aren’t finishing a full feeding on one side. The milk that comes later in a feeding has a higher fat content, and missing it can change how the milk is digested. Babies on protein hydrolysate formula (the kind prescribed for milk or soy allergies) also commonly have green stool. Breastfed newborns who haven’t yet developed a full set of gut bacteria may see green stool as well. In most cases, it’s a normal variation and not a reason for concern on its own.
When the Color Matters More
An isolated episode of dark green stool with no other symptoms is almost never a problem. It typically resolves within a day or two once the food, supplement, or bug clears your system.
Pay closer attention if dark green stool persists for more than a few days without an obvious dietary explanation, or if it comes alongside symptoms like persistent diarrhea, fever, significant abdominal pain, or blood in the stool. Very dark stool that looks black and tarry (rather than green) can sometimes indicate bleeding higher in the digestive tract, which is a different situation entirely. If you’re unsure whether what you’re seeing is very dark green or black, smearing a small amount on white toilet paper can help you distinguish the two colors more clearly.