Dark green poop is almost always harmless. It typically means you’ve eaten a lot of green vegetables, taken an iron supplement, or your food moved through your intestines faster than usual. In most cases, your stool color will return to brown within a day or two without any action on your part.
Why Poop Is Normally Brown
Your liver produces bile, a yellow-green fluid that helps digest fats. As bile travels through your intestines, bacteria chemically break it down through a series of reactions that gradually shift its color from green to brown. The end product of that process, called stercobilin, is what gives stool its characteristic brown shade. Anything that disrupts this conversion, whether it’s speed, diet, or medication, can leave your stool looking green instead.
Foods That Turn Stool Dark Green
The most common reason for dark green poop is simply eating a lot of green foods. Spinach, kale, and broccoli are the usual culprits, but avocados, fresh herbs, and matcha (powdered green tea) can do the same thing. These foods are loaded with chlorophyll, the pigment that makes plants green, and your body doesn’t fully break it down during digestion. Pistachios get their green color from the same pigment and can contribute as well.
Blueberries are a less obvious cause. In large quantities, they can produce stool so dark it looks almost black, and shades of deep green aren’t unusual either. Artificial food coloring is another one to watch for. Brightly frosted cupcakes, green sports drinks, or candies with heavy dye loads continue tinting whatever they touch as they pass through your digestive system. If you ate something with vivid coloring in the last day or two, that’s likely your answer.
Iron Supplements and Medications
Iron supplements are one of the most reliable stool color changers. They commonly turn poop dark green or even black. This is a normal side effect of oral iron and not a sign of internal bleeding, though the color can look alarming if you’re not expecting it. The change usually starts within a day or two of beginning the supplement and persists as long as you keep taking it.
Certain antibiotics can also shift stool color toward green or yellow-green. This happens partly because antibiotics alter the gut bacteria responsible for converting bile pigments to brown. If you’ve recently started a course of antibiotics and notice a color change, the medication is the most likely explanation.
Fast Transit Time
When food moves through your large intestine too quickly, bile doesn’t have enough time to complete its chemical transformation from green to brown. The result is green stool, often on the darker side. This is one of the most common explanations when green poop appears alongside diarrhea or loose stools.
Normal transit through the colon alone takes anywhere from 10 to 59 hours, with total gut transit ranging from 10 to 73 hours. That’s a wide window. When something speeds up that process, whether it’s a stomach bug, food intolerance, stress, or even a large cup of coffee on an empty stomach, bile exits before bacteria finish their work. The faster the transit, the greener the result.
Infections and Digestive Conditions
Some bacterial and parasitic infections cause green diarrhea. Salmonella is a well-known example. In these cases, the green color comes from the same mechanism (rapid transit preventing bile breakdown), but the underlying cause is an infection rather than something you ate. You’ll typically have other symptoms too: cramping, fever, nausea, or watery stools that persist for several days.
Conditions that affect fat absorption, like celiac disease, can also change stool appearance, though they more commonly produce yellow, greasy, foul-smelling stools rather than dark green ones. A bile duct blockage, on the other hand, produces the opposite problem: pale, clay-colored stool from a lack of bile reaching the intestines. If your stool is consistently very light rather than green, that’s a more urgent concern.
Green Stool in Babies
Newborns pass meconium, a thick, dark green-to-black substance, within the first 24 to 48 hours after birth. This is completely normal and clears as the baby begins drinking colostrum or formula. After that initial transition, occasional green stools in infants can result from a foremilk/hindmilk imbalance during breastfeeding, formula composition, or simply a fast digestive system that’s still maturing. Green poop in babies is rarely a concern on its own unless it’s accompanied by fussiness, poor feeding, or signs of dehydration.
When Green Stool Signals a Problem
A single episode of dark green poop, or even a few days of it after a big salad or starting iron supplements, is not something to worry about. The Mayo Clinic recommends contacting a healthcare provider if green stool persists for more than a few days without an obvious dietary explanation.
Pay closer attention if green stool comes with diarrhea that lasts more than two days, fever, significant abdominal pain, or signs of dehydration like dark urine, dizziness, or dry mouth. Green stool paired with diarrhea increases your risk of fluid loss, so staying hydrated matters. In the absence of these warning signs, the color change is almost certainly dietary or related to a supplement, and your stool will return to its usual shade once the cause passes through your system.