Dark green poop is almost always harmless. In most cases, it’s caused by something you ate, a supplement you’re taking, or simply how fast food moved through your digestive system. It rarely signals a serious problem on its own.
Why Poop Turns Green in the First Place
Your liver produces bile, a yellow-green fluid that helps digest fats. As bile travels through your intestines, bacteria break it down and gradually change its color from green to yellow to brown. That familiar brown color is the end result of a full trip through your digestive tract. When something shortens that journey or adds its own pigment, the green shows through.
Foods That Cause Dark Green Stool
The most common culprit is chlorophyll, the pigment that makes plants green. Spinach, kale, broccoli, avocados, herbs, and matcha (powdered green tea) all contain enough chlorophyll to visibly tint your stool. Even pistachios get their green color from chlorophyll and can contribute. The more of these foods you eat in a sitting, the darker green the result.
Blueberries are a less obvious cause. In large quantities, they can turn stool so dark it looks almost black, but shades of dark green are common too. Artificial food coloring in frosted cupcakes, candy, or brightly colored drinks can also pass through your system and change stool color. When multiple dye colors mix together, the result can look dark green or even black.
If you can trace your green stool back to a meal heavy in greens, berries, or colorful processed foods, that’s your answer. The color change is temporary and will resolve once those foods clear your system, typically within a day or two.
Iron Supplements and Medications
Iron supplements are one of the most reliable causes of dark green (sometimes nearly black) stool. This color change is so expected that some physicians actually consider it a sign the supplement is being absorbed properly. If the color bothers you, your doctor can adjust the dose, but it’s not a sign of harm.
Certain antibiotics can also shift stool color toward green or yellow by disrupting the balance of gut bacteria that normally finish converting bile to brown. This effect usually resolves once you complete the course of antibiotics and your gut bacteria repopulate.
Rapid Digestion and Diarrhea
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 green color. This is why diarrhea from a stomach bug, food intolerance, or even stress often comes out green. You haven’t eaten anything unusual; the color is simply unprocessed bile.
A single episode of green diarrhea after something disagreed with you is nothing to worry about. If the diarrhea itself persists for more than a couple of days, the concern shifts from the color to the diarrhea and what’s causing it, whether that’s an infection, a food sensitivity, or something else.
Green Stool in Babies
Green poop in infants has its own set of causes and tends to alarm new parents more than it should. Breastfed babies may produce green stool if they don’t finish feeding on one side. This means they get more of the thinner, lower-fat milk at the start of feeding and miss the fattier milk that comes later, which changes how the milk is digested. Babies on protein hydrolysate formula (used for milk or soy allergies) also commonly have green stool. So do breastfed newborns whose guts haven’t yet been colonized by the bacteria that turn bile brown.
In all of these cases, green stool in an otherwise happy, feeding, gaining-weight baby is normal.
When Green Stool Is Worth Attention
The color itself is rarely the problem. What matters is context. A single green bowel movement with no other symptoms is almost never a concern. But green stool paired with certain other signs can point to an infection, inflammation, or another issue worth investigating.
Pay attention if green stool comes with:
- Severe abdominal pain or cramping that goes beyond mild discomfort
- Fever
- Blood in the stool or stool that looks jet black and tarry (not the dark green-black of iron supplements)
- Persistent diarrhea lasting more than a few days
- Signs of dehydration like dark urine, dizziness, or dry mouth
- Unexplained weight loss
A lasting change in stool color that you can’t connect to your diet, a supplement, or a medication is also worth mentioning to your doctor. “Lasting” generally means weeks, not days. One green bowel movement after a big salad is the system working exactly as expected.
How to Tell What’s Causing Yours
Start with the simplest explanation. Think back over the last 24 to 48 hours. Did you eat a large serving of leafy greens, blueberries, or anything with bright food coloring? Are you taking iron supplements or antibiotics? Did you recently have a bout of diarrhea? If any of these apply, you’ve likely found your cause.
If the green color persists for more than a few days after you’ve ruled out diet and supplements, or if it’s accompanied by any of the symptoms listed above, that’s when it makes sense to get a professional opinion. Otherwise, dark green poop is one of those things that looks alarming in the bowl but means very little on its own.