Dark or black poop usually comes from something you ate, drank, or took as a supplement. Foods rich in dark pigments, iron supplements, and stomach remedies like Pepto-Bismol are the most common culprits. Less often, very dark stool signals bleeding in the upper digestive tract, which needs prompt medical attention. The key distinction is whether the color change lines up with something in your diet or came out of nowhere.
Foods That Turn Stool Dark or Black
Several everyday foods contain pigments strong enough to change your stool color dramatically. Blueberries are one of the most common offenders. The pigments in anthocyanin, a compound that gives blueberries their deep color, can tint stool so dark it looks almost black if you eat a large amount. Shades of dark green are possible too.
Black licorice is another well-known cause. The dark dye in the candy passes through your system and can make stool look jet black. Even eating large handfuls of brightly colored candy can do it, because the mixed dyes combine into a dark shade by the time they reach the other end. Other foods that sometimes darken stool include beets (which can also cause a reddish tint that looks alarming), dark leafy greens like spinach, and foods made with dark food coloring.
The timeline is straightforward: stool color typically returns to normal within a day or two after you stop eating the food in question. If you recently binged on blueberries or had a bag of black licorice, that’s almost certainly your answer.
Iron Supplements
Iron supplements are one of the most reliable causes of dark stool. When you take more iron than your intestines can absorb, the excess passes through your digestive tract and turns stool dark green or black. This is purely a cosmetic side effect and not a sign of harm.
The higher the dose, the more likely it is to happen. In studies of pregnant women taking different iron formulations, black stools were reported by about 8% of women taking 25 mg of iron, 22% at 40 mg, and 31% at 50 mg. Most standard iron supplements contain 45 to 65 mg of elemental iron per tablet, so darkened stool is more the norm than the exception for people supplementing iron. Your stool should return to its usual color within a few days of stopping.
Pepto-Bismol and Similar Remedies
Pepto-Bismol and other bismuth-containing stomach medicines can turn stool jet black. The reason is a simple chemical reaction: bismuth, the active ingredient, combines with trace amounts of sulfur in your saliva and digestive system to form bismuth sulfide, a black-colored compound. The same reaction can temporarily darken your tongue.
This effect can last for several days after your last dose, which sometimes catches people off guard. It’s harmless and resolves on its own once the bismuth clears your system. If you recently took a pink stomach remedy and your stool turned black a day or two later, that’s the explanation.
When Dark Stool Signals Bleeding
The cause worth taking seriously is bleeding in the upper digestive tract. When blood is exposed to stomach acid and digestive enzymes, it turns black and takes on a tarry, sticky consistency. This type of stool has a medical name, melena, and it looks and behaves differently from stool that’s simply been darkened by food or supplements.
Melena is black, tarry, and distinctly sticky. Many people who’ve had it remember the unusual texture. It also tends to have a strong, foul smell that’s different from normal stool. The black color comes from blood that originated somewhere in the upper digestive tract: the esophagus, stomach, or the first part of the small intestine. Common causes include stomach ulcers, inflammation of the stomach lining, and enlarged veins in the esophagus.
The location matters because of transit time. Blood from higher up in the digestive tract has time to be broken down, which is what makes it black and tarry. Blood from lower in the colon, by contrast, typically shows up as bright red streaks on or in the stool. One exception: very rapid upper GI bleeding, often from an artery in a peptic ulcer, can move through quickly enough to appear red rather than black.
How to Tell the Difference
The simplest first step is to think back over the last 24 to 48 hours. Did you eat blueberries, black licorice, or dark-colored foods? Are you taking iron supplements or a bismuth-based stomach medicine? If yes, you likely have your answer, especially if you feel completely fine otherwise.
Dark stool from food or supplements is typically just dark in color. It looks and feels like normal stool. Melena from internal bleeding is different in several ways: it’s tarry and sticky, has a particularly strong odor, and usually comes with other symptoms. You might feel dizzy, weak, or lightheaded. Some people notice heart palpitations or shortness of breath, signs that blood loss is affecting circulation. Vomiting blood, or vomit that looks like dark coffee grounds, is another clear red flag.
If you can’t trace the color to anything in your diet and the stool has that tarry, sticky quality, or if you’re experiencing any of those accompanying symptoms, treat it as urgent. Several days of persistently dark, tarry stool without a dietary explanation also warrants prompt evaluation.
What Happens During Evaluation
If your doctor suspects bleeding, one of the first steps is a fecal occult blood test, which checks for hidden blood in the stool. It’s worth knowing that certain foods and supplements can cause false positives on the most common version of this test. You may be asked to avoid rare red meat, certain fruits and vegetables, iron supplements, vitamin C, and common pain relievers like aspirin and ibuprofen for a few days before the test to get an accurate result.
If blood is confirmed, the next step is usually identifying the source. For upper GI bleeding, this often involves a scope passed through the mouth to examine the esophagus and stomach. The goal is to find and treat the cause, whether that’s an ulcer, a tear, or another source of bleeding. Most causes of upper GI bleeding are treatable once identified.
Color Changes That Look Concerning but Aren’t
Dark green stool is common and almost always harmless. It can come from eating large amounts of leafy greens, green-colored foods, or iron supplements. Stool that’s very dark brown is also normal, especially after eating a lot of meat or chocolate. The color of normal stool varies more than most people realize, ranging from light brown to dark brown depending on diet and how long food spent in the digestive tract.
The color to pay attention to is true black with a tarry texture. If your stool is simply darker than usual but otherwise looks and feels normal, and you can connect it to something you consumed, it’s almost certainly nothing to worry about. Stool color from dietary causes returns to normal within one to three days once you stop eating the triggering food or supplement.