Dark or black poop usually means you ate something with a strong pigment or you’re taking a supplement or medication that changes stool color. Blueberries, black licorice, iron supplements, and bismuth-based medications like Pepto-Bismol are the most common culprits. Less commonly, very dark or black stool signals bleeding somewhere in the upper digestive tract, which needs prompt medical attention.
The key distinction is whether your stool is simply darker than usual or whether it’s jet black, sticky, and tar-like. That difference matters a lot.
Foods and Supplements That Darken Stool
Several everyday foods and supplements can turn your stool noticeably darker, sometimes even black. The most common ones include blueberries, black licorice, blood sausage, dark leafy greens, and beets. These foods contain deep pigments that survive digestion and show up in your stool. The color change is harmless and typically resolves within a day or two after you stop eating the food.
Iron supplements are another very common cause. Oral iron tablets frequently turn stool dark green to black because excess iron that isn’t absorbed oxidizes as it moves through your intestines. If you recently started an iron supplement and noticed darker stool with no other symptoms, that’s almost certainly the explanation. The color change lasts as long as you continue taking the supplement.
Medications That Turn Stool Black
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and Kaopectate, is one of the most well-known medication causes. When bismuth meets the small amounts of sulfur naturally present in your saliva and digestive system, the two combine to form bismuth sulfide, a black compound. This substance coats your stool as it moves through, producing a strikingly dark color. The same reaction can also temporarily blacken your tongue.
This is completely harmless. The black color gradually clears as the medication leaves your system, usually within a few days of your last dose. If you took Pepto-Bismol for an upset stomach and your next bowel movement is black, that’s the explanation.
When Dark Stool Means Bleeding
The more serious cause of black stool is bleeding in the upper part of the digestive tract: the esophagus, stomach, or the first section of the small intestine. When blood is exposed to stomach acid and digestive enzymes over several hours, it turns from red to black. By the time it reaches your stool, it produces a distinctive appearance called melena.
Melena looks different from stool that’s been darkened by food or medication. It’s jet black, has a tar-like sticky consistency, and carries a strong, unusually foul odor. If you smear it on a tissue, it may look almost like motor oil. Stool that’s merely dark brown or greenish-black from food tends to hold its normal shape and consistency.
Common causes of upper digestive bleeding include stomach ulcers (often from overuse of anti-inflammatory painkillers like ibuprofen or from a bacterial infection), inflammation of the stomach lining, tears in the esophagus, and swollen veins in the esophagus related to liver disease. Even a small amount of bleeding, roughly 2 tablespoons, can produce noticeably black stool.
How to Tell the Difference
Start with the simplest question: did you recently eat blueberries, black licorice, or dark-colored foods? Are you taking iron supplements, Pepto-Bismol, or activated charcoal? If yes, and you feel completely fine otherwise, the dark stool is almost certainly from that source. Stop the food or medication and watch whether your stool returns to its normal brown color within one to three days.
Normal stool color ranges across all shades of brown and even green. Bile, the digestive fluid your liver produces, starts out yellow-green and gets chemically altered by enzymes as it travels through your intestines, eventually turning brown. How dark that brown ends up depends on your diet, hydration, and how quickly food moves through your system. A stool that’s simply a darker shade of brown is not the same as a truly black stool.
If the stool is genuinely black and tarry, especially if you haven’t eaten anything that would explain it, take it seriously. And if the dark stool is accompanied by any of these symptoms, seek emergency care:
- Vomiting blood or vomit that looks like coffee grounds
- Dizziness, weakness, or lightheadedness
- Heart palpitations or shortness of breath
- Several consecutive days of black, tarry stool
These symptoms suggest significant blood loss and need urgent evaluation.
What Happens During Evaluation
If you visit a doctor about persistent dark stool, the first step is usually a simple test to check whether there’s hidden blood in your stool. You provide a small sample, and the test can detect blood that isn’t visible to the naked eye. This helps confirm whether the dark color is from bleeding or from something harmless.
If blood is detected, the next step is typically an upper endoscopy, where a thin, flexible camera is passed through your mouth to examine your esophagus, stomach, and upper small intestine. This procedure identifies the source of bleeding and, in many cases, allows the doctor to treat it during the same session. Most people are sedated and don’t feel anything during the procedure itself.
Dark Stool in Context
Stool color varies more than most people realize. Eating a handful of blueberries, taking a Pepto-Bismol tablet, or starting a new iron supplement can all produce a stool dark enough to be alarming if you aren’t expecting it. In the vast majority of cases, that’s all it is.
The texture and your overall symptoms matter more than color alone. A formed, normal-consistency stool that happens to be dark is far less concerning than a loose, sticky, tar-like black stool paired with fatigue or dizziness. When in doubt, stopping any suspect food or medication for two to three days gives you a clear answer. If the color doesn’t return to normal, or if you develop any of the warning signs above, that’s when medical evaluation becomes important.