Dark or black poop is usually caused by something you ate, drank, or took as a supplement. Black licorice, blueberries, iron pills, and bismuth-based medications like Pepto-Bismol are the most common culprits. Less often, very dark stool signals bleeding in the upper digestive tract, which needs medical attention. The key is knowing how to tell the difference.
Foods and Drinks That Darken Stool
Several everyday foods can turn your stool noticeably darker. Blueberries, black licorice, and blood sausage are well-known causes. Beets can shift stool toward a dark reddish hue that sometimes looks almost black. Dark chocolate in large amounts and foods with dark artificial coloring can have a similar effect.
This type of color change is harmless and temporary. Once the food clears your system, typically within a day or two, your stool returns to its usual brown. The important thing to know: food-related dark stool looks and smells normal. It doesn’t have an unusually foul odor, and its texture stays the same as your typical bowel movement.
Medications and Supplements
Iron supplements are one of the most common non-food causes of dark stool. Iron oxidizes as it moves through your digestive system, turning stool a matte black or dark green. The color can look alarming, but the texture stays dry and coarse, and it smells like normal stool. If you recently started an iron supplement and your stool turned dark, that’s almost certainly the explanation.
Bismuth, the active ingredient in Pepto-Bismol, causes a similar effect through a different mechanism. When bismuth mixes with trace amounts of sulfur in your saliva and digestive tract, it forms a black compound called bismuth sulfide. This darkens both your stool and sometimes your tongue. The effect lingers for several days after your last dose, which catches some people off guard. Activated charcoal supplements also turn stool black and are equally harmless.
When Dark Stool Means Bleeding
Bleeding in the esophagus, stomach, or upper small intestine produces a specific type of black stool called melena. As blood travels through the digestive tract, stomach acid and digestive enzymes break it down, turning it dark. By the time it reaches your stool, the blood has been fully digested, giving it a distinct appearance that’s quite different from food-stained stool.
The most common cause of this type of bleeding is a peptic ulcer. Ulcers develop when the protective lining of the stomach or upper intestine breaks down, often from long-term use of anti-inflammatory painkillers (like ibuprofen or aspirin) or from an infection with a bacterium called H. pylori. Other possible sources include tears in the esophageal lining, inflamed stomach tissue, or in rarer cases, tumors.
How to Tell the Difference
The physical characteristics of your stool are the most reliable way to distinguish a harmless color change from something that needs attention.
- Color and sheen: Melena is jet black with a glossy, almost shiny surface. Stool darkened by food or supplements looks matte black or dark green without that wet-looking sheen.
- Texture: Melena is sticky and tar-like, clinging to the toilet bowl and difficult to flush. Iron or food-related dark stool has a normal, formed consistency.
- Smell: This is often the most telling sign. Digested blood produces a distinctly foul, metallic odor that’s noticeably different from the usual smell of stool. Food or supplement-darkened stool smells normal.
- Duration: If the color change lines up with something you ate or a medication you started, and it resolves within a couple of days, bleeding is unlikely.
A small amount of upper GI bleeding can sometimes produce stool that looks more dark brown than jet black, making it harder to identify visually. In those cases, the sticky consistency and strong odor are more helpful clues.
Symptoms That Signal an Emergency
Black, tarry stool on its own warrants a call to your doctor. But when it’s paired with other symptoms, the situation may be more urgent. Lightheadedness, dizziness when standing, a racing heartbeat, vomiting blood or material that looks like coffee grounds, severe abdominal pain, or feeling faint are all signs of significant blood loss. Severe bleeding can cause a dangerous drop in blood pressure, and in those cases, emergency care is necessary.
If you’re taking blood thinners or antiplatelet medications and notice black, tarry stool, that combination raises the risk of serious hemorrhage and should be evaluated quickly.
What Happens During Evaluation
When a doctor suspects upper GI bleeding, the standard next step is an endoscopy, a procedure where a thin, flexible camera is passed through the mouth to visually inspect the esophagus, stomach, and upper intestine. Current guidelines recommend this be done within 24 hours for suspected upper GI bleeding. The procedure both identifies the source of bleeding and, in many cases, allows the doctor to stop it during the same session.
If the cause is less clear, your doctor may order a stool test that detects hidden blood. Newer versions of this test (called FIT) are not affected by what you’ve eaten, unlike older versions that could produce false positives from foods like broccoli, cantaloupe, or carrots. About 8% of patients tested with the older method had likely false-positive results due to diet.
A Simple Rule of Thumb
Think back 24 to 48 hours. If you ate blueberries, took Pepto-Bismol, or started an iron supplement, your dark stool is almost certainly explained. If you can’t identify an obvious dietary or medication cause, or if the stool is sticky, tar-like, and unusually foul-smelling, that pattern points toward bleeding that should be evaluated by a doctor.