Black stool is most often caused by something you ate, drank, or swallowed as a supplement. Iron pills, bismuth-based medications like Pepto-Bismol, activated charcoal, black licorice, blueberries, and blood sausage can all turn your poop noticeably dark or black. Less commonly, black stool signals bleeding somewhere in your upper digestive tract, which looks and smells distinctly different. Knowing which type you’re dealing with matters.
Foods and Drinks That Turn Stool Black
Several everyday foods darken stool enough to be alarming if you’re not expecting it. Blueberries, black licorice, and blood sausage are the most common culprits. The dark pigments in these foods pass through your digestive system largely intact and stain your stool on the way out. The color change typically starts within a day or two of eating the food and clears up once you stop.
The key detail: stool darkened by food looks black but keeps a normal texture and doesn’t have an unusual smell. It’s firm or soft the way your stool normally is, not sticky or tar-like.
Medications and Supplements
Iron supplements are one of the most common reasons for unexpectedly black stool. The color comes from unabsorbed iron passing through your gut. Research on dosing thresholds found that black stools didn’t occur at supplemental iron intakes of 20 to 25 mg per day (on top of a normal dietary intake of about 15 mg), but higher doses reliably produce the effect. Most over-the-counter iron supplements contain 45 to 65 mg of elemental iron per tablet, well above that threshold, so black stool while taking iron pills is expected and harmless.
Bismuth, the active ingredient in Pepto-Bismol and similar stomach remedies, causes a different kind of darkening. When bismuth meets the small amounts of sulfur naturally present in your saliva and digestive system, they combine to form bismuth sulfide, a black compound. This can turn both your tongue and your stool black. The effect is temporary and stops once the medication clears your system. Activated charcoal, used for gas or as a detox supplement, also turns stool jet black for the same straightforward reason: you’re swallowing a black substance.
When Black Stool Means Bleeding
Black stool caused by bleeding in the upper digestive tract, from the esophagus, stomach, or the first part of the small intestine, has a medical name: melena. It looks and feels very different from food-stained stool, and recognizing the difference can be genuinely important.
Melena is jet black with a tarry, sticky consistency. It clings to the toilet bowl and is difficult to flush. Most distinctively, it has a strong, foul odor that’s noticeably different from normal stool. That smell comes from blood being broken down by stomach acid and digestive enzymes as it travels through your gut. The longer the blood has been in transit, the darker and more pungent it becomes. Stool that’s simply stained black by food or supplements won’t have this sticky texture or distinctive smell.
As little as 50 to 100 mL of blood loss in the upper digestive tract, roughly a quarter cup, is enough to produce melena. Common causes include peptic ulcers, inflammation of the stomach lining, and tears in the esophagus. Heavy use of anti-inflammatory painkillers like ibuprofen or aspirin increases the risk of these conditions.
Symptoms That Need Urgent Attention
If your black stool is tarry and foul-smelling and you haven’t recently taken iron, bismuth, or activated charcoal, that alone is a reason to get medical attention. Upper GI bleeding stops on its own in about 80% of cases, but the remaining 20% need treatment, and there’s no way to tell which category you fall into without evaluation.
Certain accompanying symptoms point to more significant blood loss and need prompt or emergency care:
- Lightheadedness, dizziness, or fainting
- Unusual fatigue or shortness of breath
- Abdominal cramping or pain
- Vomiting blood or material that looks like coffee grounds
Signs of shock, including confusion, rapid heart rate, pale skin, cold hands and feet, and heavy sweating, mean severe blood loss and require emergency help immediately.
What Happens During Evaluation
If a doctor suspects your black stool comes from bleeding rather than diet, the first step is usually blood work, including a complete blood count to check for anemia and tests to see how well your blood clots. A stool test can detect hidden blood that isn’t visible to the eye, which helps confirm or rule out bleeding.
The most direct way to find the source is an upper endoscopy, where a thin, flexible tube with a camera is guided down your throat to examine the esophagus, stomach, and upper small intestine. This is both a diagnostic tool and a treatment tool: if a bleeding ulcer or tear is found, it can often be treated during the same procedure. If the upper tract looks normal, a colonoscopy or capsule endoscopy (swallowing a pill-sized camera) may be used to look further along the digestive system.
A Quick Way to Check at Home
Before you worry, run through a mental checklist. Have you taken iron supplements, Pepto-Bismol, or activated charcoal in the last day or two? Eaten blueberries, black licorice, or very dark foods? If yes, that’s almost certainly your answer. Stop the food or supplement and your stool color should return to normal within a couple of days.
If you can’t trace the color to anything you’ve consumed, pay attention to the texture and smell. Normal-textured dark stool without an unusual odor is rarely concerning. Sticky, tar-like stool with a distinctly foul smell is the combination that warrants a call to your doctor, especially if it happens more than once or comes with any of the symptoms listed above.