Dark stool is usually caused by something you ate, drank, or took as a supplement. The most common culprits are iron supplements, bismuth-based medications like Pepto-Bismol, and certain dark-colored foods. In less common cases, very dark or black stool signals bleeding in the upper digestive tract, which needs prompt medical attention.
Foods and Drinks That Darken Stool
Several everyday foods can turn your stool noticeably darker, sometimes almost black. The biggest offenders include blueberries, black licorice, and blood sausage. Dark leafy greens, chocolate cookies with dark food dye, and foods with heavy artificial coloring can also shift things toward a much darker shade than you’re used to.
This kind of color change is harmless. Once the food clears your system, your stool should return to its normal brown within a day or two. If you recently ate any of these foods, that’s likely your answer. Think back over the last 24 to 48 hours before you noticed the change.
Medications and Supplements
Iron supplements are one of the most reliable ways to turn stool dark green or black. If you recently started taking iron for anemia or as part of a prenatal vitamin, this is almost certainly the cause. The color change is a normal side effect and doesn’t mean the supplement is harming you.
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and similar stomach remedies, also turns stool black. It happens because bismuth reacts with small amounts of sulfur in your saliva and digestive tract, forming a dark compound. Activated charcoal, sometimes taken for gas or bloating, does the same thing. In all of these cases, your stool color will normalize within a few days of stopping the medication.
When Dark Stool Means Bleeding
If you haven’t taken any of the medications above and can’t trace the color to food, the concern is bleeding somewhere in your upper digestive tract: the esophagus, stomach, or the first section of your small intestine. When blood is exposed to stomach acid and digestive enzymes over several hours, it turns black and sticky by the time it reaches the toilet. This is called melena.
Melena looks and feels different from stool that’s simply dark because of food. It tends to be tar-like in consistency, almost shiny, and has a distinctly foul smell that’s stronger than usual. Stool darkened by blueberries or iron pills, by contrast, has a normal texture and typical odor. That difference in texture and smell is the key distinguishing feature.
Common causes of upper GI bleeding include stomach ulcers, inflammation of the stomach lining, and tears in the esophagus (sometimes from heavy vomiting). Heavy alcohol use and long-term use of anti-inflammatory painkillers both increase the risk of these conditions.
Warning Signs That Need Urgent Attention
Black, tarry stool on its own warrants a call to your doctor. But certain accompanying symptoms mean you should go to urgent care or an emergency room rather than waiting for an appointment:
- Vomiting blood or vomit that looks like dark coffee grounds
- Dizziness, weakness, or lightheadedness, which can signal significant blood loss
- Heart palpitations or shortness of breath
- Several consecutive days of black, tarry stool
These symptoms together suggest active bleeding that your body is struggling to compensate for. Even without those red flags, if your stool doesn’t return to brown within a few days and you can’t identify a dietary or medication cause, it’s worth getting checked out.
Dark Stool in Babies
Newborns pass greenish-black, tar-like stool called meconium during their first few days of life. This is completely normal. It’s made up of everything the baby swallowed in the womb: amniotic fluid, mucus, bile, and shed cells. It clears within the first two to three days.
After that initial period, black stool in a baby is not expected and could indicate blood in the gastrointestinal tract. Dark green stool, on the other hand, is common in babies taking iron-fortified formula or iron drops. That deep pine-green color looks alarming but is harmless and has no effect on the baby’s health.
How to Figure Out Your Cause
Start with the simplest explanation. Run through this quick mental checklist: Have you taken Pepto-Bismol, iron supplements, or activated charcoal in the last couple of days? Have you eaten blueberries, black licorice, or foods with dark dyes? If yes, stop the food or supplement and wait two to three days. Your stool should return to brown once the substance clears your system.
If you can’t identify a dietary or medication cause, pay attention to texture and smell. Normal-textured dark stool is less concerning than stool that’s sticky, tar-like, and unusually foul-smelling. And if you’re also feeling weak, dizzy, or short of breath, those are signs your body is losing blood internally, and you need medical evaluation quickly.