Dark-colored poop usually means one of two things: something you ate or swallowed changed the color, or there’s bleeding somewhere in your upper digestive tract. The distinction matters because one is harmless and the other can be serious. The quickest way to narrow it down is to think about what you’ve consumed in the last day or two and whether you have any other symptoms.
Why Poop Is Brown in the First Place
Your liver produces bile, a greenish fluid that helps digest fats. As bile travels through your intestines, bacteria break it down into a pigment called stercobilin, which gives stool its characteristic brown color. When something disrupts that process, or when another substance enters the mix, the color shifts. Dark brown poop is perfectly normal. The concern starts when stool turns distinctly black, looks tarry, or has an unusually sticky texture.
Foods and Supplements That Darken Stool
Several everyday foods can turn your poop very dark green or nearly black. Blueberries are a common culprit, especially if you eat a large quantity. Black licorice does the same. Even brightly colored candy, when you eat enough of it, can mix together in your gut and produce black stool.
Iron supplements are another frequent cause. They often turn stool dark green or blackish, which can be alarming if you’re not expecting it. Pepto-Bismol (bismuth subsalicylate) is notorious for this as well. When bismuth meets the small amounts of sulfur naturally present in your saliva and digestive tract, it forms bismuth sulfide, a black compound. The effect is temporary. Your stool color should return to normal within a couple of days after you stop taking it.
If you recently started any of these foods or products and you feel fine otherwise, the dark color is almost certainly harmless.
When Dark Stool Means Bleeding
Black, tarry stool with a sticky consistency and a strong, foul smell is called melena. It looks different from the dark stool caused by food or supplements because it has a distinct tar-like quality. This appearance comes from blood that has traveled through your upper digestive tract, where stomach acid and digestive enzymes break down hemoglobin (the protein in red blood cells) and turn it very dark.
The most common causes of upper digestive bleeding include:
- Peptic ulcers: open sores on the lining of the stomach or the first part of the small intestine. These are frequently caused by a bacterial infection (H. pylori) or regular use of anti-inflammatory pain relievers like ibuprofen, aspirin, or naproxen.
- Gastritis: inflammation of the stomach lining, which can develop shallow breaks that bleed. Alcohol, pain relievers, and H. pylori are the usual triggers.
- Esophagitis: inflammation of the esophagus, often from chronic acid reflux, that can create ulcers and bleeding.
- Esophageal varices: enlarged veins in the esophagus or stomach, most often caused by liver cirrhosis and the high blood pressure it creates in the portal vein. These veins can grow over time and eventually burst, producing significant bleeding.
- Mallory-Weiss tears: small tears in the lower esophagus, typically caused by severe or prolonged vomiting.
Benign growths or cancers in the esophagus or stomach can also weaken the digestive lining enough to expose blood vessels, though these are less common causes.
Warning Signs That Need Urgent Attention
Dark stool on its own, without other symptoms, is worth monitoring but doesn’t always require a trip to the emergency room. What changes the urgency is the combination of black, tarry stool with other signs of significant blood loss. Seek emergency care if you notice:
- Vomiting blood, or vomit that looks like coffee grounds
- Feeling dizzy, weak, or lightheaded
- Heart palpitations or shortness of breath
- Black, tarry stools lasting several days
These symptoms together suggest your body is losing enough blood to affect circulation, which requires prompt evaluation. Even without those red flags, persistent black stool that you can’t trace to food, supplements, or medication warrants a visit to your doctor.
How to Tell the Difference at Home
There’s no perfect at-home test, but a few practical clues help. First, think about timing. If you started iron supplements, ate a pint of blueberries, or took Pepto-Bismol in the last 24 to 48 hours, try stopping and watching whether the color returns to normal within a couple of days. Stool darkened by food or supplements typically looks uniformly dark but maintains a normal consistency. Melena, by contrast, tends to be notably sticky, almost like tar, and has a particularly strong odor that’s different from your usual bowel movements.
Hospital-based stool tests for hidden blood (fecal occult blood tests) are not as reliable as many people assume. A recent quality analysis found that in acute care settings, these tests had a sensitivity of only about 33% for detecting bleeding confirmed by endoscopy, with a false negative rate of over 63%. In other words, a negative result doesn’t rule out bleeding. Doctors rely more on your symptoms, vital signs, and direct examination of the digestive tract when they suspect active bleeding.
NSAIDs and Blood Thinners Raise the Risk
If you regularly take ibuprofen, aspirin, naproxen, or prescription blood thinners, you’re at higher risk for upper digestive bleeding. These medications can erode the protective mucus layer of your stomach and intestinal lining, making ulcers more likely. They also reduce your blood’s ability to clot, so even minor irritation can produce more bleeding than it normally would. People on these medications should pay closer attention to any change in stool color.
Dark Stool in Newborns
If you’re a new parent noticing very dark poop in your baby’s diaper, it’s almost certainly normal. Nearly all newborns pass thick, black, tarry stools called meconium in their first days of life. This is material that accumulated in the baby’s intestines before birth. Once your baby starts breastfeeding or drinking formula, the stool transitions to green or yellow with a more liquid consistency. This shift typically happens within the first few days. Dark stool that reappears after this transition, or stool that contains visible red blood, is worth bringing up with your pediatrician.