Dark or black stool is usually caused by something you ate, a supplement you’re taking, or an over-the-counter medication. Less commonly, it signals bleeding somewhere in your upper digestive tract. The key to figuring out which one is paying attention to a few telltale details: texture, smell, and what else is going on in your body.
Foods That Turn Stool Dark
Several common foods can darken your stool enough to make it look black or nearly black. Blueberries are one of the most frequent culprits, especially if you eat a large amount. The deep pigment in the fruit can tint stool so dark it looks almost black. Black licorice does the same thing. Even brightly colored candy, if you eat enough of it, can mix colors during digestion and produce a surprisingly dark result.
Beets deserve a special mention because they contain a red pigment called betanin that can make stool look deep red or blood-like, which understandably alarms people. It’s harmless, but it’s one of the most common reasons people panic about their stool color.
If food is the cause, your stool should return to its normal brown color within a day or two of stopping that food.
Medications and Supplements
Iron supplements are one of the most common non-food causes of dark stool. They can turn it dark green or outright black, and this is a normal, expected side effect. If you recently started an iron supplement and noticed the change, that’s almost certainly the explanation.
Pepto-Bismol (bismuth subsalicylate) is the other big one. The bismuth compound reacts with trace amounts of sulfur in your digestive tract and produces a black compound that coats your stool. It can turn stool jet black, which looks dramatic but is completely harmless. Once you stop taking the medication, the color change resolves.
The important thing about medication-induced dark stool is what it doesn’t have: the stool won’t be sticky or tarry, and it won’t have an unusually foul smell. Those two features are what separate a harmless color change from something more serious.
Bleeding in the Upper Digestive Tract
When blood enters the digestive system from the esophagus, stomach, or upper small intestine, stomach acid breaks it down as it travels through. By the time it reaches your stool, the digested blood has turned jet black and gives the stool a distinctive tarry, sticky consistency. This is called melena, and it looks and feels noticeably different from stool that’s been darkened by food or medicine.
The conditions that cause this kind of bleeding include peptic ulcers (open sores in the stomach lining or upper intestine), inflammation of the stomach lining, and swollen veins in the esophagus. These are all situations where tissue in the upper GI tract is damaged enough to leak blood into the digestive pathway.
Melena also has a particularly strong, offensive odor that’s hard to miss. That smell is a byproduct of blood being broken down and digested. Stool that’s dark from iron supplements or Pepto-Bismol won’t have this distinctive smell.
How to Tell the Difference
Three features help you distinguish harmless dark stool from something that needs medical attention:
- Texture: Melena from bleeding is tarry and sticky, almost like roofing tar. Dark stool from food or medication has a normal consistency.
- Smell: Blood-related black stool has an unusually strong, foul odor that’s different from normal stool. Medication-darkened stool smells the same as it always does.
- Context: Think about what you’ve eaten or taken in the past 24 to 48 hours. If you recently started iron supplements, ate a pint of blueberries, or took Pepto-Bismol, the explanation is likely straightforward.
If the dark color goes away within a day or two of stopping the suspected food or medication, you have your answer.
Symptoms That Signal an Emergency
Dark, tarry stool paired with other symptoms can indicate significant blood loss. Dizziness, lightheadedness, vomiting blood (which may look like coffee grounds), or abdominal pain alongside black stool are signs of active bleeding that needs immediate evaluation. Even without those symptoms, stool that is persistently black, tarry, and foul-smelling warrants prompt medical attention.
What Happens at the Doctor’s Office
If there’s any uncertainty about whether your dark stool contains blood, a simple test called a fecal occult blood test can detect hidden blood that isn’t visible to the eye. It’s worth knowing that certain foods, supplements, and medications can cause false positives on this test. Rare red meat, vitamin C, iron supplements, and pain relievers like aspirin or ibuprofen can all skew results. Your doctor may ask you to avoid these for a few days before testing.
If the test confirms blood is present, the next step is typically an upper endoscopy, where a small camera examines the esophagus, stomach, and upper intestine to find the source of bleeding.
Dark Stool in Newborns
If you’re a new parent, very dark stool in the first couple of days is completely normal. Newborns pass a substance called meconium, which is typically dark brown or green and very sticky. It should appear within the first 24 to 48 hours after birth and then transition to lighter colors as feeding begins. After those first few days, however, black stool in an infant is not expected and should be evaluated by a pediatrician.