Dark stool usually comes from something you ate, drank, or took as a supplement. Foods like blueberries, black licorice, and blood sausage can turn your poop noticeably darker, and so can iron pills and bismuth-based medications like Pepto-Bismol. In most cases, the color returns to normal brown within a few days once you stop consuming whatever caused the change. The important exception is when dark stool signals bleeding somewhere in your digestive tract, which produces a distinct jet-black, tarry appearance that looks and smells very different from a food-related color shift.
Foods and Drinks That Darken Stool
Several everyday foods can make your stool appear dark brown or even black. Blueberries are one of the most common culprits, along with black licorice, blood sausage, and foods with dark artificial coloring. Beets can produce a deep reddish-brown that some people mistake for blood. Dark chocolate, blackberries, and heavily dyed foods like certain cereals or frosting can also have a noticeable effect.
The color change happens because pigments in these foods aren’t fully broken down during digestion. It’s harmless, and your stool should return to its typical brown color within a few days after you stop eating the food in question. If you notice dark stool and recently ate any of these foods, that’s almost certainly the explanation.
Medications and Supplements
Iron supplements are one of the most reliable causes of black stool. Your body only absorbs a portion of the iron you take, and the unabsorbed iron oxidizes as it moves through your intestines, turning your stool dark green or black. This is completely expected and not a reason to stop taking iron unless your doctor advises otherwise.
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and Kaopectate, also turns stool black. Bismuth reacts with small amounts of sulfur in your saliva and digestive tract, forming a dark compound. The effect is temporary and clears up once you stop taking the medication. Activated charcoal, sometimes used for gas or bloating, produces a similar jet-black color.
When Dark Stool Signals Bleeding
The type of dark stool that warrants concern looks and feels distinctly different from what food or supplements produce. It’s called melena: jet black, tarry, and sticky, almost like roofing tar. It also has a particularly strong, foul odor that’s noticeably worse than normal stool. That smell comes from blood being broken down by stomach acid and bacteria as it travels through your digestive tract. The longer the blood has been in your system, the darker and more pungent the stool becomes.
Melena typically means bleeding is happening somewhere in the upper digestive tract: the esophagus, stomach, or the first part of the small intestine. Peptic ulcers are among the most common causes. These are open sores in the stomach lining or upper intestine, often triggered by a bacterial infection or long-term use of pain relievers like ibuprofen, naproxen, and aspirin. NSAIDs are well established as a cause of upper gastrointestinal bleeding, and they can also cause damage and blood loss in the lower intestine. Even small bowel lesions are commonly seen in people who use these medications regularly.
Other causes of upper GI bleeding include gastritis (inflammation of the stomach lining), tears in the esophagus, and swollen veins in the esophagus or stomach, which are more common in people with liver disease.
How to Tell the Difference
The key distinction is texture and smell. Dark stool from food or supplements is typically firm or normal in consistency. It might look alarming in the toilet bowl, but it doesn’t have that sticky, tar-like quality. Melena, by contrast, is unmistakably different: it clings, it smears, and the odor is hard to ignore.
A practical first step is to think back over the past day or two. Did you take iron, Pepto-Bismol, or activated charcoal? Did you eat blueberries, black licorice, or heavily dyed food? If so, stop consuming it and watch whether your stool returns to brown within a few days. If it doesn’t, or if you can’t identify an obvious dietary cause, that’s worth investigating.
If you’re experiencing other symptoms alongside dark stool, such as dizziness, fatigue, abdominal pain, or vomiting that looks like coffee grounds, those are signs of active bleeding that needs prompt medical attention.
How Doctors Test for Hidden Blood
When the cause of dark stool isn’t obvious, doctors can check for hidden blood using a simple stool test. The most common version is called a fecal immunochemical test (FIT), which detects human blood proteins in a stool sample. With a single application, FIT picks up about 80% of colorectal cancers and 20% to 30% of advanced precancerous growths. It’s more accurate than the older guaiac-based test, which could be thrown off by certain foods and medications.
A positive result doesn’t automatically mean cancer or a serious condition. It means blood is present and further investigation is needed, usually with a colonoscopy or upper endoscopy depending on where the bleeding is suspected.
Dark Stool in Newborns
If you’re a new parent, dark stool in your baby’s first couple of days is completely normal. A newborn’s first bowel movements are called meconium: a thick, sticky, blackish-green substance that doesn’t smell like regular stool. Babies typically pass meconium within 24 to 48 hours after birth. Once they start drinking breastmilk or formula, their digestive system pushes out the remaining meconium and stool gradually transitions to the yellowy, seedy texture of normal newborn poop. Healthcare providers usually confirm this transition is happening before sending you home from the hospital.