Black stool is most often caused by something you ate, a supplement you’re taking, or a medication like Pepto-Bismol. But when black stool is also tarry, sticky, and has a strong foul smell, it can signal bleeding in the upper digestive tract, a condition called melena. The distinction between harmless and serious causes comes down to texture and context, and knowing the difference matters.
Harmless Causes: Food, Supplements, and Medications
Several everyday items can turn your stool dark or black without any bleeding involved. Iron supplements are one of the most common culprits. Black bowel movements are a normal and expected side effect of taking iron tablets. The color change happens because unabsorbed iron oxidizes as it moves through your digestive system.
Certain foods do the same thing. Black licorice, blueberries, blood sausage, and foods with dark artificial coloring can all darken stool noticeably. Activated charcoal, sometimes taken for digestive issues, will also turn stool jet black.
Pepto-Bismol and similar products containing bismuth are another frequent cause. The bismuth in the medication reacts with small amounts of sulfur naturally present in your saliva and digestive tract, forming a black compound called bismuth sulfide. This reaction can also temporarily blacken your tongue, which is harmless. The color change typically resolves within a few days of stopping the medication.
The key feature of these non-medical causes: the stool may be dark, but it generally has a normal texture and consistency. It won’t be sticky, tarry, or unusually foul-smelling.
When Black Stool Signals Bleeding
Melena, the medical term for black tarry stool caused by bleeding, looks and feels different from stool that’s simply dark. It has a sticky, tar-like consistency, and it carries a distinctly strong, unpleasant odor. This happens because blood from higher up in the digestive tract gets partially digested as it travels through. Gastric acid oxidizes the hemoglobin in blood, turning it dark, while digestive chemicals alter its texture along the way.
About 90% of melena originates above a specific anatomical landmark in the upper small intestine. That means the bleeding source is typically in the esophagus, stomach, or the first section of the small intestine. In rare cases, if your bowels move very slowly, bleeding from the lower small intestine or upper large intestine can produce melena too.
The most common conditions behind it include:
- Peptic ulcers: bleeding ulcers in the stomach or the first part of the small intestine (duodenum) are the leading cause
- Severe inflammation: conditions like gastritis (stomach lining inflammation) or esophagitis (esophageal inflammation)
- Ruptured blood vessels: enlarged veins in the esophagus or stomach can tear and bleed, often related to liver disease
- Tumors: growths in the upper digestive tract can bleed slowly or intermittently
Some of these conditions cause pain. Abdominal pain often points to a stomach ulcer or gastritis. Chest pain or pain when swallowing may suggest an esophageal problem. Pancreatic conditions tend to cause upper abdominal or back pain. But not all bleeding comes with pain. Silent ulcers, tumors, and ruptured blood vessels can produce melena with no other warning signs at all.
NSAIDs and Ulcer Risk
Regular use of nonsteroidal anti-inflammatory drugs like ibuprofen and naproxen is one of the most significant risk factors for developing the kind of bleeding that causes black tarry stool. Among people who take NSAIDs regularly, the point prevalence of stomach ulcers is roughly 15% to 30%. Clinically significant upper GI events occur in 3% to 4.5% of NSAID users, with serious complicated events (like significant bleeding) developing in about 1.5%.
If you take NSAIDs frequently and notice black, tarry stools, that combination is especially worth taking seriously. Alcohol use, being over 60, and taking blood thinners alongside NSAIDs all raise the risk further.
Symptoms That Require Immediate Attention
Black tarry stool on its own warrants a medical evaluation, but certain accompanying symptoms indicate severe or acute bleeding that needs emergency care. Fainting, feeling lightheaded, or dizziness suggest enough blood loss to affect circulation. A fast heart rate, pale skin, cold hands and feet, sweating, and confusion are signs of shock, which means blood loss has become life-threatening.
Acute GI bleeding can escalate quickly. Someone who initially feels fine may deteriorate as blood loss continues. Vomiting blood or material that looks like coffee grounds alongside black stool points to active upper GI bleeding.
How to Tell the Difference
The simplest way to sort harmless from concerning black stool is to think about what you’ve consumed in the past 48 to 72 hours. If you recently took iron, bismuth, activated charcoal, or ate a lot of blueberries or black licorice, that’s likely your answer, especially if the stool has normal consistency.
If you can’t identify an obvious dietary or medication cause, pay attention to texture. Stool that’s genuinely tarry (think the consistency of roofing tar), sticky enough to smear and be difficult to flush, and unusually foul-smelling is behaving like melena. Even if iron supplements are darkening your stool, a shift to a tarry texture or the appearance of red streaks is worth reporting. Iron turns stool black but shouldn’t make it tarry.
Black Stool in Babies
Newborns pass black, tar-like stool called meconium during the 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 other materials. It typically clears within the first three days as the baby starts feeding.
After those first few days, black stool in an infant is no longer expected. In a baby older than three days, thick black stool may indicate blood has entered the gastrointestinal tract and needs prompt evaluation by a pediatrician.