Black tarry stool, known medically as melena, is stool that appears dark black, sticky, and tar-like. It typically signals bleeding somewhere in the upper digestive tract, such as the esophagus, stomach, or the first part of the small intestine. The stool turns black because blood is partially digested by stomach acid as it travels through the gut, changing its color from red to dark black. Not every case of black stool means bleeding, though. Several common foods and medications can also darken stool without any cause for concern.
Why Bleeding Turns Stool Black
When blood enters the upper digestive tract, it doesn’t stay red for long. Stomach acid breaks down the hemoglobin in red blood cells, converting it into a dark compound called hematin. As this altered blood moves through the intestines and mixes with stool, it produces the characteristic black, sticky, tar-like appearance and a distinctly foul smell. The further the bleeding is from the rectum, the darker and more digested the blood appears by the time it exits the body. Bright red blood in stool, by contrast, usually points to bleeding lower in the digestive tract, such as the colon or rectum.
Common Medical Causes
Peptic ulcers are the most frequent cause of upper gastrointestinal bleeding. These are open sores on the lining of the stomach or the upper small intestine, most often caused by a bacterial infection (H. pylori) or regular use of anti-inflammatory painkillers like ibuprofen, aspirin, and naproxen. Blood thinners also raise the risk.
Gastritis, or inflammation of the stomach lining, can produce shallow breaks that bleed. The same culprits apply here: H. pylori infection, painkillers, blood thinners, and heavy alcohol use. Esophagitis, inflammation of the esophagus usually driven by chronic acid reflux, can also lead to ulcers that bleed enough to cause melena.
More serious causes include esophageal or stomach varices, which are swollen veins that can burst and bleed heavily. Varices are most commonly linked to liver cirrhosis. Mallory-Weiss tears, small rips in the lower esophagus caused by severe or prolonged vomiting, are another source. Benign tumors or cancers of the esophagus or stomach can weaken the digestive lining and expose blood vessels underneath.
Upper GI bleeding is not rare. In the United States alone, it accounts for more than 250,000 hospital admissions each year, with annual incidence estimates ranging from 39 to 172 cases per 100,000 adults depending on the population studied.
Foods and Medications That Mimic Melena
Before assuming the worst, it’s worth considering what you’ve eaten or taken recently. Several substances turn stool black without any bleeding involved:
- Iron supplements, one of the most common causes of harmless black stool
- Bismuth subsalicylate (the active ingredient in Pepto-Bismol)
- Activated charcoal
- Dark foods like black licorice, blueberries, and blood sausage
The key difference is texture and smell. Stool darkened by food or medication is typically firm and looks normal apart from its color. True melena is sticky, tar-like, and has a strong, unusually foul odor that’s hard to miss. If you stop taking the suspected supplement or food and the color returns to normal within a day or two, bleeding is unlikely.
Black Stool in Newborns vs. Older Children
Newborns pass a substance called meconium during their first few days of life. It’s thick, dark greenish-black, and extremely sticky. This is completely normal. Meconium is made up of everything the baby swallowed in the womb: amniotic fluid, mucus, bile, and skin cells. Most babies pass it within 48 hours of birth.
After those first few days, black tarry stool should not appear again. In a baby older than three days, tar-like black stool may be a sign that blood has entered the gastrointestinal tract, and it warrants a call to the pediatrician right away.
How the Source of Bleeding Is Found
When black tarry stool suggests genuine bleeding, doctors typically start with a stool test to confirm the presence of hidden blood. If the test is positive, the next step is usually an upper endoscopy, a procedure where a thin, flexible camera is passed through the mouth to visually inspect the esophagus, stomach, and upper small intestine. This is the primary tool for finding the bleeding source, and guidelines recommend performing it within 24 hours for most patients with suspected upper GI bleeding.
Blood tests are also drawn to check hemoglobin levels, which indicate how much blood has been lost. In some cases, imaging of the abdomen may be done first to look for abnormalities before proceeding to endoscopy.
What Treatment Looks Like
Treatment depends on where the bleeding is coming from and how severe it is. During an upper endoscopy, doctors can often stop the bleeding on the spot using small metal clips, heat cauterization, or band ligation to seal off the bleeding vessel. For conditions like Mallory-Weiss tears or Dieulafoy lesions (exposed arteries in the stomach wall), clips and band ligation are considered the go-to approaches because they cause less damage to surrounding tissue.
Acid-reducing medications given through an IV are a standard part of treatment. These drugs reduce stomach acid production, giving ulcers and damaged tissue a chance to heal and lowering the risk of re-bleeding. Patients typically receive these medications for several days during a hospital stay.
Blood transfusions are used when significant blood has been lost. If endoscopy can’t stop the bleeding or it recurs, a procedure called embolization may be performed, where a specialist blocks the bleeding vessel through a catheter threaded into the artery supplying it.
About 15% of nonvariceal upper GI bleeds progress to severe hemorrhage requiring endoscopic or surgical treatment. Most cases, however, are self-limited or manageable with endoscopy. In-hospital mortality for patients admitted with upper GI bleeding sits around 5 to 6%, though variceal bleeding from conditions like liver cirrhosis carries a much higher mortality rate, approaching 20%.
Signs That Warrant Urgent Attention
Black tarry stool accompanied by lightheadedness, dizziness, rapid heartbeat, weakness, or vomiting blood (which may look like coffee grounds) suggests active and potentially significant bleeding. Fainting or feeling like you might pass out points to substantial blood loss. Even without those symptoms, true melena that persists for more than a day or two is not something to wait on, particularly if you take blood thinners, anti-inflammatory painkillers, or have a history of liver disease or ulcers.