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What are the Causes of Black Tarry Stools?

author image J. Lucy Boyd
J. Lucy Boyd, RN, BSN has written several nonfiction books including "The Complete Guide to Healthy Cooking and Nutrition for College Students." She is frequently called upon to provide career guidance to medical professionals and advice to parents of children with challenges. She also loves teaching others to cook for their families.
What are the Causes of Black Tarry Stools?
Black, tarry stools may be alarming and require a number of medical tests. Photo Credit: Ridofranz/iStock/Getty Images

Black, tarry stools are the result of bleeding in the gastrointestinal tract. Specifically, they may originate from the stomach, the esophagus or the upper portion of the small intestine. The bowel movement appears to look like black, soft tar as a result of the blood becoming partially digested as it moves through the gastrointestinal tract. Severe bleeding may be a medical emergency and black, tarry stools always warrant a medical evaluation by a family physician, internal medicine specialist or gastroenterologist. There are several potential causes for black, tarry bowel movements, which are medically referred to as melena.

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A gastrointestinal ulcer is a sore in the digestive tract. It affects the lining of one of the organs, sometimes causing bleeding. An ulcer in the esophagus, stomach or upper intestine can cause black, tarry stools. These ulcers are frequently caused by the Heliobacter pylori bacterium, which weakens the lining of the affected organ. Medications can also cause ulcers in the stomach or duodenum. Common offenders include non-steroidal anti-inflammatory drugs, such as ibuprofen or aspirin, explains the American Academy of Family Physicians.


A blow to the throat or abdominal area may cause bleeding that results in black, tarry stools. This may occur due to an automobile accident, physical assault, gunshot wound, stabbing or other injury. A swallowed object that is large or has a sharp edge may also cause internal trauma and bleeding. The lining of the esophagus may tear due to violent vomiting or retching. Corrosive or poisonous substances may also damage the esophagus, leading to bleeding.

Dilated Veins

The veins of the esophagus or stomach may become engorged with blood. Engorged veins are referred to as varices. They are usually the result of a problem with the liver, often cirrhosis, that causes elevated pressure within several veins in the abdominal region. As the varices become dilated, they may rupture, relates the Merck Manuals Online Medical Library. Bleeding ensues, leading to black, tarry stools; this bleeding is often massive.

Impaired Blood Flow

Impaired blood flow to the small intestine can cause a portion of the wall of the small intestine to die, leading to black, tarry bowel movements. The impaired blood flow may be the result of a small blood clot, a tumor or an abnormality in the blood vessel.

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