Melena, Causes, Signs and Symptoms, Diagnosis and Treatment

Melena or melaena refers to the dark black, tarry feces that are associated with upper gastrointestinal bleeding.[1] The black color and characteristic strong odor are caused by hemoglobin in the blood being altered by digestive enzymes and intestinal bacteria.[2]

Iron supplements may cause a grayish-black stool that should be distinguished from melena,[3] as should black coloration caused by a number of medications, such as bismuth subsalicylate (the active ingredient in Pepto-Bismol), or by foods such as beetroot, black liquorice, or blueberries.[4]
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