Consuming blueberries, beets or black licorice can cause black stools, according to About.com and HealthGrades. Several common medicines and supplements, such as iron supplements, aspirin and NSAIDs, can also cause black stools, as can medicines that contain bismuth, such as Pepto-Bismol, notes WebMD.
While foods can cause black stools, it's important to note that food consumption is not the only potential cause. Experiencing black stools, particularly for a prolonged period of time, can be a sign of distress in the gastrointestinal system. In instances of gastrointestinal distress, black stools result from bleeding in the esophagus, stomach or small intestines, explains WebMD. Conditions such as colon polyps, gastritis and Crohn's disease can all result in the expulsion of very dark brown or black stools.
When black stools result from a gastrointestinal issue, there is often a difference in the consistency of the waste. Black stools that result from a gastrointestinal issue are often softer and may have a tar-like consistency, according to HealthGrades. Individuals who experience unexplained black stools should seek immediate medical care. This is particularly vital if visible blood accompanies the black stool or if the individual experiences excessive sweating, a rapid heartbeat, chest pain, abdominal pain or loss of consciousness.