Most cases of melena (black stools) are from eating black foods or iron supplements.

The most common condition causing black stools is a bleeding ulcer.

Black stools caused by blood indicate a problem in the upper digestive tract.

Black tarry appearing stools medically referred to as melena usually indicates blood that has been in the GI tract for at least 8 hours.

Melena is four-times more likely to come from an upper gastrointestinal bleed than from the lower GI tract; however, it can also occur in either the duodenum and jejunum, and occasionally the portions of the small intestine and proximal colon.

Could be caused by food, supplements, medication, or minerals.

Iron supplements, alone or as part of a multivitamin for iron-deficiency anemia, may cause black stools or even green stools.

Dark blue, black or green foods may also cause black stools.

Substances that are often related to black stools include:

Black licorice


Iron supplements



Blood that comes from higher up in the digestive tract, such as the esophagus or stomach, may turn stool black, as the blood passes through the body and interacts with enzymes in the digestive process, the blood changes from red to black.

Blood from lower in the gastrointestinal system will be exposed to less of the digestive process and may keep its red color.

After melena is diagnosed, the test that will likely be most used in determining the cause of the bleeding will be an esophagogastroduodenoscopy (EGD).

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