Dark stool indicates that blood is passing the upper gastrointestinal (GI) tract--esophagus, stomach and the upper intestine. Dark stool appears sticky and black because blood mixes with digestive juices. Dark stool also occurs from eating certain items.

Mallory-Weiss Tear

A Mallory-Weiss tear causes dark stool because mucous membrane in the esophagus tears and bleeds. MedlinePlus Medical Encyclopedia says long-term vomiting, coughing and epileptic convulsions cause such tears.

Peptic Ulcer

Peptic ulcers develop in the stomach and upper part of the small intestine. The erosion in stomach and intestinal linings lead to dark, sticky stool.

Blood Vessels

Blood vessel problems in the GI tract lead to dark-colored stool. These problems include wide, overgrown blood vessels in the esophagus and stomach and intestinal ischemia--restricted blood flow to intestines.

Ingested Items

Items consumed cause black stool. MedlinePlus says these items include black licorice, iron pills, medications containing bismuth like Pepto-Bismol, lead and blueberries.

Medical Intervention

If you notice a change in the color of your stool, go to the doctor for an examination to make sure you don't have a serious health condition.

Treatment

Treatments include increase in fiber, smoking cessation, prescription antibiotics and overnight observation at a hospital, depending on the cause of the dark stool.

Source:

MedlinePlus Medical Encyclopedia: Mallory-Weiss tear

Medline Plus: Peptic Ulcer

MedlinePlus: Intestinal ischemia and infarction

More Information:

MedlinePlus Medical Encyclopedia: Bloody or tarry stools