Dark black tarry-colored stool usually indicates you are bleeding internally in your upper gastrointestinal (GI) tract. The digestive juices in this part of your GI tract turn the blood to a black color. In fact, if you vomit it up, it looks like coffee grounds. This may be an indication of an ulcer or inflammation in your esophagus, stomach, or first part of your small intestine. This condition can be associated with abdominal pain. Taking aspirin or non-steroidal anti-inflammatory drugs such as ibuprofen can cause it. Other causes of black stools are a tear in esophagus from violent vomiting called Mallory-Weiss tear, and chronic alcoholism can lead to dilated veins in the esophagus and stomach that can cause bleeding called varices.
Maroon or bright red blood in your stool usually comes from a lower GI bleed, the lower small intestines, large colon, rectum, and anus. One of the more common causes of a lower GI bleed is hemorrhoids which are dilated veins in the rectum and anus; also cuts or fissure of the anus can cause blood in the stool. Diverticulosis is a condition where small abnormal pouches can develop in the colon and sometimes bleed, as well as abnormal blood vessels can grow in the lower GI tract called arterio-venous malformations (AVM) and they can cause lower GI bleeds. Colon cancer can also cause a lower GI bleed as well as Inflammatory Bowel disease such as Crohn’s or Ulcerative colitis. In medical school they teach another common cause of a lower GI bleed is a massive briskly bleeding upper GI bleed! And always check for a foreign body that may have been inserted and cause trauma to the rectum and anus.