What causes dark stool?

Dark stool may be caused by foods or medications by bleeding within the digestive tract.

Food and medication causes of dark stool

Dark stool may be caused by foods or medications including:

  • Beets
  • Black licorice
  • Blueberries
  • Iron supplements
  • Medications containing bismuth subsalicylate (for example, Kaopectate or Pepto-Bismol)

Digestive tract causes of dark stool

Dark stool can also be caused by conditions of the digestive tract including:

  • Anal fissure (tear or crack in anal tissue)
  • Atrophic gastritis (inflammation and thinning of the stomach lining)
  • Bacterial, parasitic or viral infection of the gastrointestinal tract
  • Cancer of the digestive tract
  • Colitis
  • Diverticular disease
  • Gastroesophageal reflux disease (GERD)
  • Inflammatory bowel disease
  • Ulcers of the stomach or duodenum

Serious or life-threatening causes of dark stool

In some cases, dark stool may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These include:

  • Bleeding disorders
  • Bleeding esophageal varices (life-threatening rupture and hemorrhage of swollen veins in the esophagus
  • Colorectal cancer
  • Intussusception (telescoping of the intestines into themselves)
  • Mallory-Weiss tear (a tear in the lining of the esophagus from severe vomiting or coughing)
  • Perforated peptic ulcer (bleeding stomach or intestinal ulcer)

Questions for diagnosing the cause of dark stool

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your dark stool including:

  • When did you first notice your dark stools?
  • How would you describe their color and consistency?
  • Had you eaten any dark-colored foods prior to developing dark stool?
  • Have you had any trauma to your abdomen or swallowed any objects?
  • Do you have any other symptoms?
  • What medications and supplements are you taking?

What are the potential complications of dark stool?

Because dark stool can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

  • Anemia (low red blood cell count)
  • Deterioration of bowel function
  • Spread of cancer
  • Spread of infection
  • Surgery to remove parts of the digestive tract due to serious infection or malignant condition


  1. Bloody or tarry stools. MedlinePlus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003130.htm.
  2. Bleeding in the digestive tract. National Digestive Diseases Information Clearinghouse (NDDIC). http://digestive.niddk.nih.gov/ddiseases/pubs/bleeding/index.htm.
  3. Collins RD. Differential Diagnosis in Primary Care, 5th ed. Philadelphia: Lippincott, Williams & Williams, 2012.

What is dark stool?

Darkening of the stool may be a normal occurrence related to specific foods or medications; however, it can sometimes be a sign of a more serious condition such as bleeding in the intestinal tract. When related to foods, blueberries, beets, or black licorice are often the cause. Stool passed after eating these foods may be dark brown, bluish, reddish, or black. Iron supplements and medications ... Read more about dark stoolintroduction


What other symptoms might occur with dark stool?

The symptoms of dark stool are generally related to food or medications that pass through the digestive tract or something more serious such as digestive tract bleeding.

Digestive symptoms that may occur along with dark stool

Dark stool may accompany other symptoms affecting the digestive tract including:

Medical Reviewer: William C. Lloyd III, MD, FACS Last Annual Review Date: Aug 9, 2013 Copyright: © Copyright 2014 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.

This Article is Filed Under: Digestive System

Did You Know?

View Source

Irritable bowel syndrome (IBS) is one of the most common disorders diagnosed by doctors. In fact, it's estimated that as many as 20 percent of adults have symptoms of IBS.