Black or Tarry Stools

Black or tarry stools are usually a result of bleeding into the upper GI tract. This is a serious sign and needs immediate investigation to rule out pathology (ulcer, Crohn's disease, colitis, cancer etc). Also need to ask whether there has been an ingestion of iron, charcoal, or bismuth products. Bismuth is found in over the counter medication, such as Pepto-Bismol and other nutritional supplements. When bismuth oxidizes in the GI tract it turns black, and could therefore stain the stool. A heavy meat diet can also cause black stools.

Reference: Weatherby, D. (2004). Signs and Symptoms Analysis from a Functional Perspective. Jacksonville, OR: Bear Mountain Publishing.