Probiotics are beneficial microorganisms that contribute to the diverse community of bacteria and other microbes in the gut, collectively known as the gut microbiota. These supplements are often taken to support digestive health, helping to maintain balance within the intestinal tract. Introducing new supplements or making changes to one’s diet can sometimes lead to alterations in normal bodily functions, including digestive patterns and stool characteristics.
Probiotics and Stool Color
Probiotics typically do not directly cause dark or black stool. While these beneficial bacteria influence gut microbiota and various digestive processes, they are generally not associated with a darkening of stool color. Stool color is primarily influenced by bile, a greenish-yellow fluid produced by the liver, and by the food and medications consumed.
Some research suggests certain probiotic strains might lead to a slight stool darkening over several weeks, but not to the extent of black or tarry stool. If black or unusually dark stool appears after starting probiotics, it is more likely due to other, unrelated factors.
Understanding Dark Stool Causes
Dark or black stool can stem from various sources. Dietary factors are a common cause, as consuming dark-colored foods like black licorice, blueberries, beets, dark chocolate, and blood sausage can temporarily alter stool appearance.
Certain medications and supplements can also result in dark stools. Iron supplements, for example, are a well-known cause of black or very dark green stool. Bismuth subsalicylate, found in some over-the-counter stomach upset medications, can also turn stool black. Activated charcoal, used for poisoning or as a supplement, also produces black stool.
A more concerning cause of dark stool is melena, which refers to black, tarry, and often foul-smelling stool resulting from bleeding in the upper gastrointestinal (GI) tract. This darkening occurs because blood has been digested as it travels through the esophagus, stomach, or small intestine. Common medical conditions leading to upper GI bleeding include peptic ulcers, gastritis, esophageal varices, and Mallory-Weiss tears. Less commonly, certain cancers in the upper GI tract can also cause this type of bleeding.
Recognizing Concerning Stool Changes
Distinguishing between harmless dark stool and a serious condition like melena is important. Melena is jet black, sticky or tarry in consistency, and has an unusually strong, offensive odor. This distinctive smell is a byproduct of blood being broken down and digested in the GI tract. Stool dark due to diet or supplements usually lacks this tarry consistency and strong odor.
Accompanying symptoms are important indicators of a serious issue. If dark, tarry stool is present alongside symptoms such as abdominal pain, nausea, vomiting (especially if vomit contains blood or looks like coffee grounds), unexplained weight loss, or changes in bowel habits, medical attention is warranted. Other concerning signs include dizziness, lightheadedness, fatigue, weakness, a rapid heartbeat, or shortness of breath. These symptoms can signal significant blood loss. If you notice persistent black stool, particularly if it has a tarry consistency or foul smell, or if it is accompanied by any of these concerning symptoms, seek medical consultation immediately.