Medicines that can cause black stool

Iron commonly makes stool dark green or black. Bismuth-containing products can also turn the tongue or stool dark. Bleeding is more concerning when stool is shiny, sticky, unusually foul-smelling, or accompanied by weakness, dizziness, abdominal pain, or vomiting blood. Gastritis, Helicobacter Pylori Infection, and Peptic Ulcer can cause bleeding in the upper digestive system.

Do not assume a new black stool is harmless because you take a medicine. The product name, amount, timing, and stool texture help a clinician judge the situation.

Check the labels of iron, bismuth, and other recently started products, and keep a list of prescribed and non-prescribed medicines. Contact a clinician or pharmacist for advice before changing a prescribed medicine. Avoid taking additional anti-inflammatory painkillers until a professional has reviewed black stool, as they can irritate the stomach in some people.

Seek emergency help for tar-like stool with fainting, severe weakness, rapid breathing, confusion, severe abdominal pain, or vomiting blood or material resembling coffee grounds. Arrange prompt assessment for repeated black stools, even if discomfort is mild. A clinician may need to check for blood loss and digestive causes.

Bring the medicine packaging or a medication list. Mention when the colour changed, whether the stool is sticky, any pain or dizziness, and use of anti-inflammatory painkillers or blood-thinning treatment.