If you have black poop, what does that mean?

Bleeding from the stomach or the first part of the small intestine may be digested as it moves through the bowel, producing a black, shiny or tar-like stool with a strong smell. Conditions such as a peptic ulcer, gastritis or Helicobacter pylori infection can be involved, but colour alone cannot identify the cause.

Iron tablets and medicines containing bismuth may darken stool without bleeding. Tell a clinician what you have taken and whether the change happened once or repeatedly.

If the stool is genuinely black and you have not taken iron or bismuth, arrange prompt medical advice. Keep a note of when it began, how often it has happened, and any abdominal pain, vomiting, dizziness or change in medicines. Do not stop prescribed medicines without advice.

Seek emergency care for black stool with fainting, marked weakness, confusion, fast breathing, severe abdominal pain, vomiting blood or vomit that looks like coffee grounds. These features can signal significant digestive-tract bleeding and need immediate assessment.

Ask whether the appearance could be melaena, whether you need blood tests or a stool assessment, and whether your medicines may irritate the stomach. Mention alcohol use, pain-relief medicines, iron, bismuth and any previous ulcer symptoms.