Sometimes black stool: what it can mean and what to do

Sometimes black stool can come from iron, bismuth, or dark foods, but black, sticky, tarry stool may indicate bleeding in the upper digestive tract and needs prompt medical attention. Colour alone cannot establish the cause. Notice whether the stool is genuinely black rather than dark brown, and whether it has a tar-like texture or unusually strong odour.

Iron tablets and medicines containing bismuth can turn stool dark or black without causing bleeding. Dark foods may also temporarily change its appearance. A clinician may be more concerned when the stool looks shiny, sticky, or tarry, because blood can be altered as it passes through the stomach or small intestine. Possible sources include irritation of the stomach lining, a peptic ulcer, or bleeding associated with Helicobacter pylori infection.

Other clues include upper abdominal discomfort, nausea, indigestion, unusual tiredness, or becoming light-headed. These symptoms do not identify the cause by themselves. A medication review, examination, and sometimes stool or blood testing can help separate a colour change from digestive-tract bleeding.

Make a note of when the colour changed, how many times it happened, and whether the stool was loose, sticky, or tarry. List recent foods, iron or bismuth products, pain medicines, and any medicines that affect clotting. Do not stop a prescribed medicine without advice, but contact a clinician promptly if the black stool is unexplained, recurs, or has a tarry appearance.

If you feel well and can clearly connect the colour to a food or product, arrange medical advice if it does not settle after that exposure has ended. A healthcare professional can decide whether you need examination or testing.

Seek urgent medical care for black, tarry, or sticky stool, especially if you also have dizziness, fainting, marked weakness, shortness of breath, a rapid heartbeat, pale or clammy skin, worsening abdominal pain, or vomiting blood or material that looks like coffee grounds. These can be signs of significant digestive-tract bleeding. Do not drive yourself if you feel faint or confused.

Even without those warning signs, arrange prompt assessment for repeated unexplained black stools or black stool after starting a medicine that can increase bleeding risk. Bring or photograph the product packaging and tell the clinician about alcohol use, previous ulcers, liver problems, and recent vomiting.

You could ask: Could my medicines or supplements explain the colour? Does the texture suggest digested blood? Do I need blood or stool tests? Could stomach inflammation, a peptic ulcer, or Helicobacter pylori be involved? Which symptoms should send me to urgent care?