Black stool causes in adults: what they can mean

Iron tablets and bismuth-containing stomach remedies can darken stool. Some foods can also make bowel movements look very dark. Bleeding from the oesophagus, stomach, or first part of the small intestine may instead produce stool that is black, sticky, and tar-like, sometimes called melaena. The blood has been altered as it travels through the digestive system, so it may not look red.

Upper digestive bleeding can occur with gastritis, a peptic ulcer, or infection with Helicobacter pylori. These conditions may also cause upper abdominal discomfort, nausea, indigestion, weakness, or light-headedness, although symptoms vary.

Think about when the colour began and whether you recently started iron, bismuth, or a new medicine. Note the stool texture, number of bowel movements, abdominal symptoms, vomiting, and any dizziness. Do not stop a prescribed medicine without medical advice. Contact a clinician promptly if the stool is tarry or the cause is unclear; an examination and stool or blood testing may be needed.

Seek emergency help for black tarry stool with fainting, marked weakness, confusion, breathlessness, a racing heartbeat, severe abdominal pain, vomiting blood, or repeated bleeding. These features can accompany significant digestive-tract blood loss. Even without them, arrange prompt medical review for new black stool that cannot be explained by a food or medicine.

Ask whether your medicines or supplements can explain the colour, whether testing for digestive bleeding is appropriate, and whether symptoms suggest gastritis, a peptic ulcer, or Helicobacter pylori infection.