What causes black stools?

Bleeding from the stomach or upper small intestine can be digested as it moves through the gut, making stool black, sticky, and tar-like. Gastritis, a peptic ulcer, or Helicobacter pylori infection can irritate or damage the lining and may contribute to this pattern. Iron tablets and some medicines containing bismuth can also darken stool without bleeding. Foods with very dark colouring may do the same, but a new tarry appearance should not be dismissed based on colour alone.

Notice whether the stool is sticky or unusually foul-smelling, whether the change began after a medicine, and whether you have pain, vomiting, weakness, or dizziness. A symptom page on [Black Stools](/symptoms/black-stools/) gives more detail about how this appearance is described.

Arrange medical advice promptly if black stool is new, repeated, or tar-like. Make a list of medicines and supplements, including iron and pain relievers, and note when the colour changed. Do not stop a prescribed medicine without advice. A clinician may ask about abdominal symptoms, examine you, and arrange stool or blood testing or other tests based on the history.

Seek urgent care for black tarry stools with faintness, marked weakness, shortness of breath, fast heartbeat, severe abdominal pain, vomiting blood, or confusion. These features can accompany significant digestive bleeding and need immediate assessment. If you feel faint or unwell, do not drive yourself.

Ask whether the appearance could be related to bleeding, iron, bismuth, or a food; whether any medicine should be changed; and which warning signs should send you to urgent care. You can also ask whether testing for [Gastritis](/conditions/gastritis/), [Helicobacter Pylori Infection](/conditions/helicobacter-pylori-infection/), or [Peptic Ulcer](/conditions/peptic-ulcer/) is appropriate.