Black stool without visible blood: what to know

Iron tablets, bismuth-containing stomach remedies, and strongly pigmented foods can darken stool. A stool that is jet black, sticky, or unusually difficult to flush is different from ordinary dark brown stool. Blood from the upper digestive tract can turn black as it moves through the bowel, so not seeing red blood does not rule it out.

Possible digestive causes include irritation of the stomach lining, a peptic ulcer, or Helicobacter pylori infection. The colour alone cannot identify which explanation applies.

Recall what you ate and any new tablets or remedies, and note when the change began. Do not stop a prescribed medicine without advice. Arrange a prompt clinical review if the stool remains black, becomes tarry, or returns, especially if you take medicines that can irritate the stomach or affect clotting. A clinician may review your medicines and decide whether stool or blood testing is needed.

Seek emergency help for black tarry stool with dizziness, fainting, unusual weakness, confusion, vomiting blood, severe abdominal pain, breathlessness, or a fast heartbeat. These signs can accompany significant blood loss and should not be judged by whether red blood is visible.

Could my food, iron, or stomach remedy explain the colour? Does the texture suggest digested blood? Which medicines should I avoid until this is checked, and what tests would clarify the cause?