Black runny stool: what to know

Runny stool is often caused by faster movement through the bowel, such as during an infection or after a dietary change. Black colour can follow iron or bismuth medicines and some deeply coloured foods. If the stool is shiny, sticky, tar-like, or unusually foul-smelling, digested blood is a concern. Gastritis, a peptic ulcer, or Helicobacter pylori infection can affect the upper digestive tract and may be associated with this appearance. The symptom does not identify one cause by itself.

Arrange same-day medical advice if the black runny stool is unexplained or continues. Keep a note of its appearance, any abdominal pain, vomiting, dizziness, and medicines or supplements taken. Drink small, frequent amounts of water or an oral rehydration solution if you can keep fluids down. Do not stop prescribed treatment without advice, and avoid aspirin or ibuprofen until a clinician has considered bleeding.

Go to emergency care for fainting, severe dizziness, confusion, cold clammy skin, intense abdominal pain, vomiting blood or coffee-ground material, worsening weakness, or very little urine. These signs can accompany blood loss or dehydration. If you feel well but notice one new black stool after taking iron or bismuth, contact a healthcare professional for confirmation rather than relying on colour alone.

Could my medicine or supplement explain the colour? Does the texture suggest digested blood? Do I need blood testing or a stool assessment? How should I replace fluids while the cause is being checked?