What should you know about food that cause black stool?

Dark foods can temporarily change stool colour, but black, tarry or sticky stool may indicate digestive-tract bleeding and needs careful attention. Foods such as black liquorice, blueberries and foods with very dark colouring may make bowel movements look darker. The colour usually becomes clearer after the food has passed. A food explanation is less reassuring when the stool looks shiny, tar-like or unusually sticky, has a strong unpleasant smell, or appears with weakness, dizziness or abdominal pain.

Colour alone cannot identify the cause. Iron tablets and bismuth-containing medicines can also turn stool black, although they are not foods. Bleeding from the oesophagus, stomach or the first part of the small intestine can produce melaena, which is typically black and tarry because blood has been altered during digestion. Possible causes include gastritis or a peptic ulcer; Helicobacter pylori infection can contribute to some stomach and ulcer problems. A clinician may ask about recent foods, medicines, alcohol use, pain, vomiting and changes in the stool’s texture.

If the stool became dark after a clearly identifiable food and you feel well, note what you ate and watch the next bowel movements. Do not stop a prescribed medicine without advice, but record iron, bismuth, anti-inflammatory painkillers and other medicines you take. Take a photo only if it can be done privately and safely; describing whether the stool is dark brown, black, sticky or tarry can help. Arrange medical advice if the colour persists, returns without an obvious explanation, or you have a history of ulcers, gastritis or digestive bleeding.

Seek urgent medical care for black tarry stool, especially if it is accompanied by fainting, marked dizziness, unusual weakness, shortness of breath, a fast heartbeat, vomiting blood or material that resembles coffee grounds, or severe abdominal pain. These features can occur with significant blood loss. Do not drive yourself if you feel faint. If you are unsure whether the stool is food-darkened or tarry, treat the uncertainty seriously and contact an urgent medical service for guidance.

You could ask: Could a medicine or supplement explain this colour? Does the texture suggest melaena rather than food staining? Do I need tests for bleeding, gastritis, an ulcer or Helicobacter pylori infection? Which symptoms should prompt emergency care? Bring the timing of the colour change, recent foods, medicine names and any pain, vomiting, dizziness or bowel changes.