What should you know about very dark loose stool?

Loose stool may look darker after foods with deep colouring or products containing iron or bismuth. A stool that is truly black, sticky, shiny, or tar-like is different from ordinary brown diarrhoea and can indicate digested blood from the stomach or upper intestine. The colour alone cannot identify the cause.

Diarrhoea can also occur with gastroenteritis or food poisoning, while ongoing digestive symptoms may be assessed alongside coeliac disease, food intolerance, Crohn's disease, giardiasis, irritable bowel syndrome, or an overactive thyroid. These conditions do not all cause black stool, so an examination and medication review may be needed.

Notice whether the stool is dark brown or black and tar-like, and whether the change began after a new medicine, supplement, or strongly coloured food. Keep drinking small, frequent amounts of fluid while loose stools continue. Avoid anti-diarrhoeal medicine until a clinician has considered bleeding, particularly if the stool is black or you feel unwell.

Arrange medical advice if the unusual colour persists, returns, or occurs with repeated diarrhoea. Take a list of medicines and supplements, and describe any recent travel, sick contacts, fever, abdominal pain, or change in bowel pattern.

Seek urgent medical care for black tar-like stool, visible blood, vomiting blood or material resembling coffee grounds, fainting, marked dizziness, confusion, severe weakness, severe abdominal pain, or trouble keeping fluids down. These symptoms can signal bleeding or significant fluid loss.

Get prompt advice if diarrhoea is frequent, you have signs of dehydration such as very little urine, or you have a condition or medicine that raises bleeding risk. Children, older adults, and people who are pregnant or medically vulnerable may need earlier assessment.

Ask: Could a medicine, supplement, food, infection, or bleeding explain this colour? Do I need stool or blood tests? What symptoms should send me to urgent care, and which fluids or medicines are suitable while I recover?