What should you know about black diarrhea?

Iron, bismuth-containing medicines, and dark foods can turn loose stool dark. Diarrhoea from infection or bowel irritation may be watery and urgent, while black, sticky, tar-like stool can indicate digested blood higher in the digestive tract. Conditions including Food Poisoning, Gastroenteritis, Crohn's Disease, Coeliac Disease, or Food Intolerance can cause diarrhoea, but they do not make every black stool harmless. Hyperthyroidism, Giardiasis, and Irritable Bowel Syndrome can also affect bowel habits in different ways.

Drink frequent small amounts of fluid and record the number and appearance of bowel movements. Oral rehydration can help replace water and salts when diarrhoea is frequent. Eat lightly if you feel able, and avoid alcohol until you recover. Check whether a new supplement or medicine explains the colour, but do not discontinue prescribed treatment without advice. Contact a clinician promptly if black diarrhoea continues, has no clear explanation, or comes with abdominal pain, fever, or weakness.

Go to urgent care for black tarry diarrhoea with fainting, confusion, severe weakness, fast breathing, severe abdominal pain, repeated vomiting, or vomiting blood. Seek prompt medical advice for signs of dehydration such as very little urine, a dry mouth, intense thirst, or dizziness when standing. Children, older adults, pregnant people, and anyone with serious long-term illness may need earlier assessment.

Could my medicine or food explain the colour? Do I need stool or blood tests? How should I replace fluids? Which changes mean I should attend urgent care?