What should you know about dark green diarrhoea?

Green stool can occur when bile has not had time to change to its usual brown colour because contents are passing rapidly. Green vegetables, brightly coloured foods or supplements may also alter stool colour. Loose stools can accompany gastroenteritis or food poisoning, and exposure to unsafe food or water may be relevant. Ongoing diarrhoea with bloating or food-related symptoms can occur with food intolerance, while recurrent symptoms deserve a clinician’s review for conditions such as coeliac disease, Crohn's Disease, Irritable Bowel Syndrome or giardiasis. Colour alone cannot identify the cause.

Drink frequent small amounts of water or an oral rehydration drink, especially after each loose stool. Eat simple foods if hungry and avoid alcohol, very fatty meals and foods that clearly worsen symptoms. Note when the diarrhoea began, its colour, frequency, recent meals, travel, new medicines and any fever or vomiting. Wash hands carefully and avoid preparing food for others while diarrhoea continues. Do not take an anti-diarrhoeal medicine if you have blood in the stool or significant fever without checking with a healthcare professional.

Seek urgent medical help for severe or worsening abdominal pain, faintness, confusion, inability to keep fluids down, very little urine, blood or black stool, or signs of serious dehydration. Arrange prompt medical advice if diarrhoea is persistent, keeps returning, follows recent antibiotics or travel, or affects a young child, older adult or someone with a long-term illness. A clinician may assess hydration and decide whether stool or blood tests are appropriate.

Could a recent food, medicine, journey or infection explain the colour? What symptoms would make testing necessary? How should I replace fluids, and which foods or medicines should I avoid while recovering?