What should you know about dark diarrhea stool?

The shade, texture, smell, duration, and accompanying symptoms all matter. Iron, bismuth-containing products, and dark foods can change stool colour, but black sticky stool that resembles tar can indicate bleeding higher in the digestive tract.

Loose dark stool can occur with an intestinal infection such as [Food Poisoning](/conditions/food-poisoning/), [Gastroenteritis](/conditions/gastroenteritis/), or [Giardiasis](/conditions/giardiasis/). Cramping, nausea, vomiting, fever, bloating, or an unpleasant smell may accompany infection. Food colour and some products can produce a dark appearance without bleeding.

Ongoing diarrhoea may also occur with [Food Intolerance](/conditions/food-intolerance/), [Coeliac Disease](/conditions/coeliac-disease/), [Irritable Bowel Syndrome](/conditions/irritable-bowel-syndrome/), or inflammatory bowel disease such as [Crohn's Disease](/conditions/crohns-disease/). A fast heartbeat, tremor, heat intolerance, and weight change can accompany [Hyperthyroidism](/conditions/hyperthyroidism/), which can alter bowel habits. These patterns overlap, so stool colour does not establish a diagnosis.

Drink frequent small sips of water or an oral rehydration solution, particularly after repeated loose stools or vomiting. Eat simple foods if you feel able, and avoid alcohol and foods that clearly worsen symptoms. Keep a note of the stool colour, frequency, recent meals, medicines, travel, and whether anyone else is unwell.

Contact a clinician if dark diarrhoea continues, keeps returning, or comes with fever, worsening pain, mucus, weight loss, or signs of dehydration. Do not stop a prescribed medicine without advice, but mention iron, bismuth, anti-inflammatory painkillers, and blood-thinning medicines when seeking care.

Seek urgent medical help for black tarry or sticky stool, visible blood, vomiting blood or material resembling coffee grounds, severe or persistent abdominal pain, fainting, confusion, or marked weakness. These features can indicate digestive bleeding or a serious illness.

Get prompt advice if you cannot keep fluids down, are passing very little urine, feel unusually dizzy, have a high fever, or develop a dry mouth with increasing thirst. Infants, older adults, pregnant people, and people with significant long-term illness can become unwell from fluid loss more quickly.

Ask: Does the stool look like food or medicine-related colour change, or could it be tarry bleeding? Could infection, intolerance, coeliac disease, thyroid activity, or bowel inflammation explain the pattern? Do I need stool tests, blood tests, or an examination, and how should I replace lost fluids?