Black and watery stool: what it can mean

Bleeding from the stomach or the first part of the small intestine can make stool black, sticky or tar-like as blood is digested. Loose or watery stool may occur alongside this, although diarrhoea can also have a separate cause. Gastritis and a peptic ulcer are possible digestive causes; Helicobacter Pylori Infection can contribute to ulcer disease. Iron tablets, bismuth-containing medicines and some dark foods can also make stool look black without bleeding. Colour alone cannot distinguish these causes.

If the stool is genuinely black rather than dark brown, contact a clinician promptly and describe when it began, how many episodes occurred, and whether it was sticky or tar-like. Mention iron, bismuth, anti-inflammatory painkillers, blood thinners and recent antibiotics. Do not stop a prescribed medicine without advice. Keep drinking small amounts of fluid if you can, but avoid alcohol and avoid taking anti-diarrhoeal medicine until a clinician has considered bleeding.

Seek emergency care now for fainting, marked dizziness, confusion, cold clammy skin, severe abdominal pain, vomiting blood or material resembling coffee grounds, rapid worsening, or repeated black stools. These can indicate significant blood loss or dehydration. A person who is pregnant, older, taking a blood thinner, or managing a serious medical condition should seek advice without delay.

Ask whether the appearance could be melaena, whether your medicines or supplements matter, and which tests may identify bleeding or infection. Ask how to maintain hydration and which pain relievers are safer while the cause is being assessed.