Black stools

Category: Digestive & Abdomen · All digestive symptoms

What it can feel like

Black stools that are tarry and sticky (called melaena) usually mean blood has been digested during its passage through the gut, pointing to bleeding in the stomach or upper bowel. This is different from the harmless darkening caused by iron tablets, and it needs same-day assessment.

Possible causes

A symptom can have many causes, and most are not serious. The lists below group conditions this symptom can be associated with — common causes first. They are possibilities to discuss with a clinician, not a diagnosis.

Common causes

Black stools can be associated with iron supplements and bismuth-containing remedies, which darken the stool without blood being present — the stool is usually normal in consistency rather than tarry.

Other possible causes

True tarry black stools can be associated with stomach or duodenal ulcers, inflamed stomach lining, enlarged veins in the gullet in liver disease, and tumours — bleeding that can be significant even when you feel well.

Red flags — when to seek help promptly

Black, tarry stools — assess the same day, urgently if you feel unwell
Black stools with vomiting blood, dizziness or fainting
Black stools in someone taking blood thinners or anti-inflammatory painkillers
Black stools with pale, sweaty skin or a racing pulse

What a clinician may do

Emergency assessment includes pulse and blood pressure, blood tests and a blood count, and usually a camera examination of the stomach (gastroscopy) to find and often treat the bleeding point. A blood transfusion is given if the blood count has fallen significantly.

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Frequently asked questions

How can I tell iron-tablet stools from melaena?

Iron makes stools dark green-black and firm, but formed and not sticky. Melaena is tarry, sticky, glossy and distinctively foul-smelling. If there is any doubt — particularly with pain, vomiting blood or feeling faint — treat it as bleeding and seek help.

Why is a stomach camera needed so quickly?

Because treatment can often be delivered through the camera — sealing or clipping a bleeding ulcer — and finding the source guides everything after. Timing depends on how unwell you are and how much blood has been lost.

Related symptoms — Digestive & Abdomen

Abdominal pain Bloating Blood in the stool Change in bowel habit Constipation Diarrhoea

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Please note: This page is educational information about a symptom. A symptom alone cannot diagnose any condition, and the causes listed here are possibilities, not a diagnosis. If you are worried about a symptom — especially one that is new, severe, getting worse or not going away — please see your own clinician, who can examine you and arrange tests. In an emergency, call your local emergency number.