What should you know about constipation and dark stool?

Hard stool itself does not reliably explain black stool. Dark green or brown stool can follow foods, while iron tablets and some medicines can darken it. Black, sticky, tar-like stool with a strong unusual smell may indicate bleeding higher in the digestive tract. Constipation may occur at the same time because stool is moving slowly, but the two symptoms should not be assumed to share one harmless cause.

Look at whether the stool is simply dark brown or truly black and tarry. Note recent iron, bismuth-containing products, foods, and medicines, and do not stop prescribed treatment without advice. Drink regularly and avoid straining, but do not rely on fibre or laxatives to explain away black stool. Contact a clinician promptly if the colour is new, repeated, or uncertain, especially if you feel unwell.

Seek emergency care for black tar-like stool with dizziness, faintness, weakness, vomiting blood, severe abdominal pain, fast breathing, or confusion. Prompt assessment is also needed for repeated black stools, visible blood, or worsening constipation with vomiting and a swollen abdomen. A clinician may review medicines, examine you, and arrange tests to find the cause.

Tell the clinician when the dark stool started, whether it was sticky or tarry, and how often it occurred. Bring a list of iron, pain, stomach, and other medicines, plus details of abdominal pain, dizziness, vomiting, and your bowel pattern.