Constipation and dark poop: what it can mean

Stool colour can change after iron tablets, bismuth-containing medicines, or deeply coloured foods. Constipation can make stool harder and less frequent, but it does not by itself explain every dark colour. Black, sticky, tar-like stool with a strong unusual smell can indicate digested blood from higher in the digestive tract.

Look at the colour in good light and consider when the change began. Tell a clinician about iron, pain-relief medicines, supplements, diet changes, dizziness, or vomiting. Do not stop a prescribed medicine without advice.

Keep a note of stool appearance, bowel frequency, recent foods, and medicines. Drink fluids regularly if you have no fluid restriction, increase fibre gradually, and avoid forceful straining. If the stool is truly black or tar-like and you cannot explain it by a known medicine or food, contact a healthcare professional promptly rather than treating constipation alone.

Go to urgent care for black tar-like stool, red blood, vomiting blood or coffee-ground material, faintness, marked weakness, fast heartbeat, severe abdominal pain, or repeated vomiting. Seek a routine review for ongoing constipation, recurring dark stools, unexplained weight change, or symptoms that do not settle after a suspected food or medicine change.

Could my iron, bismuth, supplements, or pain medicine explain the colour? Does the stool need testing? What bowel treatment is safe with my other medicines and health conditions?