What should you know about grayish-black stool?

Stool colour changes when food moves quickly through the bowel or when pigments from food, supplements or medicines pass through. Iron products and some stomach medicines can darken stool. Black stool that is sticky, tarry or unusually foul-smelling is different: digested blood from the stomach or upper bowel can create this appearance. Gastritis, Helicobacter Pylori Infection and Peptic Ulcer are among the conditions a clinician may consider, particularly with upper-abdominal discomfort, burning, nausea or weakness.

A single uncertain colour change is not enough to identify a cause. Note the appearance, recent foods and medicines, and whether the change repeats.

If the stool is dark after starting iron or a bismuth-containing medicine, check its information leaflet and contact a pharmacist if the change is unexpected. Do not stop a prescribed medicine without advice. Arrange medical review promptly for repeated grayish-black stool, especially if you have abdominal pain, light-headedness, unusual tiredness or take medicines that affect bleeding. A clinician may examine you and decide whether blood testing or digestive investigations are needed.

Seek emergency care for black tarry stool with fainting, severe weakness, confusion, rapid breathing, severe abdominal pain, vomiting blood or vomit resembling coffee grounds. These combinations can indicate significant digestive bleeding. Do not wait for the next bowel movement if you feel seriously unwell.

Tell the clinician when the colour began, whether it was sticky or tar-like, what medicines and supplements you take, and whether you have pain, vomiting, dizziness or changes in energy.