What should you know about dark green and black stool?

Bile normally changes as it passes through the gut. When stool moves quickly, it can retain a green shade. Leafy vegetables and food colouring may have a similar effect. Iron, bismuth products, and certain medicines can darken stool without bleeding.

Pay attention to texture as well as colour. Black stool that is tarry, sticky, shiny, or unusually foul-smelling can indicate blood digested higher in the gut. Stomach inflammation, Helicobacter pylori infection, or a peptic ulcer may be part of the medical assessment, but a colour description cannot establish a diagnosis.

Record what you ate and any iron, bismuth, or new medicine before the change. If the stool becomes normal after the suspected trigger is gone, continue to observe it. Do not discontinue prescribed treatment on your own.

Arrange a clinician review if black or green-black stool repeats, remains unexplained, or comes with stomach discomfort, nausea, or a change in bowel habits. Testing can help distinguish pigment from blood.

Go to urgent care for black tarry stool with faintness, marked weakness, breathlessness, vomiting blood, severe abdominal pain, or a racing heartbeat. Repeated black stools deserve prompt review even when pain is absent, because digestive bleeding may not cause strong discomfort at first.

Ask whether the stool’s colour and texture suggest a food or medicine effect, or whether bleeding needs checking. Mention any ulcer history, indigestion, pain, nausea, iron use, stomach medicines, and symptoms such as dizziness or unusual tiredness.