Passing dark blood in stool: what you should know

Passing dark blood in stool should be medically assessed, especially when the stool is black and tar-like or you feel unwell. Dark red or maroon blood may come from bleeding farther along the bowel, while black, sticky stool can indicate digested blood from higher in the digestive tract. The appearance alone cannot show the cause.

Blood can turn dark as it travels through the digestive system. Bleeding may be linked to irritation, an ulcer, inflammation, bowel pockets, or a growth, but many bowel conditions can overlap in appearance. Crohn's disease and ulcerative colitis can inflame the bowel and cause bleeding; diverticular disease can also bleed. Iron tablets, bismuth-containing medicines, and some dark foods can change stool colour without bleeding, although they should not be used to dismiss new or repeated symptoms.

Tell a clinician whether the stool was black and sticky, dark red, or maroon, and whether the change happened once or keeps returning. Mention abdominal pain, diarrhoea, constipation, vomiting, fever, weight change, tiredness, and every medicine or supplement you take.

If you notice dark blood, contact a healthcare professional promptly for advice, even if the amount seems small. Keep a note of the colour, texture, frequency, and associated symptoms. Do not stop prescribed medicines without advice, but tell the clinician if you use blood thinners, aspirin, anti-inflammatory painkillers, iron, or bismuth. Assessment may include an examination, blood tests, and further bowel or stomach investigations depending on your symptoms.

Seek emergency care now for black tar-like stool or heavy bleeding, particularly with dizziness, fainting, confusion, marked weakness, pale or clammy skin, rapid breathing, severe abdominal pain, or vomiting blood. These signs can occur when bleeding is significant or your circulation is being affected. Do not drive yourself if you feel faint. Repeated dark stools, worsening pain, or new bleeding while taking a blood thinner also needs urgent medical advice.

Ask what the stool colour and texture suggest, whether any medicine or supplement could explain it, and which tests are appropriate. You can also ask whether you need to change anti-inflammatory painkillers or blood-thinning treatment, what symptoms should send you to emergency care, and when you should arrange follow-up if the bleeding stops.