Reason for dark brown stool

Stool colour changes as bile pigments are altered during digestion. A dark brown shade can be normal, especially after eating darker foods or when stool has moved more slowly through the bowel. Reduced fluid intake can make stool firmer and sometimes darker. The colour alone does not diagnose a liver problem. Liver or bile-flow illness may instead occur with yellowing of the eyes or skin, pale stools, dark urine, nausea, or pain. Dark, sticky, tar-like stool is different from ordinary dark brown stool and can indicate bleeding higher in the digestive tract.

Notice whether the change is brief or continues, and record food, medicines, bowel frequency, consistency, and other symptoms. Drink fluids regularly unless a clinician has restricted them, and include fibre gradually if constipation is present. Do not rely on colour alone to judge hydration; urine colour and thirst can add useful context. Contact a clinician if the change persists without an obvious explanation or keeps recurring. Bring a list of medicines and supplements, including products containing iron or bismuth.

Seek urgent care for black tarry stool, visible blood, dizziness, fainting, marked weakness, severe abdominal pain, repeated vomiting, yellow skin or eyes, or inability to keep fluids down. Dark stool with signs of dehydration or heat illness also needs prompt attention.

Does this colour look different from bleeding-related stool? Could my medicines, diet, constipation, or liver function be involved? Which changes should prompt immediate care?