Sudden black, tar-like stools, medically termed melena, often signal internal bleeding in the stomach or upper intestine, according to a 2021 study. While some foods or supplements can cause temporary darkening, this texture and smell usually indicate a serious issue like ulcers or inflammation. Prompt medical evaluation is crucial, especially with accompanying symptoms like dizziness or vomiting blood.Sudden black, tar-like stools, medically termed melena, often signal internal bleeding in the stomach or upper intestine, according to a 2021 study. While some foods or supplements can cause temporary darkening, this texture and smell usually indicate a serious issue like ulcers or inflammation. Prompt medical evaluation is crucial, especially with accompanying symptoms like dizziness or vomiting blood.