What does it mean when my stool is black?

Black, tarry stools—medically termed melena—typically indicate upper gastrointestinal (GI) bleeding. The dark, sticky, foul-smelling appearance results from the digestion of hemoglobin as blood passes through the stomach and small intestine. Common causes include peptic ulcers, gastritis, esophageal varices, Mallory-Weiss tears, or erosive esophagitis. Less commonly, melena may arise from bleeding in the proximal small bowel.

It’s important to distinguish true melena from pseudomelanosis—benign discoloration caused by certain foods (e.g., black licorice, blueberries, activated charcoal) or medications (e.g., iron supplements, bismuth subsalicylate). However, these do not produce the characteristic tarry consistency or strong odor associated with actual GI bleeding.

Melena is a red-flag symptom requiring prompt medical evaluation. Even small volumes of blood (as little as 50–100 mL) can cause visible melena, and significant bleeding may occur before hemodynamic instability becomes apparent. Evaluation typically includes a thorough history, physical exam (including orthostatic vital signs), complete blood count, coagulation studies, and urgent upper endoscopy to localize and potentially treat the source.

If melena is accompanied by symptoms such as dizziness, syncope, tachycardia, hypotension, or hematemesis (vomiting blood), this suggests acute, potentially life-threatening hemorrhage—and immediate emergency care is warranted.