Black Stool: Causes, Symptoms, and When to See a Doctor

Melena: Black, Tarry, Foul-Smelling Stool

Indicates upper GI bleeding (proximal to ligament of Treitz). Blood digested by gastric acid → black color.

Common Causes

• Peptic ulcer disease (H. pylori, NSAIDs) – stomach or duodenum
• Esophageal varices (portal hypertension, cirrhosis)
• Gastritis / erosive gastropathy (alcohol, NSAIDs, stress)
• Mallory-Weiss tear (forceful vomiting)
• Vascular malformations (Dieulafoy lesion, angiodysplasia)
• Malignancy (gastric/esophageal cancer)

Non-Bleeding Causes (False Melena)

• Iron supplements
• Bismuth subsalicylate (Pepto-Bismol)
• Black licorice, blueberries, beets
• Activated charcoal

Associated Symptoms (Suggesting Significant Blood Loss)

• Weakness, dizziness, syncope
• Tachycardia, hypotension
• Shortness of breath
• Hematemesis (vomiting blood/coffee grounds)

Urgency

Melena with hemodynamic instability = medical emergency. Call 911 / go to ER.

Melena without alarm symptoms → urgent outpatient evaluation (GI consult, EGD).

Prevention

• Limit NSAIDs; use PPI if chronic NSAID needed.
• H. pylori test-and-treat.
• Alcohol moderation.
• Manage liver disease to prevent varices.