Black stool, known medically as melena, is typically a sign of bleeding in the upper gastrointestinal (GI) tract, which includes the esophagus, stomach, and the first part of the small intestine. The black, tarry appearance results from the blood being partially digested and chemically altered by stomach acid as it moves through the digestive system. While this symptom warrants immediate attention, it is important to first distinguish between true melena and pseudo-melena, which is a benign blackening caused by ingested substances.
Non-Bleeding Causes of Dark Stool
In many cases, the black color is not caused by blood but by substances consumed shortly after drinking, a phenomenon called pseudo-melena. The most common culprit is bismuth subsalicylate, the active ingredient in many over-the-counter stomach remedies often taken to soothe an upset stomach or hangover. When the bismuth compound interacts with sulfur naturally present in the digestive tract, it forms bismuth sulfide, which temporarily darkens the stool and sometimes the tongue.
Iron supplements are another frequent cause of dark stool, as the unabsorbed iron turns black as it passes through the system. Certain dark foods and drinks can also cause a temporary color change, including black licorice, blueberries, and dark beers or stouts.
A key difference between pseudo-melena and true melena is the consistency and odor. Stool blackened by diet or medication is simply dark black, whereas true melena is sticky and tarry, often having a distinctly foul odor due to the breakdown of blood products. If the black stool is not tarry and resolves within a few days of stopping the suspected food or medication, it is likely pseudo-melena. However, any persistent black stool should be medically evaluated.
How Alcohol Triggers Gastrointestinal Bleeding
When black stool is true melena, it means there is bleeding high up in the digestive tract, and alcohol is a significant risk factor for several causes of this bleeding. Alcohol is a direct irritant to the mucosal lining of the stomach, which can lead to acute erosive gastropathy, or inflammation and erosion of the stomach lining. This damage can create hemorrhagic lesions that bleed into the stomach, resulting in black stool.
Alcohol also significantly increases the risk of peptic ulcer disease, which involves open sores in the lining of the stomach or duodenum. Alcohol can exacerbate existing ulcers and interfere with the healing process, making them more prone to bleeding. The risk of upper GI bleeding is compounded when alcohol is consumed alongside nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen.
Forceful retching or vomiting associated with heavy alcohol consumption can trigger a Mallory-Weiss tear, which is a longitudinal laceration near the junction of the esophagus and the stomach. These tears are caused by a sudden, severe increase in intra-abdominal pressure and are a common cause of acute upper GI bleeding.
For individuals with underlying liver disease often associated with excessive alcohol intake, the pressure in the blood vessels around the esophagus can increase, leading to enlarged, fragile veins called esophageal varices. These varices can rupture and cause severe, life-threatening bleeding.
Recognizing Emergency Symptoms
Black stool that is tarry and foul-smelling is a sign of bleeding, but certain accompanying symptoms indicate a medical emergency that requires immediate attention. Signs of significant bleeding include feeling dizzy, lightheaded, or fainting, which signal a drop in blood pressure. Acute blood loss can quickly lead to systemic distress.
A rapid heart rate (tachycardia) is another sign that the body is attempting to compensate for blood loss. Also look for severe abdominal pain or the vomiting of blood, known as hematemesis. Vomited blood may appear bright red or look like dark coffee grounds, indicating partial digestion by stomach acid. These symptoms suggest an active hemorrhage and necessitate an emergency room visit.
Medical Assessment and Treatment Options
A medical assessment for suspected upper GI bleeding begins with evaluating the patient’s stability through vital signs and blood tests. Blood work helps determine the degree of blood loss, checking for anemia and the body’s ability to clot. The definitive diagnostic tool is an upper endoscopy, also called an esophagogastroduodenoscopy (EGD).
During an EGD, a flexible tube with a camera is passed down the throat to visualize the esophagus, stomach, and duodenum to locate the source of bleeding. If a bleeding site is identified, the physician can perform therapeutic interventions immediately, such as injecting medication, applying heat to cauterize the vessel, or placing a clip to seal the bleed. Treatment also involves medications like proton pump inhibitors (PPIs) to reduce stomach acid production, which helps a bleeding ulcer or erosion heal. In severe cases, specialized procedures or fluid and blood transfusions may be necessary to stabilize the patient.