It’s a terrifying moment. You look down into the toilet bowl and see something that looks like road tar—thick, sticky, and jet black. It’s not just "darker than usual." It’s visceral. Honestly, your first instinct is probably to panic or, conversely, to ignore it and hope it was just those blueberries you ate yesterday. But understanding what is black tarry stool a symptom of is actually one of the most important health checks you can do for your digestive system.
In the medical world, we call this melena. It’s distinct from just "dark poop." Melena has a specific texture and a very particular, metallic, foul odor that you won't soon forget. It happens because blood has been digested. By the time it travels through your stomach and small intestine, the acid and enzymes have broken down the hemoglobin, turning it from bright red to that signature midnight black.
The Most Likely Culprit: Upper GI Bleeding
If you're wondering what’s going on, the most frequent answer involves the upper gastrointestinal (GI) tract. This includes your esophagus, stomach, and the first part of your small intestine, the duodenum. When blood leaks here, it spends a lot of time hanging out with stomach acid. That chemical reaction is what creates the tarry look.
Peptic ulcers are the leading cause of this. Specifically, a sore on the lining of your stomach or your duodenum. You might think ulcers are just from "stress," but that’s an old-school myth. Most ulcers come from a bacteria called Helicobacter pylori (H. pylori) or from overusing common painkillers like ibuprofen, naproxen, or aspirin (NSAIDs). If you've been popping Advil for a nagging back injury and suddenly see black stool, there is your smoking gun.
It’s not always a slow leak, either. Sometimes it’s a full-blown medical emergency.
Gastritis and Esophageal Issues
Sometimes the stomach lining just gets incredibly irritated and inflamed—this is gastritis. Alcohol is a huge trigger here. A heavy night of drinking can irritate the stomach lining enough to cause small amounts of bleeding.
Then there are the more serious structural issues. Esophageal varices—enlarged veins in the tube connecting your throat and stomach—can leak or rupture. This is most common in people with significant liver disease or cirrhosis. When these veins bleed, it’s often heavy and dangerous. Another possibility is a Mallory-Weiss tear, which is a literal tear in the lining of the esophagus, usually caused by violent vomiting or coughing.
It’s Not Always Blood: The "False" Melena
Before you spiral into a Google-induced panic, check your medicine cabinet and your recent meals. Not everything black is blood.
- Iron Supplements: This is the big one. If you’re taking iron for anemia, your stool will turn dark green or black. It’s usually not "tarry" or sticky, though. It’s just colored differently.
- Bismuth Subsalicylate: Think Pepto-Bismol. The bismuth reacts with trace amounts of sulfur in your saliva and digestive tract to turn things black. It’s harmless, but it looks scary.
- Food: Did you eat a whole bag of black licorice? Or maybe a pint of blackberries? Beets usually turn things red, but blueberries and dark chocolate can sometimes darken things enough to cause a double-take.
How do you tell the difference? Smell and texture. True melena is sticky—like actual tar—and it smells uniquely metallic and rotten. Iron-induced stool just smells like, well, stool.
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The Connection to Cancer
We have to talk about it because it's what everyone fears. Yes, black tarry stool can be a symptom of stomach cancer or esophageal cancer. These tumors can bleed into the digestive tract. However, it is rarely the only symptom. Usually, there’s also unexplained weight loss, persistent indigestion, or a feeling of being full after eating very little.
According to the American Cancer Society, while colorectal cancer usually causes bright red blood (hematochezia), if the cancer is high enough in the colon—like the ascending colon—the blood can occasionally darken. But generally, black and tarry means "higher up" in the system.
When This Becomes An Emergency
Don't wait. If you see black tarry stool and you also feel dizzy, lightheaded, or like you might faint, get to an ER. This suggests you are losing blood fast enough that your blood pressure is dropping.
Medical professionals will likely use the Glasgow-Blatchford Score (GBS). This is a tool doctors use to decide if a patient with an upper GI bleed needs a blood transfusion or immediate surgery. They look at your hemoglobin levels, your heart rate, and whether you have other conditions like heart failure or liver disease.
Diagnosis and What Happens Next
If you go to a doctor—which you should—they won’t just take your word for it. They’ll likely perform a fecal occult blood test (FOBT) to confirm there is actually blood in the sample.
The gold standard for finding the source is an endoscopy. They'll sedate you and slide a camera down your throat to see exactly what’s leaking. It sounds unpleasant, but it's incredibly effective. They can often "clip" or cauterize the bleed right then and there.
Actionable Steps To Take Now
If you are currently experiencing this, here is your checklist.
- Stop taking NSAIDs immediately. If you’ve been taking ibuprofen, aspirin, or naproxen, switch to acetaminophen (Tylenol) for pain until you talk to a doctor. NSAIDs inhibit the enzymes that protect your stomach lining.
- Recall your intake. Write down everything you ate or drank in the last 48 hours, including supplements and Pepto-Bismol.
- Check for "Red Flag" symptoms. Are you short of breath? Pale? Is your heart racing? If yes, call for help.
- Schedule an appointment. Even if you feel fine, melena is a signal that something is wrong. A slow-bleeding ulcer can eventually lead to severe anemia or a perforation (a hole in your stomach).
- Request an H. pylori test. If it turns out to be an ulcer, make sure they test for the bacteria. If you don't kill the bacteria with antibiotics, the ulcer will just keep coming back.
Don't ignore your body's "check engine" light. Black tarry stool is a distinct physical sign that requires a professional opinion to rule out serious internal issues.