Why Is Your Poop Black and Tarry?

What Black Stool Means and When to See a Doctor

What Is Black Poop?

Occasionally, poop can appear black and tarry, with a sticky texture. This may result from something harmless—like foods, supplements, or medications—or it can signal a serious medical problem.

Stool color normally varies from shades of brown to yellow or green, depending on diet, bile, and digestion. But black or bright red stool often suggests bleeding in the digestive tract. Because of this, it’s important to contact a doctor if your stool turns black, especially if it looks tarry.

Common Causes of Black Stool

Black stool can be linked to several conditions and substances:

• Internal bleeding in the digestive tract
• Medications or supplements such as iron or bismuth subsalicylate
• Dark-colored foods like licorice, blueberries, and dark leafy greens
• Activated charcoal supplements

Internal Bleeding and Melena

When blood is digested in the stomach or small intestine, stool can appear black, tarry, and foul-smelling. This condition is known as melena.

Potential causes of bleeding include:

• Peptic ulcers caused by H. pylori infection or NSAID overuse
• Gastritis or esophagitis (inflammation)
• Mallory-Weiss tears from forceful vomiting
• Esophageal or gastric cancers
• Esophageal varices linked to liver disease
• Acute hemorrhagic erosive gastropathy (erosion from alcohol, NSAIDs, or cancer treatment)

Melena is a serious symptom requiring medical evaluation. Doctors may test stool for blood and use imaging or endoscopy to find the source of bleeding. Treatment may involve stopping the bleed, replacing lost blood, and treating the underlying cause.

Ulcers and Black Stool

Peptic ulcers are one of the most common reasons for black stool. They develop when stomach acid damages the lining of the stomach or intestine.

Other symptoms may include:

• Burning stomach pain or heartburn
• Bloating and nausea
• Vomit that looks like coffee grounds
• Unexplained weight loss

Treatment often involves acid-reducing medications, protective agents for the stomach lining, and antibiotics if H. pylori is present.

Iron Supplements and Black Stool

Iron pills for anemia often cause stool to appear black or very dark green. This side effect is harmless, but stool should not appear sticky or tarry.

Other side effects of iron supplements:

• Constipation or diarrhea
• Nausea and heartburn
• Stained teeth with liquid forms

Always follow your doctor’s dosage instructions and report severe side effects.

Foods That Can Darken Stool

Certain foods and drinks may temporarily cause stool to turn black, including:

• Black licorice
• Blueberries
• Beets
• Dark chocolate cookies
• Blood sausage
• Dark beers and grape juice
• Foods with artificial coloring

The dark color usually resolves once these foods are no longer consumed.

Medications: Bismuth Subsalicylate

Medicines containing bismuth subsalicylate (such as Pepto-Bismol or Kaopectate) can turn stool black. This happens because bismuth reacts with sulfur in the digestive tract, forming bismuth sulfide.

The color change is harmless and fades within days of stopping the medication.

Cancer and Black Stool

Cancers of the esophagus or stomach may cause tumors to bleed, leading to black, tarry stool.

Warning signs may include:

• Difficulty swallowing
• Chest or stomach pain
• Severe indigestion
• Nausea or vomiting
• Unexplained weight loss
• Persistent fatigue

Treatment depends on cancer type and stage, often involving surgery, chemotherapy, or radiation.

Black Flecks in Stool

Sometimes stool isn’t fully black but contains black spots or flecks. These may be undigested food particles (like blueberry skins) or dried blood. If stool looks like coffee grounds, it may indicate older bleeding.

When to Call a Doctor

Seek immediate medical attention if you notice:

• Black, tarry stool with a strong odor
• Blood in stool or vomit
• Dizziness, fainting, or weakness
• Stomach pain or chest pain
• Unexplained weight loss

These symptoms may signal a life-threatening condition such as severe bleeding, ulcer complications, or cancer.

Takeaway

Black stool may be harmless—caused by diet, supplements, or medication—but it can also be a warning sign of internal bleeding or other serious conditions. Always contact your doctor if your stool is black, tarry, or foul-smelling.