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What Causes Black Stool?

Black, sticky stool can mean there’s too much iron in your diet. It could also be a sign of internal bleeding.
Four black stools
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Written by Andrew Le, MD.
Medically reviewed by
Therapeutic Endoscopy Fellow, MD Anderson Cancer Center, Houston, TX
Last updated March 26, 2024

Black stool quiz

Take a quiz to find out what's causing your black stool.

Black stool may be from dark foods and drinks (beets and dark beer), supplements like iron, or a sign of bleeding in the upper GI tract. If stool is black and has a bad odor, it is likely a sign of bleeding, from a peptic ulcer, gastritis, inflammation, colon polyps, or colon cancer. Call your doctor, who may recommend an endoscopy or colonoscopy to locate the problem.

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What is black stool?

Stool can be many shades of brown. But when it veers towards black, it can be a sign of a problem.

Black stool can be caused by blood in your gastrointestinal (digestive) tract. But it could also just mean you ate something red, maroon, or dark, like beets, blueberries, or black licorice. Dark beers and lagers can also make stool look black.

Certain supplements and medications, such as iron and Pepto-Bismol, are another reason for black stool.

When you notice black blood in the stool, it usually is from higher in your intestine (stomach or small bowel). It starts out red, but as it travels through your intestine, the hemoglobin in the blood turns black. Black blood in the stool usually also has a bad odor.

In the first day of life, newborns have black stool made up of amniotic fluid, skin cells, and other things ingested while in the womb. This is normal and changes to a tan color within a few days.

Pro Tip

People think: “Blood is always red!”—it’s not! Our intestines are very long. As blood travels down your intestine, from the upper to the lower portions, it is acted on by digestive enzymes and intestinal bacteria. This turns it black and tarry. —Dr. Shria Kumar

1. Peptic ulcer


  • Abdominal pain (usually in the center of your abdomen, usually does not move to your back or shoulder, and is worse when eating)
  • Black, tarry stool
  • Heartburn
  • Weight loss
  • Nausea or vomiting (sometimes with blood)
  • Avoidance of eating
  • Bloating and feeling full
  • Difficulty or pain with swallowing

A peptic ulcer, a sore in the lining of the stomach or the first part of your small intestine (the duodenum), which can bleed and cause pain after meals or on an empty stomach. The inflammation can be from an infection from the bacteria H pylori. Or it can be caused by medication, such as nonsteroidal anti-inflammatory drugs (NSAIDs).

If it’s caused by H pylori, you’ll be prescribed antibiotics to treat the infection. If NSAIDs are the cause, your doctor will consider lowering or changing what you are taking. Reducing stomach acid with a proton pump inhibitor (like Nexium and Prilosec) can help with healing.

2. Gastritis


Gastritis is an inflammation of the lining of the stomach. The stomach has a layer of mucus to protect it from the strong acids that break down foods. If that mucus lining has tears or is not healthy, the stomach can become inflamed.

Damage to your stomach lining can happen for a variety of reasons, including stress, an autoimmune response, or an infection. Other causes include NSAIDs, smoking, or drinking alcohol or eating foods that irritate the lining of the stomach. Inflammation can cause small amounts of bleeding, which can turn your stool black.

Treatment depends on the cause. If the gastritis is caused by smoking, stop smoking. If it’s caused by drinking, cut back on alcohol.

If it’s from taking NSAIDs, your doctor will likely recommend lowering the dosage or changing what you take. If the cause is an autoimmune response, you may need other medications and more follow-up.

3. Colon polyps


  • Black or bloody stool

Colon polyps are small growths in the colon. Polyps begin as benign (not cancerous) growths, but can develop into cancer over time. Usually, they do not have any symptoms, but sometimes, they can ooze small amounts of blood.

A colonoscopy can find polyps before they become cancerous. When they are found during the procedure, the gastroenterologist will remove them. This prevents them from turning into cancer.

Some people are more likely to form colon polyps because of their genetics. Other factors that are associated with polyps (and future colon cancer) are being overweight, smoking, and eating a lot of red meat and processed foods.

4. Colorectal cancer


  • Changes in bowel habits
  • Not feeling hungry
  • Weight loss
  • Black or bloody stool
  • Abdominal pain
  • Fatigue

Colon cancer and cancer of the rectum are sometimes described under the umbrella term “colorectal cancer.” Noncancerous polyps in the rectum can become cancerous over time, which is why regular colon screening with a colonoscopy is recommended. Colorectal cancer is the third most common cancer in men and women, according to the Centers for Disease Control and Prevention (CDC).

Colorectal cancers can be diagnosed at any age, but it usually affects people over 50. Obesity, a sedentary lifestyle, smoking, and alcohol use can increase your risk for colorectal cancer.

Colon cancer is usually treated with a combination of surgery and chemotherapy.

5. Constipation

Pro Tip

“Black tarry stool, like oil, and foul smelling”—this is blood! “Small, pellet like stool, but really dark”— this is more suggestive of constipation and iron supplementation. —Dr. Kumar


Constipation is when you have infrequent bowel movements and stool is very hard and dry. The stool may appear darkish or black. When you try to have a bowel movement, you may strain, or your stool may look like hard pellets. You may feel abdominal pain, cramping, or bloating.

Laxatives, good nutrition, and drinking a lot of fluids can all help with constipation. See a doctor if constipation doesn’t get better, if you have severe abdominal pain with it, or you see streaks of red blood or other unusual colors in your stool.

Other possible causes

A number of conditions can cause black stool, though they are less common. They include:

  • Variceal bleeding, which is bleeding from veins in the esophagus that can be from advanced liver disease (cirrhosis).
  • Mallory-Weiss tear, a tear in the mucous membrane of the esophagus, particularly after bouts of heavy coughing or repetitive vomiting.

When to call the doctor

Dr. Rx

Black stool can have a lot of causes. They can be uninteresting (iron supplementation, various foods, even alcohol) or more dangerous (bleeding). The biggest consideration is your health status and underlying conditions. If you have black stool, it’s important to discuss with your doctor. —Dr. Kumar

  • You are pregnant.
  • You recently started a new medication.
  • You are experiencing abdominal pain.
  • You are taking blood thinners, like warfarin (Coumadin).

Should I go to the ER for black stool?

You should go to the ER if you’re having any of the following symptoms:

  • You’re vomiting blood
  • You’re in severe pain
  • The bleeding is uncontrolled
  • You’re experiencing confusion or difficulty thinking
  • You feel lightheaded, faint, or dizzy
  • You’re having chest pain or shortness of breath
  • You are feeling dizzy and lightheaded


Don’t assume your dark stool is from your diet or constipation until you confirm it with your doctor. In some cases, your doctor may need to do an endoscopy or a colonoscopy (looking into your esophagus and stomach or your colon with a tube) or another procedure to check for tears, polyps, or bleeding in the colon or intestines.

Here are some over-the-counter (OTC) remedies that could help.

  • Iron Supplements: If your diet's a bit heavy on iron, a little balance might do the trick.
  • OTC Antacids: Peptic Ulcers Got You Down? A soothing warrior in the face of stomach issues, over-the-counter antacids can be a real hero.
  • OTC Anti-inflammatory Meds: For gastritis relief, your stomach lining might need a little tender love and care.
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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Black stoolsPosted November 12, 2023 by M.
Diarrhea over a week and then the black stools.
Therapeutic Endoscopy Fellow, MD Anderson Cancer Center, Houston, TX
Dr. Kumar is a gastroenterologist, who completed her fellowship at the Hospital of the University of Pennsylvania in Philadelphia. She received her undergraduate degrees in Religious Studies and Chemistry from New York University (2010) and graduated from the Albert Einstein College of Medicine (2014), where she was inducted into the Alpha Omega Alpha Honor Medical Society. She is completing her t...
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