What does black stool indicate?

Black poop doesn’t always mean there is an underlying medical concern. There are some foods, supplements, and medications that can cause your stool to look black. But sometimes black poop may be a sign of a condition that you and a healthcare provider should address.

If your stool is black and sticky, smells bad, or is accompanied by other digestive symptoms, that may signify an issue that you need to talk to your healthcare provider about. 

Causes of Black Poop

Typically, stool is some shade of brown. Depending on several factors, such as what you eat or what medical conditions you have, poop color can be a color other than brown. For instance, there are several things that can make your poop look black.

Foods

Some dark-colored foods and beverages can make your poop look black. These include:

• Black licorice
• Blueberries
• Blood sausage

Beets and foods with dark red food coloring can also make your stool look reddish.

If food is what's causing your poop to be darker, there’s no cause for medical concern. Your poop will return to a normal color once the food is out of your system.

Iron Supplement

You can have black poop when taking an iron tablet, a type of iron supplement. Iron helps the body make red blood cells. You can get iron through the food you eat, but you may need to take an iron tablet to treat or prevent anemia, a condition that most often develops when you don't have enough iron to make an adequate number of red blood cells.

And while black poop is normal with iron tablets, stomach pain is not. You'd want to contact a healthcare provider if you are experiencing stomach pain when taking iron pills.

Medications

Some medications may cause black stool.

Medications that contain the ingredient bismuth can turn poop black. This includes the medication bismuth subsalicylate, sold under brand names like Pepto-Bismol and Kaopectate. Bismuth subsalicylate works against diarrhea, heartburn, nausea, and upset stomach.

Activated charcoal can also make you have black poop. This is charcoal that has been heated so that pores develop within the charcoal. Activated charcoal can be used to treat poisoning because the charcoal's pores can trap chemicals. If you've swallowed a poison, a healthcare provider may administer activated charcoal by mouth so that the substance can trap the harmful chemicals in your body.

Blood 

Bleeding in your upper gastrointestinal tract may cause your poop to look black. This is because as the blood is digested through your tract, it gets darker. The bleed can be coming from any part of the upper gastrointestinal tract, such as the esophagus, stomach, or the first part of the small intestine.

Blood starts out red, but as it moves through your body and interacts with enzymes in the digestive tract, it turns black. The medical term for this is melena. When poop is black because it contains blood, it is also often foul smelling and tarry.

There are many reasons why you may have blood in your stool that’s making your poop look black. Bleeding that makes your stool black-colored may be caused by:

• Gastritis: This is an inflammation of the stomach lining. When left untreated, areas of the stomach lining can get worn-away and cause bleeding.

• Peptic ulcer: This is a sore inside your stomach or the first part of your small intestine (duodenum) that can cause bleeding if it wears away your stomach lining.

• Varices: Veins in your esophagus, the tube that connects your mouth to your stomach, can become enlarged and irritated. If the veins rupture, they can cause bleeding. 
• Angiodysplasia of the gastrointestinal tract: These are abnormally-formed blood vessels that can weaken and rupture, which causes bleeding.
• Esophagitis: This is swelling of the lining of your esophagus, which can become irritated and bleed.
• Mallory-Weiss tear: Intense coughing or vomiting can cause small tears in your esophagus, which bleed.
• Tumors: Both cancerous and non-cancerous tumors in your gastrointestinal tract can weaken the tract's lining and cause bleeding.

A bleed in the lower gastrointestinal tract, like the rectum or anus, would cause bright red blood in your stool since the blood did not have to travel through the entire tract.

Related Symptoms

Depending on what's causing your poop to be black, you might experience symptoms in addition to the change in stool color.

For instance, along with black poop, you might experience constipation and diarrhea when taking a iron supplement. If you're taking iron supplements in large doses, you might also develop nausea and vomiting.

If taking activated charcoal, you can experience constipation. If taking bismuth subsalicylate, nausea and diarrhea are possible.

If you are experiencing gastrointestinal bleeding, your stool may be tarry and smell foul. Any other symptoms you may have alongside black stool depend on the reason for the bleeding. While symptoms vary, some common ones include:

• Dizziness
• Fainting
• Abdominal pain
• Nausea 
• Indigestion
• Tiredness
• Pale skin
• Shortness of breath

Getting a Diagnosis

After asking about your symptoms and any food, supplements, or medications you are taking, a healthcare provider will most likely perform a physical exam where they will listen to your abdomen with a stethoscope and tap on different parts of your abdomen. The provider may order tests to help reach a diagnosis, especially if they suspect a gastrointestinal bleed. These tests may include: 

• Stool test: You will receive a container to catch and store your stool for testing. This test may find blood in your stool that you can't see with the naked eye.
• Blood test: This looks at your blood count and may help determine how extensive a bleed may be and whether you have anemia.
• Endoscopy: There are several types of endoscopy, which is when a tube with a tiny camera at the end explores parts of your gastrointestinal tract to find the cause of the bleeding.
• Gastric lavage: A tube is placed in your stomach through your nose or mouth, and the stomach contents are emptied. A healthcare provider can then look for the spot that is bleeding.
• Imaging tests: Computed tomography (CT) scans, X-rays, or other imaging tests can help your healthcare team determine the cause of the bleeding.

Getting Treated

If you're passing black poop, treatment will depend on what's causing it. If your stool is black due to food, supplements, or medications, your healthcare provider may talk to you about changes you can make to prevent it from happening in the future.

If a bleed is causing your darker stool, the bleed will need to be stopped. If a healthcare provider finds a bleed during an endoscopy, they might be able to stop the bleed during the procedure. They can do this by injecting medication or administering a laser to the bleed site. They can also use a band or clip to close off affected blood vessels.

If a bleed doesn't stop, you might need surgery to gain better access to the affected area so that providers can more successfully stop the bleed.

Should You Be Concerned About Black Poop?

If you see that your stool is black, consider what you've recently eaten. Also consider whether you are taking an iron pill, bismuth subsalicylate, or activated charcoal. Black poop is an expected symptom in these cases, but you can still reach out to a healthcare provider to discuss the effect.

If you can’t trace black poop back to something you ate or took, it’s a good idea to talk to your healthcare provider. That's especially true if the poop is tarry and smells badly, which are additional signs that bleeding is causing the darker stool.

If you notice blood in your stool, you should contact a healthcare provider. You should also seek medical care if you vomit blood or feel dizzy or lightheaded.

A Quick Review

It can be alarming to see black stool. Oftentimes the color change can be due to eating dark-colored food or starting a new supplement or medication. However, black stool can sometimes be a sign of bleeding within the upper part of your gastrointestinal tract. If you have black stool—especially if it is tarry and smells particularly bad—reach out to a healthcare provider. They can determine why your stool is black and, if it's black from blood, where the bleed is happening. Once they determine why your stool is black, they can provide any necessary treatment.

Black or tarry stools with a foul smell are a sign of a problem in the upper digestive tract. It most often indicates that there is bleeding in the stomach, small intestine, or right side of the colon.

The term melena is used to describe this finding.