Black Diarrhea: What It Means & When It’s Serious

Key takeaways:

• Black diarrhea is frequently a sign of gastrointestinal bleeding, especially from the upper GI tract, and requires urgent medical care.
• While some causes of black diarrhea can be less serious, such as that caused by certain foods or medications, it’s important to know when you should go for medical advice to avoid a potentially life-threatening condition.
• Learning how to address and prevent black diarrhea can help you with managing your symptoms, but if you are experiencing black diarrhea or black tarry stools, you should be seen as soon as possible by a healthcare provider.

The appearance of black diarrhea can understandably be quite alarming. The color of your stool can give you important clues about the condition of your gastrointestinal (GI) tract. Back stools may indicate bleeding or can be caused by certain medication or foods.

Let’s take a closer look at the common causes of black diarrhea, when this might point to something serious, how to manage or treat it, and when to reach out for medical care.

Is black diarrhea normal?

Black diarrhea is not a normal condition. If you are having black diarrhea, this is something that requires attention.

In many cases, the black color comes from digested blood, which makes the blood appear black in color. Black diarrhea that is caused by gastrointestinal bleeding is usually coming from the upper part of your GI tract. Keep in mind that certain foods, supplements, and some medications can also cause black stools, so it’s important to be able to tell the difference between harmless causes and those that need medical evaluation.

Common causes of black diarrhea

There are several potential causes of black diarrhea. These range from relatively harmless to serious. Below are some common reasons you may be experiencing black diarrhea;

Gastrointestinal bleeding

Bleeding from your stomach or upper intestines is one of the most common and serious causes of black diarrhea. The black color comes from blood that has been digested by the acids in your stomach, resulting in a black tar-like appearance known as melena.

Peptic (stomach) ulcers, gastritis (stomach inflammation), or esophageal varices (varicose veins of the esophagus) are common causes of this type of bleeding​.

Iron supplements

Taking iron supplements can cause your stools to turn black. This black color is a harmless side effect. The excess iron in the supplement that is not absorbed by your body can darken your stool. Although this is not typically a cause for concern, you should get medical advice if you have additional symptoms like stomach pain or vomiting.

Certain foods

Eating foods containing dark pigments, such as blueberries, black licorice, or foods with artificial black coloring, can sometimes result in black diarrhea. These cases are usually temporary and resolve completely once the food passes through your digestive system​.

Medications

Medications containing bismuth subsalicylate (brand name Pepto-Bismol) can cause your stool to turn black.

This is a well-known side effect and typically goes away completely once you have stopped taking the medication. If your stool continues to appear black several days after you have taken the last dose, you should consult with your physician.

What black diarrhea may mean based on appearance, consistency, or another symptom or condition

You can get clues about the underlying cause of black diarrhea by looking at both the stool’s appearance and evaluating any associated symptoms:

Black, tar-like diarrhea

A black, tar-like appearance of the stool most often means digested blood in your stool. This is a sign of upper gastrointestinal bleeding, which could result from a peptic (stomach) ulcer or esophageal varices (varicose veins of the esophagus).​

Black, watery or liquidy diarrhea

Watery, black diarrhea suggests there has been a rapid transport of blood through your digestive tract. This could also mean that you have a gastrointestinal infection or possibly a severe irritation​.

Black, oily diarrhea

Oily black diarrhea can be a sign your digestive system is not properly absorbing fats. This condition is called malabsorption, and can occur in disorders such as chronic pancreatitis, an inflammation of the pancreas,​

Black-green diarrhea

Sometimes diarrhea can appear as a black-green color. This can be related to bile production, a greenish digestive fluid produced by your liver and stored in your gallbladder. Also, certain medications and supplements like iron​ can cause your stool to appear black-green.

Black flecks in diarrhea

Small black flecks could indicate small amounts of blood that have clotted in your stool. This is generally less concerning than if you were to see a large quantity of black stool but this still requires medical attention to get at the underlying cause.​

Black diarrhea with a foul odor

A foul odor that comes with black diarrhea could be a sign of gastrointestinal bleeding or infection. Black diarrhea always warrants follow up medical care, especially if you are experiencing other symptoms, such as fever or abdominal pain.

Black diarrhea accompanied by vomiting

If you have black diarrhea along with vomiting, it’s possible you have bleeding in your gastrointestinal tract. This could also be caused by an infection. Both situations require that you get urgent medical care​.

Black diarrhea accompanied by stomach cramps

Stomach cramps with black diarrhea could mean gastrointestinal bleeding or an infection like bacterial gastroenteritis. You should get a medical evaluation as soon as possible.​

Black diarrhea after taking Pepto Bismol

Black stools are a well-known side effect of Pepto Bismol, an over-the-counter medicine used to treat an occasional upset stomach, heartburn, and indigestion. This color change is usually harmless. If the black diarrhea continues even after you have stopped the medication or is accompanied by other symptoms, such as fever or abdominal pain, get medical advice​.

Black diarrhea after drinking alcohol

Alcohol is a well-known irritant to the lining of the stomach. Heavy alcohol consumption that severely irritates the stomach could lead to bleeding and black diarrhea. The chronic use of alcohol can also damage your liver, which can lead to multiple digestive problems.​

Black diarrhea that occurs during pregnancy

While rare, black diarrhea during pregnancy could be related to iron supplements taken as part of your prenatal vitamins. This could also be due to gastrointestinal bleeding. If you are pregnant and experience black diarrhea, you should consult your physician to rule out a serious cause.

When to see a doctor about black diarrhea

You should see a doctor if:

• Your black diarrhea continues for more than a day or two.
• You have other symptoms like dizziness, stomach pain, or vomiting.
• There is a foul odor or visible blood in your stool.

You should go to the emergency room if:

• You are having severe abdominal pain or you are vomiting blood.
• In addition to black diarrhea, you have signs of shock, such as mental confusion, a rapid heartbeat, lightheadedness, or fainting.
• You have a history of gastrointestinal bleeding in the past and you are now experiencing black diarrhea.

Questions to ask your doctor about black diarrhea

To make the most of your doctor's visit, consider asking the following questions:

1. What is causing my black diarrhea?
2. Do I need any diagnostic tests, such as a stool test or endoscopy to see if there is bleeding?
3. What treatments are available for my condition?
4. How can I prevent this from happening again?

How to stop or treat black diarrhea

Treatment for black diarrhea will depend on the underlying cause, but here are some common approaches:

Rehydration

Diarrhea often leads to fluid loss, so it’s important to drink plenty of fluids. Oral rehydration solutions or electrolyte drinks such as some sports drinks or PediaLyte™ can help replace those lost fluids and prevent you from becoming dehydrated​.

Medications

If an underlying condition like a peptic (stomach) ulcer or infection is the cause, medications such as proton pump inhibitors (PPIs) that decrease stomach acid, or antibiotics to fight the infection may be prescribed to manage your symptoms.​

Stopping the bleeding at the source

If your physician believes you have active upper gastrointestinal bleeding, you will likely need to undergo urgent diagnostic tests, such as an endoscopy, to diagnose the cause of the bleeding and stop it.

An endoscopy is a procedure done under anesthesia or sedation, depending on your circumstances. In many cases, the gastroenterologist can pinpoint the source of the bleeding and use clips, injections, or thermal procedures to stop it.

Avoiding trigger foods and medications

If food or medications like iron supplements are the cause, avoiding these triggers may help stop black diarrhea.​

How to prevent black diarrhea

Taking steps to maintain your digestive health can help prevent episodes of black diarrhea in the future:

Regular health checkups

Routine health exams can help catch conditions that could cause gastrointestinal bleeding before they become severe​. Based on your age, history, and doctor’s recommendations, these exams may include routine preventative procedures such as a stool test for blood or other regular tests.

Avoid excessive alcohol

Limiting your alcohol intake can reduce your risk of gastrointestinal bleeding and liver damage, as both can cause black diarrhea​.

Monitor medication use

Be mindful that medications like iron supplements or Pepto Bismol can cause black stool. Always follow the dosage recommendations and consult your doctor if your symptoms persist​.

Frequently asked questions: black diarrhea

Can dehydration cause black diarrhea?

Dehydration itself doesn’t cause black diarrhea, but if diarrhea continues and you don’t get enough fluids, dehydration can happen.

What foods or drinks cause black diarrhea?

Some foods like blueberries or black licorice, and drinks or other processed foods containing artificial black dyes can cause temporary black diarrhea​. If the black diarrhea continues for a day or two after stopping the food or drink, you should consult with your healthcare provider.

Is black diarrhea a sign of food poisoning?

While food poisoning can cause diarrhea, black diarrhea is usually a sign of gastrointestinal bleeding rather than food poisoning​.

Managing black diarrhea

Black diarrhea is often a sign of a more serious condition, especially when it’s related to gastrointestinal bleeding. While some causes of black diarrhea, such as certain foods or medications, are harmless, it’s important to know when you should get medical advice.

If you’re experiencing black diarrhea, especially if it is accompanied by other symptoms like stomach pain, vomiting, or dizziness, you should see your healthcare provider urgently to determine the cause and get appropriate treatment.

General Medicine follows a strict editorial process, including using real experts to write our articles, vetted primary sources, fact-checking, a secondary medical review, and updates as necessary. This article was medically reviewed and fact checked by Dr. Marjorie Bravard, MD.

Sources

American College of Gastroenterology. “Peptic Ulcer Disease.” American College of Gastroenterology, https://gi.org/topics/peptic-ulcer-disease/. Accessed 23 Oct. 2024.

American Liver Foundation. “Cirrhosis: Severe Scarring of the Liver.” American Liver Foundation, https://liverfoundation.org/about-your-liver/how-liver-diseases-progress/cirrhosis-severe-scarring/. Accessed 23 Oct. 2024.

Centers for Disease Control and Prevention. “About Alcohol Use.” Centers for Disease Control and Prevention, U.S. Department of Health and Human Services, https://www.cdc.gov/alcohol/about-alcohol-use/index.html. Accessed 23 Oct. 2024.

National Institute of Diabetes and Digestive and Kidney Diseases. “Gastrointestinal Bleeding.” National Institute of Diabetes and Digestive and Kidney Diseases, U.S. Department of Health and Human Services, https://www.niddk.nih.gov/health-information/digestive-diseases/gastrointestinal-bleeding. Accessed 23 Oct. 2024.

National Institute of Diabetes and Digestive and Kidney Diseases. “Upper GI Endoscopy.” National Institute of Diabetes and Digestive and Kidney Diseases, U.S. Department of Health and Human Services, https://www.niddk.nih.gov/health-information/diagnostic-tests/upper-gi-endoscopy. Accessed 23 Oct. 2024.

Veterans Health Administration. “Gastrointestinal Bleeding: Symptoms, Diagnosis, and Treatment.” Veterans Health Library, U.S. Department of Veterans Affairs, https://www.veteranshealthlibrary.va.gov/Encyclopedia/3,40442. Accessed 23 Oct. 2024.