If your stool appears black, you may be confused — and worried. But while black stool may be unusual, it’s not necessarily a cause for concern.
"Oftentimes, black stools are caused by medications or food and, as such, are harmless," says Paul Johnson, MD, a board-certified colorectal surgeon and surgical oncologist at Methodist Le Bonheur Healthcare in Memphis, Tennessee.
Still, black stool can sometimes signal a more serious issue. Here are the common culprits behind black stool and when to see a doctor.
4 Potential Reasons Your Poop Is Black
Stool color is primarily determined by the amount of bile, or digestive fluid, it contains. Bile starts out as a yellow-green but tends to turn brown as it's broken down by the enzymes in your digestive tract. Diet, medications, and health conditions can turn stool tan, red, yellow, black, and green.
Here are a few potential reasons your stool may be black.
1. You Eat a Lot of Dark-Colored Foods
Dark foods can turn your poop nearly black, especially if you've eaten them in great quantities (much more than typical serving size). Common culprits include black licorice, blueberries, beets, and blood sausage.
The natural compounds that give these foods their dark color can stain your stool, Dr. Johnson explains. Blueberries, for example, contain pigmented antioxidants called anthocyanins, which can give poop a darker brown shade.
Black poop is a potential side effect of certain dietary supplements, particularly iron supplements, says Janese Laster, MD, a board-certified gastroenterologist, internist, obesity medicine specialist, and nutritionist in private practice in Washington, DC.
If iron is the culprit, your stool will likely be a greenish or grayish shade of black. Dr. Laster says this is a normal side effect caused by the way iron pills are broken down in the gut.
Supplements that contain activated charcoal — which are sometimes touted as a remedy for gas and bloating — can also darken your poop. Activated charcoal is a black powder, and just like dark-colored foods, its midnight hue can stain your poop black.
3. You’re Taking Anti-Diarrheals
Black stool is a common side effect of over-the-counter anti-diarrheal medicines, which are used to treat digestive issues like heartburn, indigestion, diarrhea, and nausea.
The offender is bismuth subsalicylate, the active ingredient in many anti-diarrheal medications. “Bismuth subsalicylate can react with naturally occurring substances in your gastrointestinal tract and result in black or dark poop," Johnson explains. You might notice your tongue appears darker, too.
These are typical side effects that disappear after you stop taking the medication.
4. You Have a Gastrointestinal Bleed
In more serious cases, black stool can signal bleeding in the digestive tract. Doctors refer to this kind of black poop as melena, Johnson says, and it can signal bleeding in the stomach, esophagus, or small intestine caused by ulcers (open sores in the lining of the gut), cancer, or a tear in the lining of the gastrointestinal (GI) tract.
Johnson explains that melena is black instead of red because the blood has passed through the colon, where bacteria break down its hemoglobin (the protein that lends blood its scarlet hue). For this reason, it also usually has a tar-like texture.
Some people are more prone to this kind of internal bleeding, including those who take blood-thinning medications like warfarin or use nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, or naproxen sodium, Laster says. Blood thinners make it harder for your blood to clot, so a small tear or sore in the intestines that would normally heal just fine could lead to worrisome bleeding, Laster says. NSAIDs, on the other hand, can damage the inner lining of the GI tract, leading to ulcers in this lining that cause bleeding.
People who had gastrointestinal surgery or have mechanical heart valves (often used to replace diseased or damaged heart valves) are also at greater risk of melena, as are those with the following conditions:
Crohn's disease (a chronic digestive disease that causes inflammation and damage in the GI tract)
Many causes of black poop are harmless, but Johnson says it’s best to visit your doctor to rule out any serious issues, especially if your stool turns black more than once, is tarry, or has a very offensive odor.
Dark, smelly stool along with symptoms of melena warrant a trip to the emergency room, Laster says. These symptoms include, per Laster:
Pain in your abdomen, chest, or back
Nausea or vomiting (especially if the vomit is red or dark, like coffee grounds)
Diarrhea
Dizziness or lightheadedness
Heart palpitations
Shortness of breath
Your healthcare provider may run a series of tests to diagnose the cause of black stool, including a blood test, stool test, rectal exam, or an upper endoscopy (which uses a small tube with a camera attached to look inside your upper digestive tract), Laster says. A colonoscopy (an exam that uses a thin, flexible tube with a camera on the end to look inside your colon) or a computed tomography (CT) scan may also be used.
The Takeaway
Black poop is typically harmless and is often caused by eating dark-colored foods or taking certain medications or supplements.
In rare cases, black poop could be a sign of gastrointestinal bleeding, which is a serious issue that requires immediate medical attention.
Talk to your doctor if you notice black stool. Get help immediately if it comes with symptoms like a foul odor, nausea or vomiting, dizziness or weakness, pain, or shortness of breath.
EDITORIAL SOURCES
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Resources
Stool Color: When to Worry. Mayo Clinic. October 2024.
Ira Daniel Breite, MD, is a board-certified internist and gastroenterologist. He is an associate professor at the Icahn School of Medicine at Mount Sinai, where he also sees patients and helps run an ambulatory surgery center.
Dr. Breite divides his time between technical procedures, reading about new topics, and helping patients with some of their most intimate problems. He finds the deepest fulfillment in the long-term relationships he develops and is thrilled when a patient with irritable bowel syndrome or inflammatory bowel disease improves on the regimen he worked with them to create.
Breite went to Albert Einstein College of Medicine for medical school, followed by a residency at NYU and Bellevue Hospital and a gastroenterology fellowship at Memorial Sloan Kettering Cancer Center. Working in city hospitals helped him become resourceful and taught him how to interact with people from different backgrounds.
Kaitlin Ahern is a New Jersey–based health journalist and content strategist with over a decade of experience in lifestyle media and content marketing. She has held staff positions at Well+Good, Livestrong.com, Johnson & Johnson, and Parents.com. She is a graduate of the S.I. Newhouse School of Public Communications at Syracuse University.
