Black Tarry Stools: Causes, Symptoms, Treatments (Science Based)

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Black Tarry Stools: Causes, Symptoms, Treatments
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Tarry stools are feces that have dark red or dark black color. Black tarry stools can occur because of consuming certain foods and supplements or due to bleeding in your upper gastrointestinal (GI) tract. Your stools can appear dark green, black or discolored because of eating foods like licorice, green leafy vegetables, or when taking iron supplements. Black tarry stools that have a foul smell are often caused by internal bleeding in the upper part of your GI system (medical term is melena).

Sometimes, you may also notice signs of bleeding in the lower GI tract if there is bright red blood on stool.

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Even though upper gastrointestinal bleeding is a serious cause of pooping black tarry stool, it is rarely life-threatening. Ulcers in your stomach, GI infections, or inflammation can cause stool to turn from a normal brown color to dark green or black.

Regularly pooping black stool is not considered normal and you should speak to your doctor to rule out anything too serious.

What is the Normal Stool Color?

Your normal stool color should be light to dark brown. Your liver produces bile which is required for digestion and gives stool its normal brown color. The bile contains bilirubin which turns the digested food that travels through the digestive system to light or dark brown color.1

There are many factors that influence the color of your stool. For example, one of the symptoms of a gallbladder problem is clay-colored stool.

The Encyclopaedia Britannica reports that stool is made up of 25% solid matter and 75% water. A healthy digestive system will produce normal feces that are brown. Other issues with your digestion like diarrhea, internal bleeding, or inflammatory conditions can result in bloody stools, black poop, or greenish colored stool.2

Black Tarry Stool – Related Symptoms

Thankfully, passing the occasional black tarry stool doesn’t necessarily mean that there is something wrong with your gastrointestinal system.

Dr. John P. Cuhna on eMedicineNet reports that the color of normal poop can range from light yellow to nearly black. If black, tar-like stool is the result of a digestive issue, then you may have one or more of the following symptoms:3

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Recognizing symptoms that accompany black stool can help to identify the root cause.

Dark Green Tarry Stool

Sometimes, very dark green stool may resemble black tarry feces in the toilet bowl. In many cases, green pigments from certain foods that can interact with digestive bile and result in very dark, almost black, poop.

According to Dr. Benjamin Wedro on MedicineNet, certain vegetables can make bowel movements look almost black. For example, large amounts of kale, cabbage, or spinach can cause dark green stool. However, your stool should return to its normal brown color after a day or two.4

Doctors from the Mayo Clinic report that green poop can be caused by diarrhea. Because food passes through the digestive system too quickly, bile can’t turn feces brown and they come out looking green or yellowish.5

Black Tarry Stools and Melena

The publication Clinical Methods says that melena describes stools that look black and tarry because of gastrointestinal bleeding.

Doctors say that melena is the name for stools that are jet black and have a distinct stickiness to them. The color of stool, whether is it jet-black poop or stools that have red blood on them can indicate where bleeding occurs.6

Blood that is old turns black and upper intestinal bleeding will cause black stool or black vomit.

Sometimes, sticky black stool that isn’t caused by internal bleeding is referred to as “false melena.” This describes stool that is black and tarry because of a chemical reaction to certain supplements.

Because it can be difficult to distinguish between melena (black, bloody stool) and “false melena,” (black stool with no blood) you should always see a doctor if you pass black tarry poop.

Common Causes of Black Tarry Stools

The two main reasons why you could start having black, sticky bowel movement are due to something you consumed or gastrointestinal bleeding. Let’s look first at foods and supplements that can turn your poop dark green or black.

Causes of Black Tarry Stools: Foods, Supplements, or Medications

Iron supplements

Having bowel movements that look like black sticky lumps of stools are often a side effect of taking iron supplements.

If you have anemia due to iron deficiency (iron deficiency anemia) your doctor may prescribe iron supplements to boost your hemoglobin levels.

The National Heart, Lung, and Blood Institute reports that taking iron supplementation for iron deficiency anemia can result in dark stools. Iron tablets can also cause constipation, stomach irritation, and heartburn.7

Doctors also say that iron deficiency anemia can also result in upper GI bleeding and black, tar-like poop.7

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Researchers from the National University Hospital in Singapore report that iron supplementation is also a reason for “false melena.” In these cases, black poop without blood usually looks very dark green.8

Medications

Some medications have the side effect of causing tarry looking stool without the presence of blood (false melena).

Dr. Benjamin Wedro on MedicineNet reports that some anti-diarrhea medications can result in black tarry diarrhea. The reason for blackened poop is due to a chemical called bismuth. Your stool should return to its normal color when you cease taking the medication.9

Interestingly, medications containing bismuth can also be one of the many reasons for bowel movements that have pale-colored stool.

If you have started having very dark brown or green tarry stools after taking medication, you should speak to your doctor.

Dark-colored foods

Having discolored bowel movements where poop is extremely dark or black-looking could be due to dark-colored foods.

One of the foods that causes black poop, or false melena, is licorice. Many people consume licorice due to its many health benefits. However, the World Journal of Gastrointestinal Surgery reports that black pigments in licorice can turn bowel movements black.10

Researchers also report that you should avoid taking black licorice together with warfarin (a popular blood thinner). When consumed together, licorice and warfarin can increase the risk of upper GI bleeding which may result in dark tarry stools.

There are other foods can turn your poop color black. For example, the University of Florida reports that blueberries can cause poop to look black.27 Also, beets and tomatoes can cause red-colored stools.11

Activated charcoal

Dark green or black tarry bowel movements could last for a day or two if you take activated charcoal.

Doctors from the Mayo Clinic say that activated charcoal can help to relieve digestive upset. A common, but not serious, side effect of taking activated charcoal is passing black poop. This can be accompanied by diarrhea and, on rare occasions, stomach pain.12

Black Tarry Stool Caused by Gastrointestinal Issues

The presence of old blood will darken your stools and make them appear black and sticky. The unusual color and texture of stool can help doctors diagnose where bleeding is coming from.

Dr. Parswa Ansari who specializes in colon and rectal surgery says that black feces that smell bad can indicate upper GI bleeding. However bleeding in the small bowel or right colon can also cause black tarry poop. It is worth noting that bright red blood in your bowel movement can be a sign of bleeding in the lower intestinal tract or anus.13

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Peptic ulcers

Ulcers in the lining of the stomach or small intestine can cause gastrointestinal bleeding and turn your poop black and tarry.

Gastroenterologist Dr. Erwin Biecker reports that peptic ulcers are a common reason for internal bleeding. Apart from causing nausea, upper abdominal pain, and fatigue, gastrointestinal ulcers can cause black, tarry stools.14

The first signs of a peptic ulcer are usually dull abdominal pain after eating, heartburn, or burping. Dr. John P. Cuhna on eMedicineHealth says that if the ulcer becomes severe, it can cause internal bleeding. This can cause tarry black bowel movements or vomiting that has “coffee grinds” in it.15

Inflammatory bowel disease (IBD)

Inflammatory bowel disease covers a number of conditions that can affect the digestive tract and cause black tarry-like poop. The 2 most common inflammatory gastrointestinal conditions that cause black stool are Crohn’s disease and ulcerative colitis.

Crohn’s disease. According to expert in gastroenterology, Dr. Lori Kam, Crohn’s disease can result in upper GI Bleeding. Crohn’s disease can cause sores and ulcers anywhere in the digestive tract. This type of IBD can result in bouts of black, tar-like stool or episodes of pooping stool along with red blood.16

Crohn’s disease can also result in passing fatty stool, urgent need to poop, frequent stomach gurgling, and mouth sores.

Ulcerative colitis. Researchers from the Cleveland Clinic say that ulcerative colitis causes bloody diarrhea. Ulcerative colitis usually affects the colon or large intestine. Bowel movements may be painful and urgent with signs of mucus in poop.17

However, in some occasions, ulcerative colitis can cause bleeding higher in the GI tract that causes melena (black tarry stools).18

Gastritis

Inflammation of your stomach lining is called gastritis and can result in occasional black tarry bowel movements. Gastritis can be caused by viral infections, bacterial infections, or irritants in the stomach.

According to researchers from the Harvard Medical School, severe inflammation in the digestive tract can cause bleeding. This can cause passing black stuff during a bowel movement and bloody vomiting. Other gastritis symptoms can include lower abdominal pain, nausea, and bloated stomach along with discomfort.19

Colonic polyps

Colonic polyps are small, usually benign, growths in the colon that can cause your poop to turn a black color.

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Doctors from the Mayo Clinic report that polyps often cause no symptoms at all. However, if the small growths cause bleeding, you may have poop with bloody streaks or pass stools that are dark or black. Polyps in the colon can also cause abdominal cramping, constipation, diarrhea, and low hemoglobin count.20

Because bleeding from your anus is also one of the signs of colon cancer, you should see your doctor if you have rectal bleeding or black stools.

Mallory-Weiss tear

Forceful vomiting or chronic alcohol consumption can cause a tear in your upper GI tract called a Mallory-Weiss tear.

Dr. Gurvinder Rull on Patient.info reports that the rupture usually happens at the upper part of the stomach and causes bleeding. The result can be black tarry bowel movements that have a foul smell. The blood loss can also cause dizziness and upper abdominal pain under the ribs.21

However, violent coughing, a hiatus hernia, or lifting heavy items can also cause a Mallory-Weiss tear and passing black-colored stool.

Usually, the tear heals by itself and the stool should return to normal after a few days when the GI bleeding has stopped.

Diverticulosis

Diverticulosis is when small bulges in your colon and lower part of your intestines form into pouches called diverticula. There are many complications of diverticulosis, some of which can result in dark tarry stools.

According to Dr. Rohan C. Clarke from the Department of Gastroenterology at JPS Health Systems Hospital, diverticulosis can cause melena. Because the reason for black tarry stools can be difficult to diagnose, doctors may need to perform a colonoscopy.22

Other complication of diverticulosis can include pain under the ribs, rectal bleeding, diarrhea, or signs of diverticulitis.

Colorectal, esophageal, or stomach cancer

In rare occasions, having black tarry stool or diarrhea can be a sign of a tumor in the gastrointestinal tract.

Cancerous growths can cause internal bleeding in the upper part of the intestines. Dr. Elwyn C. Cabele, who is an oncology consultant, says that some of the symptoms of gastric cancer can include black stool, fullness after eating, rectal bleeding, unexplained weight loss, or difficulty swallowing.23

It’s important to remember that the main causes of black bowel movements that have a tarry consistency are usually less sinister.

Other Causes of Black Tarry Stool

There are some, less common, reasons for passing tar-like stool because of internal bleeding.

Liver disease

Your liver is located in the upper right side of your abdomen and liver disease can affect your esophagus. According to researchers from Johns Hopkins Medicine, liver disease can cause blood vessels in your esophagus to enlarge and rupture. This will result in melena – the name for black, tarry stools.24

Barrett’s esophagus

Another condition that can affect your esophagus and cause tarry black stools is Barrett’s esophagus which is a serious complication of GERD. Doctors from the Mayo Clinic say that complications of Barrett’s esophagus are stools that are black and tarry or bloody, chest pain, and vomit that looks like coffee grinds.25

How to Treat Black or Tarry Stool

In order to treat black tarry bowel movements you need to address their underlying medical cause. If the black, tarry stools that give off an offensive smell are caused by bleeding, doctors will arrange for surgery or prescribe medication to treat the root cause.

In some cases iron supplements, certain foods or certain medications can cause black stools. Your stool should return to its normal brown color after you stop consuming these products.

If you are concerned about black tarry stools after antibiotics or taking iron supplements, you should speak to your doctor. In some cases, your doctor could recommend another way to treat iron deficiencies.

It is also important to remember that pooping dark green stool after eating vegetables isn’t a sign of anything ominous. They are a good source of fiber, vitamins, nutrients, and antioxidants that keep you and your digestive system healthy.

When to See a Doctor

Passing the occasional dark green or black stool probably isn’t anything to worry about. Your stool should return to its normal brown color after a day or two. However, changes in bowel habits like dark poop or pooping black tarry stool longer than a few days need to be evaluated by a doctor.

Doctors from the Cleveland Clinic recommend seeing a doctor in the following circumstances:26

  • Black, sticky stools that have a foul odor
  • Noticing streaks of blood on any color of stool
  • Abdominal pain and passing bloody diarrhea
  • Constipation and signs of anal leakage
  • No abdominal pain relief after passing stool

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