Black or Dark Green Stool: What Dark Poop Means (Science Based)

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Black or Dark Green poop

Noticing black stool after a bowel movement may cause you to wonder what has turned your poop very dark. Usually black or dark green stool is caused by eating certain foods or due to gastrointestinal (GI) bleeding. Some foods like licorice, green leafy vegetables, or taking supplements can turn your poop very dark green or black. If bleeding of the upper GI is to blame, you may pass black and tarry stools that could have a foul smell. Bleeding of the colon or small intestine can also cause darkened stool with bright red blood on the stool.

It’s important to remember that black stool due to blood in the stool doesn’t usually cause a life-threatening condition. Health issues like GI inflammation, infections, or peptic ulcers can all result in bleeding that can turn stool black. However, you should never self-diagnose signs of GI bleeding, and you should not ignore regularly passing black stools. If you notice black tarry stool with other signs of bleeding, you should speak to your doctor, especially if passing black or darkened stool is accompanied by abdominal pain, lightheadedness, vomiting, or fainting.

If you are wondering what it means when your poop is black, you will find the answers in this article. In some cases, you will also learn how to treat black poop or avoid black bowel movements.

How Stool Is Formed and What Considers to Be a Normal Poop

Stool is formed as food passes through your digestive system and is broken down by the digestive enzymes and bile. Organs like your pancreas, liver, and gallbladder are all involved in absorbing nutrients from food.

Dr. Jennifer Robinson on WebMD says that bile, red blood cells, waste, and fat combine to form stool that is normally brown. Contractions move stool through your colon which is now mostly waste and bacteria. The stool ends up in the rectum where it waits until you have a bowel movement.1

There is actually a lot that the consistency and color of your poop can tell about your health. According to the Encyclopaedia Britannica, normal poop is made up of 25% solid matter and 75% water. The normal brown color of stool is due to bacteria affecting the bile in your gut. Issues with your intestines or stomach can cause brown stool to turn dark red, tarry, or even black. Other signs of digestive disorders are passing greasy stool, constipation, or diarrhea.2

What Does It Mean When Your Poop Is Black?

Black tarry stool or dark green stool that looks black is often accompanied by other symptoms related to the digestive dysfunction. Dr. John P. Cuhna on eMedicineNet says that the normal stool color can be anything from light yellow poop to almost black. Color changes in stool due to digestive issues may also cause any of the following:3

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  • Abdominal pain and cramping caused by an ulcer or inflammation
  • Nausea and vomiting because of blood in the intestines
  • Dizziness or even fainting because of a loss of blood
  • Itching in the rectum
  • Pain when passing stool
  • Black tarry stools that have traces of fresh blood on it

The above symptoms along with signs of gastrointestinal bleeding should be evaluated by a medical professional.

What is Melena?

Melena is dark stool from digested blood. Doctors say that melena refers to blood pigments or dark blood products that turn stool or vomit black.4

Not all black stool is referred to as melena because not all the reasons for very dark poop is related to gastrointestinal bleeding. Therefore, “false melena” is a black bowel movement that doesn’t have traces of old blood in it. If your black feces are from iron supplements or certain medications, your stool becomes black because of an interaction between the supplements and digestive enzymes, and this is not a case of melena.

If you start having black diarrhea or passing black tarry stools, it is always best to see your doctor for a checkup. This makes sure that your black poop is really false melena and not something more sinister.

Dark Green Poop

It is also important to remember that sometimes what you think as a black bowel movement is actually very dark green stool. Black green poop often happens when green pigments from certain foods interact with bile causing your poop to look almost black.

Dr. Benjamin Wedro on MedicineNet says that you can pass dark green poop after eating green leafy vegetables like spinach, kale, or cabbage. This is nothing to worry about, and your poop should return to a normal brown color when you stop eating the particular vegetable.5

Also, a stomach bug can cause green diarrhea because food passes through your digestive system too quickly. This means that bile in your intestines can’t turn feces brown.

Black Stool Causes

Let’s look in more detail at the various causes why your poop is black.

Dark Black Stool Due to Foods, Supplements or Medications

Black stool without blood is very common and is usually nothing to worry about. The black stool only means that chemical or compounds in certain foods have affected the color of your poop.

Iron supplements

A common reason for passing black tarry stools is taking iron supplements. Oral iron supplements are a common way to prevent or treat the symptoms of iron deficiency anemia.

The journal PLoS One reports that blackened stools are a common side effect of taking iron supplements. Treating anemia with oral iron therapy can also cause other digestive upset including:

Some of the best natural sources of iron to include in your diet include:

  • Seafood like oysters, clams or mussels
  • Beef
  • Chicken
  • Green leafy vegetables when taken together with vitamin C

Black foods

Certain black-colored foods can make your poop appear dark green to black, especially if eaten in large quantities.

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Some people consume large amounts of licorice for its anti-inflammatory and antioxidant properties. According to the World Journal of Gastrointestinal Surgery, pigments in black licorice could mean that you could start having black bowel movements. This results in poop that is classed as “false melena.”6

Scientists also noticed that a combination of black licorice and warfarin could also result in upper GI bleeding. This would cause black tarry stool because of blood in the bowel movement. Therefore, doctors don’t recommend taking anti-coagulants as well as consuming licorice.6

Researchers from the University of Florida report that blueberries could also cause poop to appear black and tarry.7

Medications

Taking medications can cause “false melena” and result in passing black stool without blood in it.

One type of medication that darkens poop is medications containing bismuth to relieve digestive upset. Doctors say that bismuth doesn’t only turn your stool black, but it can also darken your tongue. The color of your bowel movements should return to normal when you stop taking medication containing bismuth.5 Sometimes, bismuth itself can cause upper GI bleeding which results in melena.8

Activated charcoal

Dark green or black poop is often a side effect of taking activated charcoal to relieve digestive problems.

Doctors from the Mayo Clinic say that black bowel movements are common when using activated charcoal.9

Black Stool Due to Gastrointestinal Bleeding (Lower or Upper GI Bleeding)

When your poop is black, it can mean that you have bleeding somewhere in your gastrointestinal system. Often the color of your stool can indicate to a doctor where the bleeding is coming from. For example, black tarry stools usually mean that bleeding is higher up the GI tract. Whereas, bright red bloody poop can mean a tear or fissure closer to your rectum.

According to Dr. Parswa Ansari from Lenox Hill Hospital in New York, black feces can also occur when intestinal bleeding is from the small bowel or right colon.9

Peptic ulcers (gastric ulcers)

An ulcer in your upper digestive tract caused by the Helicobacter pylori bacteria can cause black tarry stool along with abdominal pain.

According to Dr. John P. Cuhna on eMedicineHealth, gastric ulcers on the stomach lining usually cause cramping pain below the ribs. The stomach aches usually start a few hours after eating. However, if the ulcer is severe, it can start to bleed, which will cause black sticky stools. This could also cause vomiting that looks like coffee grounds.10

There are many natural remedies for stomach ulcers you can try that help to relieve burning feeling in your stomach. However, you should see a doctor if you have signs of upper or lower GI bleeding or vomiting up blood.

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Gastritis

Passing black stool in a bowel movement could mean that you have gastritis or inflammation of your stomach lining. Doctors from the Medical University of South Carolina say that gastritis can cause bleeding in your upper GI tract and stomach pain after eating.11

Ulcerative colitis

Passing darkened stool with blood in it could mean that you have an inflammatory bowel condition like ulcerative colitis. Dr. Melissa Conrad Stöppler on MedicineNet says that dark red stools are often associated with ulcerative colitis. This type of inflammatory bowel disease (IBD) can also result in severe digestive upset.12

Crohn’s disease

Crohn’s disease is another inflammatory bowel disease that can cause your poop to go black. Dr. Lori Kam on MedicineNet says that Crohn’s disease can cause bleeding high in the GI tract. This will result in black tarry poop that may sometimes have streaks of blood on it.13

Colonic polyps

One of the reasons your stool is black and tarry is because of small harmless growths in your digestive tract called polyps. Researchers from the National Institute of Diabetes and Digestive and Kidney Disease say polyps in the colon can cause upper or lower GI bleeding. This can mean that blood in your stool becomes black as it passes through your digestive system.14 Your doctor will remove all polyps discovered during a bowel examination, and they will be sent to a pathologist to be tested, as cancer can start in some types of polyps.

Mallory-Weiss tear

Melena can be caused by a rupture in your upper gastrointestinal tract and is called a Mallory-Weiss tear. The book Clinical Examinations reports that sticky black stools can occur if there has been bleeding of upper GI origin, and one of its causes can be Mallory–Weiss tears. This condition can be caused by extreme vomiting or long-term consumption of too much alcohol.15

According to the National Organization for Rare Disorders (NORD), in many cases, bleeding caused by Mallory-Weiss tear will stop without treatment. If the bleeding persists, treatment will be needed to seal the tear.23

Tears or inflammation of the esophagus

Your esophagus is also part of your upper GI tract that can cause black bloody stool if inflammation or a tear causes severe bleeding. The cause of inflammation can be chronic acid reflux, excessive vomiting, or a hiatal hernia. The journal Deutsches Ärzteblatt International says that melena is a symptom of many esophageal conditions.16

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Small intestinal diverticulosis

Diverticulosis is when pockets form in your small intestine or colon. When one or more of these pockets become inflamed or infected, the condition is called diverticulitis. Expert in gastroenterology Dr. Rohan C. Clarke says that symptoms of diverticulosis include black bowel movements (melena), passing blood along with stools, abdominal cramping, or diarrhea.17 

Cancer in the colon, stomach or esophagus

Black diarrhea or passing black stools could be a symptom of cancer that is affecting the gastrointestinal tract. Oncology consultant Dr. Elwyn C. Cabebe says that some of the symptoms of cancer of the colon, stomach, or esophagus are black stools, indigestion, passing bloody stools, and/or unintended weight loss.18

Other Causes of Black or Very Dark Stool

There are some other reasons for passing black feces in a bowel movement. Some of these are:

  • Liver disease. Researchers from Johns Hopkins Medicine say that liver disease can cause esophageal varices. These are large blood vessels in your esophagus that can become enlarged and rupture. If they bleed, the internal bleeding in your stomach will cause black tarry stools.19
  • Barrett’s esophagus. This condition happens with chronic gastroesophageal reflux disease (GERD). In severe cases, Dr. Bhupinder Anand on MedicineNet says that Barrett’s esophagus can cause stools to become black or maroon.20

How Black Stool is Treated

Black tarry stools can mean a medical emergency if there is chronic intestinal bleeding that becomes severe. Doctors usually treat black feces that contain blood by stopping the bleeding. This may be done surgically or with medication.

In cases where peptic ulcers or GI inflammation is causing bleeding that turn stool black, doctors may prescribe antibiotics or antacids to treat the infection. It is good to remember that some medication for gastrointestinal issues can also turn your stool black.

If you have black or dark green stool without blood in the stool, you can take some steps to reduce the occurrences of pooping dark stool. For example, drinking plenty of water and getting enough fiber will help keep your digestion working properly.

However, it’s important to remember that very dark green stools that are caused by green leafy vegetables don’t pose a health risk. In fact, you will boost your immune system naturally by eating nutrient-rich vegetables.

If iron supplements are causing digestive upset like pooping dark stool or causing abdominal cramping, you should speak to your doctor. Possibly changing the supplements or the dose may help to reduce gastrointestinal discomfort.

When to See a Doctor

Doctors from the Mayo Clinic say that in most cases, changes in stool color don’t indicate any serious health problem with your intestines. It’s normal for poop to be different shades of brown or even be very dark on occasion.21

According to doctors from the Cleveland Clinic, you should see your doctor if you notice symptoms of digestive upset along with changes in the color of your poop. Some of these include:22

  • Black or dark maroon stools, especially if accompanied by a bad smell.
  • Passing bright red blood with your stool.
  • Bloody diarrhea.
  • Abdominal discomfort that isn’t relieved by having a bowel movement.

Read my other related articles:

Medical Sources

  1. WebMD. Your digestive system.
  2. Britannica. Feces.
  3. eMedicineHealth. Stool color changes.
  4. MedicineNet. Medical definition of melena.
  5. MedicineNet. Stool color, changes in color, texture, and form.
  6. World J Gastrointest Surg. 2010 Jan 27; 2(1): 30–31.
  7. UFHealth. Bloody or tarry stools.
  8. WebMD. Bismuth.
  9. MayoClinic. Charcoal,
  10. eMedicineHealth. Peptic ulcer.
  11. MUSC. Gastritis.
  12. MedicineNet. Stool color & texture changes.
  13. MedicineNet. Inflammatory bowel disease.
  14. NIDDK. Symptoms & causes of colon polyps.
  15. NCBI. Hematemesis, melena, and Hematochezia.
  16. Dtsch Arztebl Int. 2008 Feb; 105(5): 85–94.
  17. Medscape. Small intestinal diverticulosis clinical presentation.
  18. Medscape. Gastric cancer clinical presentation.
  19. HopkinsMedicine. Common characteristics of liver
  20. MedicineNet. Barrett’s esophagus.
  21. MayoClinic. Stool color: when to worry.
  22. ClevelandClinic. Stool changes.
  23. NORD. Mallory Weiss Syndrome.
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