Black Stool: Causes, Diagnosis And Treatment

Taking a look in the toilet bowl after doing a major one may seem disgusting, but it is necessary. It is the only way to tell if there is a change in the ‘gift’ your bowels give you (your poop).

If you notice black stool, understand that it is not normal. Something is causing your poop to change from the normal brown color to black.

This post explains the possible causes of black stool ranging from mild to severe and how they are diagnosed and treated.

Causes Of Black Stool

As stated earlier, black stools are never normal. Some of the causes are things you eat that turn up in your poop, others are medical conditions that require urgent treatment. The most common causes of black stool are as follows:

1. Dark Foods


Foods that have darker pigments – black, dark blue, dark green, may end up darkening the color of the stool. This is because there is no other way for the body to get rid of these pigments, so they are dumped in your stool.


Examples of such foods that cause black poop are –

  • Blueberries
  • Black licorice
  • Dark chocolate
  • Beets
  • Cranberries
  • Purple juice
  • Prunes
  • Dark-green leafy vegetables such as spinach and kale

If you have consumed any of these and you noticed your poop turned black, you may have found the cause. These foods aren’t harmful, and you can keep taking them but if the black stools bother you, then you may have to avoid these foods.

You may want to be sure that the cause of your black stools is the food you are ingesting. The best thing to do is to avoid these foods for a few days and observe your stool. If it remains dark/ black, then you may have something else going on that is unrelated to your diet.

However, if your stools revert to their normal color, it means that the blackening of your stool was due to your diet. There is no cause for alarm in this situation.

2. Medicines


Another very common cause of black stools is Iron supplements or Iron containing medication. The Iron ingested undergoes certain chemical reactions in the gut leading to black discoloration of the stools. This is entirely normal; in fact, it is expected.

When you start taking Iron-containing medications, most doctors will inform you of this well-known side effect of blackened stools.

Another popular stool darkening medicine is Pepto-Bismol or bismuth-containing drugs. Black stool with the use of any of these medicines is no cause for worry.

Once again, if you are convinced of something else going on, you can discontinue the medications and observe your poop.

Analgesics like Aspirin, Ibuprofen and other NSAIDs (Non-Steroidal Anti-Inflammatory Drugs) can cause black stools but in a more worrisome manner. Prolonged use of these drugs can damage the inner lining of the stomach and cause bleeding. When this blood mixes with poop, it turns black.

If you have been using these NSAIDs for a long period for conditions such as chronic pain and arthritis and have recently developed black stools, you may be bleeding in your gut. Please see your doctor as soon as possible for further evaluation.


3. Gastro-Enteritis


Gastroenteritis is the inflammation of the stomach and small intestines usually due to an infection. The infection causes the gut to be sore (inflamed) and some amount of blood is released which then ends up in the stool.

It is not a common cause of black stools and the infection would have to be very severe. Gastroenteritis more commonly causes nausea, vomiting, diarrhea, abdominal cramps, fever and loss of appetite.

If you have symptoms of gastroenteritis and you notice black or bloody stools, please see your doctor immediately.

4. Gastro-Intestinal Bleeding

As far as medical conditions go, this is by far the commonest cause of black stools. The bleeding can range from mild to severe, but it would always be present with other symptoms like pain, nausea, vomiting, dizziness, abdominal swelling, foul smelling poop.

When there is blood in the gut, it undergoes some chemical changes and ends up coloring the poop black. If you have a small bleed in the gut, you might just experience one episode of black poop and then it doesn’t happen again.

A larger bleed may cause persistent black poop and sometimes diarrhea with bright red blood in it. In very severe cases, it might be only blood that is passed. In such cases, an urgent visit to the emergency room is warranted so that the bleeding may be stopped.

The human gut is very extensive and a bleed anywhere from the esophagus to the intestines can cause black stools. There are specific conditions which have been known to cause black stools, the commonest ones are –

Esophageal varices – This is a condition usually seen in persons with severe liver disease. The blood vessels around the esophagus swell and eventually rupture releasing a lot of blood into the stomach and intestines. The blood becomes mixed in with poop turning it black.

Generally, those with severe liver disease and esophageal varices are closely monitored to prevent this type of bleeding. If you have liver disease and have not been evaluated for esophageal varices, please see your doctor immediately if you notice your stool has turned black.

Mallory-Weiss tear – This is a tear in the lower part of the esophagus that usually results from prolonged, violent vomiting and retching or coughing. Blood oozes from the tear into the gut and ends up in the stool.

If you have had a recent episode of violent vomiting or coughing and afterward you observed dark stools, you may need to see your doctor for further investigations.


Peptic ulcer diseaseUlcer is one of the commonest GI conditions worldwide. It involves ‘something’ (infections, medications, hormones, stress) continually stripping away the inner lining of the stomach until it eventually bleeds. There is usually associated pain in ulcer disease.

Ulcer is one of the first things that is checked for when there is a complaint of black stools and the mild causes (food and supplements) have been ruled out. It is a very common cause of black stools and if severe or left untreated, it can be fatal.

Peptic ulcer disease can be well managed and treated by your doctor. If it is caused by an infection, all you need is a course of antibiotics to eradicate the bacteria.

Gastritis – This is the inflammation of the stomach. It can be caused by an infection, auto-immune disease (the body fighting itself) or drugs like NSAIDs as mentioned before.

The inflammatory process causes the stomach to bleed, releasing blood into the stool and turning it black. This also must be managed by your doctor.

Small Intestinal Bleed – The small intestine is the part of the gut that begins right after the stomach. It averages about 20 feet in length and any affected portion can lead to black stools.

A small intestinal bleed can be due to trauma, inflammation, infection, growths, anatomical deformities and much more. Due to the variety of conditions that can occur in the small intestine alone, thorough investigations are carried out to determine the source of the bleed.

5. Gastro-Intestinal Cancer

newspaper clipping of cancer

A cancer anywhere from the esophagus to the intestines can cause a bleed in the gut. This blood turns the stool black.

A person who is older (above 50 years), has a long smoking history, has persistent black stools and unexplained weight loss may have a GI cancer and needs to consult a doctor as soon as possible.

There may be no pain or abdominal swelling. The absence of these does not rule out cancer. Conditions such as intestinal polyps and inflammatory bowel disease increase a person’s chances of developing cancer. If there is a history of these, immediate evaluation is required if black stools are observed.

How Would Black Stools Be Investigated?

Step 1 -The first step in determining the cause of any medical problem is a medical interview and a physical examination. It is during this interview that the doctor would determine if the cause may be from your diet or current medications.

Step 2 – The second step would be to run tests. Samples would be taken of your blood and your stool to check of your blood level is below normal and if your stool contains blood. The samples could also be analyzed for a lot of other things that may help with the diagnosis.

Step 3 – If blood is found in your stool and/ or your blood level is decreased you may have to have an endoscopy done. This is basically viewing your digestive tract to look for sources of bleeding.

Step X – This step isn’t numbered because a continued investigation is based on what the previous steps 1 – 3 have shown. This step includes high definition scans like CT scan or MRI scan, Tagged Red Cell scan, special blood tests, biopsies of growths.

In this step, anything can be investigated to help figure out what could be causing the bleed in your gut.

Treatment Options

Treatment is always dependent on the cause.

If the cause is food and medication, the obvious treatment option would be avoidance. When you avoid the things causing your stool to be black, you won’t have black stools anymore!

For medical conditions, treatment plans range from medication to surgery. If the bleeding is minimal, watchful waiting can be done to allow the body to stop the bleeding naturally.

GI infection

In conditions such as Inflammatory bowel disease, Peptic ulcer, and infections, prescription medication is used to stop the disease process going on leading to relief from passing black stools as well as other symptoms.

In more serious cases where the bleeding is brisk or continuous, the source of the bleed has to be identified and stopped. This can be done in the following ways

1. Endoscopy

Here, a long flexible tube with a tiny camera attached (called an endoscope) is passed through the mouth to view along the esophagus, the stomach and some parts of the small intestine. If the source of the bleed is found, using the same endoscope, it is stopped by applying heat or binding it.

2. Colonoscopy

This is essentially the same as the endoscopy except the tube goes in through the anus. The source of the bleed is searched for and when identified, it is stopped by heat or binding.

3. GI Camera

A slow bleed coming from the middle of the small intestine may be missed by both upper and lower endoscopy. In such cases, you may be asked to swallow a small pill-like camera which takes thousands of pictures of your gut and transmits them to a computer for your doctor to view.

When the location of the bleeder is seen, surgery may then be carried out in the exact location to stop the bleeding.

4. Interventional Radiology


If the bleeding is very rapid and endoscopy is not helpful, a special procedure involving a radiologist may be done. Using imaging machines, the specific artery that is bleeding is located and stopped by binding it.

5. Surgery

If all else fails, surgery is the last resort. It usually doesn’t fail because the surgeon goes into the abdomen and visually inspects the intestines to look for the problem. Once the problem is found, corrective measures are immediately done because the person is already on the operating table.


Black stools are never normal. It may be due to your diet, medications or a bleed somewhere in your digestive system.

If diet and medications are ruled out as the cause of the black stools, a visit to your physician is pertinent to determine the cause, investigate it and treat accordingly.

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Oyinkansola Kolawole, MD

Dr. Oyinkan Ogundimu is a graduate of medicine and surgery. She migrated to the United States to pursue her dream of caring for patients, her passion in life is to help people in all the ways she can including breaking down difficult to understand medical facts into simple and fun bits of information.
Oyinkansola Kolawole, MD