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Why does bismuth turn stool black?

Change in stool color – this is the appearance of atypical coloring of feces, which can be observed both in absolutely healthy people and against the background of various diseases. Sometimes the symptom has physiological prerequisites – eating certain foods or taking medications, but more often a change in color indicates a pathology of the digestive tract. To identify the causes of the symptom, ultrasound, endoscopic, x-ray, and laboratory research methods are used. To return the normal color of stool, medications are used to eliminate the root cause of the color change.

General characteristics

The appearance of an unusual color of stool is an objective symptom that patients always notice. The color of stool varies from grayish-white to black. In this case, the process of defecation is sometimes accompanied by pain and discomfort in the abdomen. With a visible change in the characteristics of feces, patients often experience negative psycho-emotional sensations caused by the fear of a serious illness. If the color change is physiological in nature, the person does not experience any unpleasant symptoms either during bowel movements or during the day. A change in the color of stool is often accompanied by other dyspeptic disorders: nausea, vomiting, abdominal pain, impaired stool frequency and consistency of feces, which indicates the development of diseases of the digestive tract. The combination of pale gray stool and dark urine usually indicates hepatitis and other acute inflammatory diseases of the liver. The appearance of black, brick or red feces during defecation is characteristic of bleeding from the gastrointestinal tract of varying intensity and requires an immediate visit to a gastroenterologist.

Development mechanism

Normally, stool is brown in color, which can vary from light to dark shades depending on dietary habits. This color is due to the presence of bilirubin metabolic products – stercobilin and mesobilifuscin. A change in the color of stool occurs when dyes are ingested in food or medications, or when there are pathological impurities (blood, bile pigments). With diarrhea, feces become golden yellow because their accelerated passage prevents the conversion of direct bilirubin to stercobilin. Colorless or gray stools are characteristic of the occurrence of mechanical obstructions in the paths of bile outflow into the intestines (cholelithiasis, space-occupying formations of the pancreas, duodenum), as a result of which there are no coloring substances in the stool, which are normally formed from conjugated bilirubin. The stool takes on a grayish tint and a clayey consistency when barium sulfate contrast is taken orally, due to chemical reactions in the stomach and intestines. Feces may turn greenish, which is often normal and is caused by eating a lot of fresh green vegetables. These products are rich in the pigment chlorophyll, which is not destroyed by digestive enzymes and provides a characteristic coloring. A change in the color of feces to green also occurs with pathological diarrhea, when biliverdin, a precursor of bilirubin, is massively released along with bile, which does not have time to go through all the stages of chemical transformations in the intestines. Black coloring of feces appears when taking bismuth salts, which under the influence of saliva form insoluble complexes with black sulfur. Dark coloring also occurs when iron salts enter the feces. Tarry, black stools (melena) develop when there is bleeding from the stomach and upper small intestine. The dark color is due to the conversion of hemoglobin into hematin hydrochloride under the influence of enzymes and intestinal flora. When bleeding from the colon and rectum, hemoglobin is not destroyed, so the stool is red.


  • Grayish-white stool. Grayish, “clayey” feces are often passed for several days after oral administration of barium sulfate contrast agent. Pale coloration of stool can be associated with impaired flow of bile into the duodenum due to biliary pathology, hepatitis, and pancreatic neoplasia.
  • Yellow stool. Yellow coloration is usually observed when food digestion is impaired due to enzyme deficiency. This color is characteristic of pancreatic diseases, malabsorption syndrome, and celiac disease. A golden-yellow color often indicates an excess of unchanged bilirubin.
  • Green stool. A change in color appears when there is a large amount of lettuce and green vegetables in the diet; the greenish-black color is associated with taking iron supplements. The color changes to green with diarrhea of ​​various origins and severe dysbiosis, when the rate of transit of feces through the intestines is disrupted.
  • Red stool. The appearance of a brick-red color is normally associated with excess consumption of tomatoes, red berries and vegetables. A change in the color of stool to bright red usually occurs with heavy bleeding from the lower gastrointestinal tract, which occurs with anal fissures, hemorrhoids, and ulceration of neoplasms.
  • Black feces. Stools become black when taking preparations of activated carbon and bismuth, blueberries and black currants. Black, tarry feces (melena) are a dangerous symptom that indicates profuse bleeding from the stomach and upper small intestine.

1. Gastroenterology. National Guide: brief edition / ed. Ivashkina V.T., Lapina T.L. – 2011.

2. Intestinal diseases. Clinic, diagnosis and treatment Tarasova L.V., Trukhan D.I. – 2013.

3. Outpatient examination of a proctological patient. Directory of a polyclinic doctor / Rivkin V.L. – 2009.

People don’t pay attention to the color of their stool until it is unusual, such as black. The dark color of stool can be caused by physiological and pathological reasons, which we will discuss in this article.

What gives stool its color?

Feces are human waste and undigested food particles. The normal color of stool is light to dark brown. Stool is primarily colored by bile pigments, such as stercobilin. The color of stool is affected by natural and artificial food dyes, components of medications and dietary supplements, as well as digested and undigested blood.

Minor changes in the normal color of feces should not cause concern, but why black feces in a person must be found out in order to exclude or confirm the development of various pathological processes in the body.

Foods that turn stool black

Black stools in normal health are usually the result of eating an excessive amount of foods that can change the color of feces:

  • blueberries;
  • Cherries
  • beets;
  • black licorice;
  • chokeberry;
  • black currant;
  • prunes;
  • grenade;
  • tomatoes;
  • blood sausage;
  • liver.

In this case, the stool may be dark in color the next day, but most often two days after eating a large amount of the listed products. After their cancellation, the color of the stool is restored to normal within three days.

Medicines that turn stool black

If food could not cause blackening of the stool, some medications and dietary supplements could cause it:

  • food supplements and preparations with high iron content;
  • Activated carbon;
  • anti-inflammatory drugs bismuth subsalicylate.

It should also be noted that long-term use of anticoagulants, some anti-inflammatory and analgesic drugs can cause microerosions of the gastrointestinal mucosa. Such bleeding explains why black stool, but requires consultation with a doctor, discontinuation or replacement of medications.

Pathological causes of darkening of stool

A change from normal stool color to black may be caused by red blood cells broken down by digestive enzymes. To turn the stool black, they need to remain in the intestines for a long time, which is not typical for perforation of the lower gastrointestinal tract, but is often observed with bleeding from the upper digestive tract.

The black, tarry stool is called melena. As already noted, in physiological conditions, black feces are formed, while melena has a liquid, “sticky” consistency.

Like tar, dark-colored stool is not the only symptom of internal bleeding; it is almost always accompanied by other signs of pathologies of the digestive system:

  • worsening of well-being;
  • stomach ache;
  • nausea and vomiting;
  • pressure drop;
  • weakness, dizziness;
  • pale skin.

The combination of tarry stools and the listed symptoms should be a reason to urgently seek medical help.

What diseases cause black stool?

It should be noted that melena rarely occurs in children, with the exception of newborns in the first days of life. Unlike physiological meconium, with melena in infants, black feces on the diaper are surrounded by a red rim. This is typical for necrotizing enterocolitis of newborns, which manifests itself at 1-2 weeks of life and is easily diagnosed and treated.

If tarry black feces appear in an adult, what this means should also be determined by doctors. Based on the results of blood tests, stool tests, coagulation tests and other studies, the following pathologies may be detected in the patient:

  • gastritis or stomach ulcer;
  • damage to the bulbar part of the duodenum (erosive bulbitis);
  • circulatory disorders due to intestinal ischemia;
  • stomach tumors;
  • hemophilia, thrombocytopenia and other blood clotting pathologies;
  • fibrosis, cirrhosis and other liver diseases, accompanied by increased pressure in the abdominal cavity, rupture of the vessels of the esophagus and stomach.

All these pathological conditions are accompanied by bleeding from the vessels of the digestive tract and require qualified symptomatic therapy.

black dots in stool

Sometimes people are frightened by the appearance of suspicious black inclusions in the stool: from grains to dark “worms”. Again, with normal stool color, black inclusions are nothing more than the remains of bananas, persimmons, kiwis, currant seeds, raspberries, poppy seeds and other particles of undigested food.

The pathological appearance of black dots in feces occurs with infections of the gastrointestinal tract, but in this case the color and consistency of the feces changes. They can be gray, green, yellow, discolored. The stool is foamy, loose or watery.

If a change in the color of stool causes concern in a person, if you feel well, you need to consult a therapist; if your condition worsens, you should consult a gastroenterologist or emergency care.

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