Get medical care now if your stool is black, sticky and tar-like with a strong smell, especially if you also feel dizzy, weak or faint, have belly pain, or have vomited blood or what looks like coffee grounds. This can mean bleeding in the stomach or upper gut.
Short answer
Black stool can come from iron tablets, bismuth medicines such as Pepto-Bismol, black licorice, blueberries or activated charcoal. Those are usually harmless. Black, sticky, tarry stool that smells very strong is called melena, and it usually means bleeding in the upper digestive tract. That needs prompt medical care.
What causes black stool?
Black stool is most often caused by iron supplements, bismuth medicines such as Pepto-Bismol, or dark foods, but it can also be caused by bleeding in the stomach or upper gut.
Causes that are usually harmless
- Iron supplements and vitamins that contain iron. They often give dark green or black stool.
- Bismuth medicines such as Pepto-Bismol and Kaopectate. Bismuth reacts with sulfur in your gut and turns stool black. It can also darken your tongue.
- Foods. Black licorice, blueberries, and foods with black or dark blue dye.
- Activated charcoal.
Stool darkened by these is usually dark or black but looks formed and ordinary, not shiny and sticky like tar.
Causes that need medical care
Blood from the stomach, esophagus or small intestine is digested on the way down, which turns it black and sticky. Possible causes include:
- Stomach or duodenal ulcers
- Gastritis, inflammation of the stomach lining
- Swollen veins in the esophagus (varices), often linked to liver disease
- Inflammation or tears in the esophagus
- Tumors of the stomach or upper gut
Regular use of anti-inflammatory painkillers such as ibuprofen or aspirin, blood thinners, heavy alcohol use and liver disease all raise the risk of upper gut bleeding.
How can you tell black stool from iron or Pepto-Bismol apart from bleeding?
Black stool from iron, bismuth or food usually looks formed and ordinary, while black stool from bleeding (melena) is typically sticky, tar-like and unusually foul-smelling. Only a clinician can confirm the cause.
| Food, iron or bismuth | Bleeding (melena) | |
|---|---|---|
| Texture | Usually formed, like normal stool | Sticky, tar-like, shiny |
| Smell | Usual smell | Unusually strong and foul |
| Other symptoms | None | Dizziness, weakness, pale skin, belly pain, vomiting blood |
| Timing | Starts after the food or medicine, stops a day or two after you stop | Continues with no link to food or medicine |
When should you see a doctor about black stool?
Black, sticky, tar-like stool can mean bleeding and needs medical care right away, especially with dizziness, weakness, belly pain or vomiting blood.
Usually harmless
- You take iron or Pepto-Bismol, or ate black licorice or blueberries
- The stool looks dark but otherwise normal, and you feel well
Call a doctor within a day
- Black stool with no food or medicine that explains it
- It continues more than a day or two after you stop the medicine or supplement
Get care now
- Black, sticky, tar-like stool with a strong smell
- Dizziness, fainting, a racing heart or very pale skin
- Vomiting blood or material that looks like coffee grounds
- Severe belly pain
Warning signs to know
These are signs that published medical guidance says need prompt or urgent care. The list is not complete, and ticking boxes cannot tell you whether you are ill. If you are worried, contact a clinician whatever you tick.
Questions people ask
Does Pepto-Bismol make your stool black?
Yes. Bismuth in Pepto-Bismol can turn stool black, and it can also make the tongue look dark. The effect is usually harmless and usually goes away a few days after you stop. If the stool is sticky and tar-like, do not assume it is the medicine.
Does iron make stool black?
Yes. Iron tablets commonly turn stool dark green or black. If you take iron and have no other symptoms, this is a known effect, but mention it to your doctor if you are unsure. If you also feel dizzy or have belly pain, get checked.
What does black tarry stool look like?
Black tarry stool, called melena, is sticky, shiny and very dark, like tar, with a strong foul smell. It usually indicates bleeding in the upper digestive tract and needs medical care.
What foods cause dark stool?
Black licorice, blueberries, dark chocolate cookies with black cocoa, and foods with black or dark blue coloring can darken stool. Dark stool from food looks otherwise normal.
Can black diarrhea be harmless?
It can be if it follows bismuth or iron. Black diarrhea that is sticky, smells strongly or comes with dizziness or pain should be treated as possible bleeding.
Sources
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