Black stool is most often caused either by something harmless you ate or took (like iron or bismuth meds) or by bleeding higher up in your digestive tract, which is more serious and needs urgent care if accompanied by other symptoms. If your stool is truly black, shiny, and tar-like (melena), especially with symptoms like weakness, dizziness, stomach pain, or vomiting blood, emergency medical evaluation is recommended.

Quick Scoop: Why stool turns black

  • Dark foods and supplements can stain stool without being dangerous, including iron tablets, bismuth-containing medicines (e.g., some diarrhea/heartburn remedies), black licorice, blueberries, dark chocolate, and blood sausage. Color usually goes back to normal within a few days of stopping them.
  • Internal bleeding in the upper gut (esophagus, stomach, or upper small intestine) can make stool look black and tarry because blood is digested as it moves through, changing from red to very dark. This is a medical red flag rather than a cosmetic color change.

Common harmless causes

  • Foods : Black licorice, blueberries, dark chocolate, iron-rich meats, and some heavily pigmented or dyed foods can darken stool temporarily. This usually happens without pain or other symptoms and resolves once your diet changes back.
  • Supplements and medicines :
    • Iron supplements frequently cause dark green to black stool and mild constipation.
* Bismuth subsalicylate (in some overā€‘theā€‘counter stomach/diarrhea medicines) reacts with sulfur in your gut and forms black bismuth sulfide, which colors your stool.

* Activated charcoal products, including ā€œdetoxā€ supplements, can also make stool appear jet black.

Serious medical causes

  • Bleeding ulcers or gastritis : Ulcers or inflamed stomach/duodenal lining can bleed slowly, with the digested blood turning stool black and tarry, often with upper abdominal pain, nausea, or anemia symptoms like fatigue.
  • Esophageal or stomach vein problems : Swollen veins (varices) from liver disease can bleed and cause black stool, sometimes with vomiting blood, dizziness, or fainting.
  • Tumors and cancers : Cancers of the esophagus, stomach, or upper small intestine may bleed intermittently, leading to recurrent black stools plus signs such as weight loss, fatigue, or appetite changes.
  • Medicationā€‘related damage : Heavy or long-term use of NSAIDs (like ibuprofen or aspirin) and some other drugs can erode the stomach lining and cause bleeding, showing up as black stool.

When to watch vs. when to worry

  • More reassuring if:
    • You recently started iron, bismuth meds, charcoal, or ate a lot of dark foods, and you feel otherwise well.
* The color fades back to brown within a few days after stopping the likely trigger.
  • Get sameā€‘day urgent medical care (ER or emergency clinic) if:
    • Stool is black, tar-like, and foul-smelling, especially if you did not recently take iron, bismuth, or charcoal.
* You have any of these: dizziness, fainting, racing heartbeat, shortness of breath, vomiting blood or coffeeā€‘ground material, severe or worsening abdominal pain, or are on blood thinners.

Practical next steps

  • Think back over the last 3ā€“5 days: new meds, vitamins, supplements, or dark foods are important clues.
  • If you can clearly link the color to something you ate or took, stop it if safe and watch for 24ā€“48 hours; if the stool stays black or you feel unwell at any point, see a doctor promptly.
  • If you are pregnant, elderly, have liver disease, heart disease, or take blood thinners, err on the side of immediate medical evaluation for any new black, tarry stool.

Information gathered from public forums or data available on the internet and portrayed here.