Black, Tarry Stool: What It Means and When to Seek Urgent Care

What makes stool black and tarry — and how to tell if it's serious

When blood enters the upper digestive tract, stomach acid and digestive enzymes chemically alter it during transit, turning it from red to a dark, almost black color. The stool becomes sticky, thick, and noticeably foul-smelling — the distinctive tar-like consistency is the clinical clue 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Definition and causes of melena; upper GI bleeding sources including peptic ulcer, varices, esophagitis, Mallory-Weiss tears; role of EGD and BUN/creatinine in evaluation.

This is different from stool that is merely darker or firmer than usual. If you can press on it and it has a sticky, gummy quality, or if the smell is particularly sharp and rotten, that is much more concerning than stool that is simply a different shade. The question to ask yourself: is this sticky and tar-like, or just darker than normal?

What most commonly causes black tarry stool?

Peptic ulcer disease is the most frequent source. A sore in the lining of the stomach or duodenum (the first part of the small intestine) can bleed slowly or suddenly. Most peptic ulcers are caused by *H. pylori* bacterial infection or regular use of NSAIDs (ibuprofen, aspirin, naproxen) 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Definition and causes of melena; upper GI bleeding sources including peptic ulcer, varices, esophagitis, Mallory-Weiss tears; role of EGD and BUN/creatinine in evaluation2Ref 2Chey WD, Howden CW, Moss SF, Morgan DR, Greer KB, Grover S, Shah SC (2024).ACG Clinical Guideline: Treatment of Helicobacter pylori Infection.H. pylori as a primary cause of peptic ulcers leading to upper GI bleeding; testing and treatment recommendations.

Esophageal varices — enlarged veins in the esophagus, typically seen in people with liver disease — can bleed heavily and are a medical emergency. Esophagitis (from severe acid reflux or infections) can cause bleeding. Mallory-Weiss tears — small tears at the junction of the esophagus and stomach from forceful vomiting — are another cause 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Definition and causes of melena; upper GI bleeding sources including peptic ulcer, varices, esophagitis, Mallory-Weiss tears; role of EGD and BUN/creatinine in evaluation.

Upper GI cancers are a less common but important possibility, particularly in older adults with new symptoms and no clear alternative explanation 3Ref 3National Institute of Diabetes and Digestive and Kidney Diseases (2022).Peptic Ulcers (Stomach or Duodenal Ulcers).Peptic ulcer disease as a common cause of upper GI bleeding and black stool; cancer as a less common differential in older adults.

What can look like melena but is not bleeding?

Before alarming yourself, consider whether you have taken any of the following recently:

• Iron supplements reliably darken stool but typically leave it formed, not sticky, and without the characteristic foul odor 4Ref 4MedlinePlus / U.S. National Library of Medicine (2024).Ibuprofen: MedlinePlus Drug Information.NSAID use as a GI bleeding risk factor; iron supplements as a benign cause of dark stool.
• Bismuth-containing medications (like Pepto-Bismol) turn stool dark gray or black — and sometimes the tongue.
• Dark-colored foods — beets (which can also turn urine pink), black licorice, blueberries, activated charcoal — can temporarily darken stool.

If you recently started iron or bismuth and the stool is dark but formed and the odor is not unusual, that is a more reassuring picture. If uncertain, stop the supplement and see whether stool color normalizes within a day or two. If it doesn't, contact a clinician.

How urgently should you act?

True melena — black, sticky, foul-smelling stool — always warrants prompt evaluation, even if you feel well in the moment. Upper GI bleeding can be significant before you feel its effects 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Definition and causes of melena; upper GI bleeding sources including peptic ulcer, varices, esophagitis, Mallory-Weiss tears; role of EGD and BUN/creatinine in evaluation.

The ACG clinical guideline on upper GI bleeding emphasizes early endoscopy (esophagogastroduodenoscopy, or EGD) as both the key diagnostic and therapeutic procedure — it allows direct visualization and treatment of the bleeding source 1Ref 1Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI (2021).ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding.Definition and causes of melena; upper GI bleeding sources including peptic ulcer, varices, esophagitis, Mallory-Weiss tears; role of EGD and BUN/creatinine in evaluation. A complete blood count (CBC) and a BUN/creatinine ratio are also typically obtained, as an elevated BUN-to-creatinine ratio is a classic clue for upper GI bleeding.

If the stool looks concerning but you feel entirely well and have a clear alternative explanation (recent iron supplementation), contact your clinician the same day. Do not wait several days to see what happens.

Factors that raise the urgency

• NSAID or aspirin use: Regular use of NSAIDs is one of the most common causes of GI ulcers and bleeding. Do not stop aspirin prescribed for a cardiac condition without speaking to your clinician — but report the dark stool urgently 4Ref 4MedlinePlus / U.S. National Library of Medicine (2024).Ibuprofen: MedlinePlus Drug Information.NSAID use as a GI bleeding risk factor; iron supplements as a benign cause of dark stool.
• Liver disease or heavy alcohol use: Liver disease can cause varices that bleed severely and also impairs blood clotting. If you have known liver disease and dark stool, seek emergency evaluation.
• Blood thinners (anticoagulants): Warfarin, rivaroxaban, apixaban, and similar medications significantly increase GI bleeding risk. Dark stool in someone on anticoagulants is a higher-urgency concern.
• Age: Older adults are at higher risk for peptic ulcer disease, GI cancers, and the adverse GI effects of NSAIDs. They may also feel relatively well despite significant blood loss, making any stool color change important to evaluate.