Black stool is usually harmless when you can trace it to iron pills, Pepto-Bismol or other bismuth medicines, activated charcoal, black licorice or blueberries[1]. Black stool that is sticky, tar-like and unusually foul-smelling is different. That pattern, called melena, most often means upper gastrointestinal bleeding: blood from the esophagus, stomach or first part of the small intestine[1].
Below: how to tell stained black poop from melena, the causes of each, the medicines that raise bleeding risk, and when to get help.
Get medical help right away if black stool comes with dizziness or fainting, vomiting blood or material that looks like coffee grounds, a fast heartbeat or shortness of breath, or confusion with pale, cold, sweaty skin[2][1]. These can be signs of significant blood loss or shock and need emergency care, not home care.
Why is my poop black?
Your poop is black for one of two reasons: something you swallowed has stained it, or blood has been digested on its way through your gut[1]. Upper GI blood turns dark because it is digested in transit; fresh red blood more often comes from the colon, rectum or anus[1].
These clues help you tell the two apart:
| Clue | Usually harmless staining | Possible bleeding (melena) |
|---|---|---|
| Recent trigger | Iron, bismuth (Pepto-Bismol), activated charcoal, licorice, blueberries, blood sausage[1] | No obvious trigger; NSAIDs, aspirin or blood thinners[1] |
| Look and texture | Dark or black but formed | Black, tarry, sticky[1] |
| Smell | Ordinary | Strong, foul smell[1] |
| How you feel | Well | Dizzy, weak, tired, short of breath, or abdominal pain[2] |
| Vomit | Normal | Blood or coffee-ground material[2] |
| Stool blood test | Negative with iron and bismuth[3][4] | Positive |
Texture is not a perfect guide, so if your stool is very dark brown, almost black and you cannot link it to a food or medicine, ask a clinician. They can test the stool chemically for blood[1].
Harmless causes of black stool
Most black stool that is not tarry comes from iron, bismuth or dark foods[1]. The color should fade once the cause is gone.
| Cause | What you may notice | How long it lasts | What to do |
|---|---|---|---|
| Iron supplements | Dark or black, formed stool | While you take iron | Keep taking it as prescribed; a stool test can rule out blood[3] |
| Bismuth subsalicylate (Pepto-Bismol) | Black stool, often a black tongue first | Several days after the last dose[4][5] | Nothing, if you feel well |
| Activated charcoal | Black stool | Until it passes | Nothing, if you feel well[1] |
| Black licorice, blueberries, blood sausage | Dark to black stool | Until the food has passed | Note what you ate[1] |
Does iron make your poop black?
Yes. Iron pills are a standard cause of black stool[1]. The color does not mean iron is causing bleeding: in a study of 25 healthy volunteers taking 900 mg of ferrous sulfate a day, every guaiac stool blood test stayed negative, and a quantitative test showed no extra blood loss[3]. Tarry, sticky or foul-smelling stool while you take iron still needs a check, because that is the pattern of melena[1].
Black stool after Pepto-Bismol
Bismuth subsalicylate, the active ingredient in Pepto-Bismol, can cause a temporary, harmless darkening of the tongue and black stool[4]. The manufacturer explains that bismuth reacts with sulfur in the mouth and gut to form black bismuth sulfide, which is why the tongue often darkens first[5]. The color usually clears within several days of the last dose[4], sometimes longer in older adults, whose gut transit is slower[5].
The prescribing label for a bismuth-containing treatment states that this darkening "should not be confused with melena" and that it does not interfere with standard occult blood tests[4].
Foods, blood-based dishes and activated charcoal
Black licorice, blueberries and blood sausage can all darken stool[1]. Dishes made with animal blood can mimic melena closely: one emergency department report describes a 3-year-old with "black, sticky" stool, which turned out to follow two bowls of pork blood soup[6]. If you are unsure, write down what you ate in the last 48 hours before you call.
What does melena stool look like?
Melena is the medical term for black, tarry stool with a foul smell, caused by digested blood[1]. It is a strong signal of an upper GI source. In a JAMA systematic review, a patient-reported history of melena raised the likelihood of upper GI bleeding about fivefold (likelihood ratio 5.1-5.9), and melena seen on examination raised it 25-fold[7]. Blood clots in the stool made an upper source much less likely[7].
Two exceptions are worth knowing:
- Very fast upper bleeding can come out red rather than black, because the blood has less time to be digested[8].
- Melena can come from lower down. When an upper endoscopy finds nothing, colonoscopy finds a likely source in about 4.8% of people with melena, more often a colon tumor than in screening patients[9].
Melena vs. hematochezia
| Melena | Hematochezia | |
|---|---|---|
| Color | Black, tarry | Bright or dark red blood |
| Usual source | Esophagus, stomach, duodenum[1] | Colon, rectum, anus[1] |
| Exception | Slow bleeding from the lower gut[9] | Brisk upper bleeding[8] |
Color is not part of stool form scoring, so record it separately from your type on the Bristol stool chart.
What causes black, tarry stool?
Peptic ulcers are the most common cause of acute upper GI bleeding[1]. Upper GI bleeding affects roughly 48 to 160 people per 100,000 each year and accounts for about 300,000 US hospital stays annually[10].
| Cause | What it is | Clues |
|---|---|---|
| Peptic ulcer | A sore in the stomach or duodenum lining | NSAID use or H. pylori infection[2] |
| Gastritis | Inflamed or damaged stomach lining | H. pylori, NSAIDs, blood thinners, alcohol[2] |
| Esophagitis | Inflamed esophagus that can ulcerate | Often from acid reflux (GERD)[2] |
| Varices | Widened veins in the esophagus or stomach that can burst | Most often linked to liver cirrhosis[2][1] |
| Mallory-Weiss tear | A tear in the lower esophagus | Follows severe or violent vomiting[2] |
| Tumors | Benign growths or cancer of the esophagus, stomach, duodenum or ampulla of Vater | Weight loss, ongoing symptoms[1] |
| Small bowel bleeding | Abnormal vessels, inflammation such as Crohn's disease, polyps[2] | May need capsule endoscopy or enteroscopy to find[1] |
If you have had an ulcer before, our pages on H. pylori gastritis and peptic ulcers cover causes and treatment in depth.
Who is at higher risk of bleeding?
Some medicines and histories make a bleeding cause more likely. In a review in American Family Physician, the strongest risk factors for upper GI bleeding were[10]:
- a previous upper GI bleed (relative risk 13.5);
- taking an anticoagulant (relative risk 12.7);
- high-dose NSAID use (relative risk 5.8);
- older age (relative risk 5.6).
In randomized trials of high-dose NSAIDs, upper GI complications such as bleeding rose about fourfold with ibuprofen and naproxen and almost twofold with coxibs and diclofenac[11]. Aspirin raises GI bleeding risk by 37%, and SSRI antidepressants by 55%, more when combined with NSAIDs[10]. Corticosteroids are linked to about 40% more GI bleeding or perforation, mainly in hospitalized patients[12].
If you take any of these medicines, do not stop them on your own. Tell your prescriber about black stool the same day.
Why does black poop come and go?
Black stool that comes and goes has a harmless explanation if it tracks your iron doses, a few doses of bismuth, or a meal. It can also signal slow, ongoing bleeding. Chronic GI bleeding often causes mild symptoms that come and go, with stool that is sometimes black and tarry and sometimes mixed with red blood[2]. Over time it can cause anemia, with tiredness, pale skin and shortness of breath[2].
If black stool keeps returning without iron, bismuth or a dark food to explain it, book an appointment even if you feel well.
Where do gut microbes fit in?
Gut bacteria play a part in both sides of this symptom.
- Ulcers. NSAIDs and Helicobacter pylori infection together account for about 80% of peptic ulcer disease and ulcer bleeding[10]. Testing for and treating H. pylori is part of standard care after an ulcer bleed[10].
- Bismuth staining. Gut bacteria make hydrogen sulfide, and bismuth binds it. In a lab study, the sulfate-reducing bacterium Desulfovibrio desulfuricans precipitated bismuth as bismuth sulfide nanocrystals[13]. This is a test-tube finding, but it matches how bismuth's black color forms.
- Blood pigments. Gut bacteria also process bilirubin, a by-product of broken-down haem. In 2024, researchers identified BilR, the bacterial enzyme that turns bilirubin into urobilinogen; it is nearly universal in healthy adults but less common in newborns and in people with inflammatory bowel disease[14].
No probiotic or diet changes whether black stool is from bleeding. That needs a clinical assessment.
What will a doctor check?
A clinician first decides how urgent the situation is, then looks for the source. Expect questions about blood thinners, NSAIDs, iron, bismuth, licorice or blueberries, how many episodes you have had, weight loss and other symptoms[1].
Common next steps include[1]:
- Blood tests: a complete blood count, chemistry and clotting tests.
- A stool test for blood.
- Upper endoscopy (EGD) to look at the esophagus, stomach and duodenum, often with H. pylori testing.
- Colonoscopy, capsule endoscopy or CT angiography if the upper scope is normal.
Emergency teams often use the Glasgow-Blatchford score, built from simple clinical and lab measures. The American College of Gastroenterology suggests that very-low-risk patients (score 0-1) may go home with outpatient follow-up, and that people admitted with upper GI bleeding have endoscopy within 24 hours[15]. In a UK study of 676 patients, 68% of those classed as low risk were managed as outpatients without adverse events[16]. Upper GI bleeding remains a common emergency with a reported mortality of 2-10%, which is why tarry stool is never a wait-and-see symptom[17].
When to see a doctor
Go to the emergency department or call emergency services if you have black stool with:
- dizziness, lightheadedness or fainting[1];
- vomiting blood or coffee-ground material[2];
- a fast heartbeat, shortness of breath, confusion, or pale, cold, sweaty skin[2].
Contact a clinician the same day if:
- your stool is black, tarry, sticky or foul-smelling, even if you feel well[1];
- you take blood thinners, aspirin, NSAIDs or steroids, or have liver disease or a past ulcer[10].
Book a routine appointment if:
- black stool keeps coming back without iron, bismuth or food to explain it[2];
- you also have tiredness, pale skin or unexplained weight loss[2][1].
People whose melena has no upper source have a higher rate of colon tumors, so a recommended colonoscopy is worth completing[9]. For more on the condition itself, see our page on colorectal cancer.
This article is for general educational purposes and is not medical advice. Black, tarry stool can signal internal bleeding, and only a clinical assessment and testing can find the cause. Talk to a qualified healthcare professional before stopping or changing any medicine, and seek care promptly, particularly if you are pregnant, immunocompromised, taking blood thinners or other prescription medication, or managing a diagnosed condition.
Frequently Asked Questions
Does black poop mean liver problems?
Not usually, but it can. Liver cirrhosis can cause varices, which are widened, overgrown veins in the esophagus and stomach that can burst and bleed. That blood is digested on its way down and can come out as black, tarry stool. If you have known liver disease, heavy alcohol use or hepatitis and notice tarry stool, get medical care the same day. Black stool after iron, Pepto-Bismol or blueberries has nothing to do with the liver.
Can prednisone cause black stool?
Prednisone does not stain stool black, but corticosteroids are linked to a higher risk of stomach and intestinal bleeding, and that bleeding can show up as black, tarry stool. A 2014 meta-analysis of 159 placebo-controlled trials (33,253 people) found corticosteroids raised the risk of GI bleeding or perforation by about 40%. The increase was significant in hospitalized patients; in outpatients, bleeding was rare (0.13%). Do not stop a prescribed steroid on your own; call your prescriber if your stool turns black.
What cancers cause black tarry stools?
Cancers of the esophagus, stomach, duodenum and ampulla of Vater can bleed and cause black, tarry stool, and small-bowel tumors can too. Less often, melena comes from the colon: when an upper endoscopy is normal, people with melena are more likely than screening patients to have a colon tumor. Cancer is one cause among many; peptic ulcers are the most common cause of upper GI bleeding. Only an examination, usually endoscopy, can find the source.
Should I go to the ER for black stool?
Go to an emergency department if black stool comes with dizziness or fainting, vomiting blood or coffee-ground material, a racing heart, shortness of breath, confusion, or pale, cold, sweaty skin. These can signal significant blood loss or shock. If the stool is tarry but you feel well, contact a clinician the same day. If you recently took iron or bismuth and the stool is formed and not sticky, it is usually safe to wait and watch for a few days.
Is black diarrhea serious?
It can be. Black, foul-smelling stool can signal upper GI bleeding whether it is formed or loose, so it needs prompt assessment, especially with weakness or dizziness. Bismuth subsalicylate, often taken for diarrhea, also turns stool black, and that darkening is harmless and fades within several days. If you cannot link black diarrhea to bismuth or iron, treat it as possible bleeding. For other causes of loose stool, see our guide to diarrhea.
What can be mistaken for blood in poo?
Several foods and medicines. Iron supplements, bismuth subsalicylate (Pepto-Bismol), activated charcoal, black licorice, blueberries and blood sausage can turn stool black, and beets or foods with red coloring can make it look reddish. A clinician can tell them apart with a chemical stool test for blood. Oral iron did not trigger a positive guaiac test in a study of 25 volunteers, and bismuth's darkening does not interfere with standard occult blood tests, according to its prescribing label.
What could be causing black stool and shortness of breath?
Black stool with shortness of breath can mean you are losing blood. Acute gastrointestinal bleeding can cause black or tarry stool along with shortness of breath, dizziness, fainting and tiredness, and slower bleeding can lead to anemia, which also causes breathlessness and pale skin. This combination needs urgent medical care, especially if you also feel faint, have a racing heart or vomit blood or coffee-ground material.
What is the unhealthiest poop color?
The colors most linked to bleeding are black and red. Black, tarry, foul-smelling stool usually points to bleeding in the esophagus, stomach or duodenum, and red or fresh blood most often comes from the colon, rectum or anus. Both need a clinician's opinion unless a food or medicine clearly explains them. For what other colors and shapes mean, see our Bristol stool chart guide.
References
- MedlinePlus Medical Encyclopedia. Black or tarry stools. U.S. National Library of Medicine. 2026. Available at: https://medlineplus.gov/ency/article/003130.htm ↩
- National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & Causes of GI Bleeding. NIDDK, National Institutes of Health. 2024. Available at: https://www.niddk.nih.gov/health-information/digestive-diseases/gastrointestinal-bleeding/symptoms-causes ↩
- McDonnell WM, Ryan JA, Seeger DM, Elta GH. Effect of iron on the guaiac reaction. Gastroenterology. 1989;96(1):74-78. doi:10.1016/0016-5085(89)90766-x ↩
- U.S. National Library of Medicine, DailyMed. Bismuth Subsalicylate Chewable Tablets/Metronidazole Tablets/Tetracycline Hydrochloride Capsules: prescribing information. DailyMed. 2019. Available at: https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=0c809fa5-c630-4bf1-a0fc-5ee875008807&type=display ↩
- Pepto Bismol. Why Are My Poop and Tongue Black After Taking Pepto Bismol?. Pepto Bismol (manufacturer FAQ). 2026. Available at: https://pepto-bismol.com/en-us/faq/black-stool-black-tongue ↩
- Alder MN, Timm NL. A "Rare" Case of Melena in a 3-Year-Old. Pediatric Emergency Care. 2011;27(11):1084. doi:10.1097/PEC.0b013e31823606b5 ↩
- Srygley FD, Gerardo CJ, Tran T, Fisher DA. Does This Patient Have a Severe Upper Gastrointestinal Bleed?. JAMA. 2012;307(10):1072-1079. doi:10.1001/jama.2012.253 ↩
- Kamboj AK, Hoversten P, Leggett CL. Upper Gastrointestinal Bleeding: Etiologies and Management. Mayo Clinic Proceedings. 2019;94(4):697-703. doi:10.1016/j.mayocp.2019.01.022 ↩
- Etzel JP, Williams JL, Jiang Z, Lieberman DA, Knigge K, Faigel DO. Diagnostic yield of colonoscopy to evaluate melena after a nondiagnostic EGD. Gastrointestinal Endoscopy. 2012;75(4):819-826. doi:10.1016/j.gie.2011.11.041 ↩
- Wilkins T, Wheeler B, Carpenter M. Upper Gastrointestinal Bleeding in Adults: Evaluation and Management. American Family Physician. 2020;101(5):294-300. Available at: https://www.aafp.org/pubs/afp/issues/2020/0301/p294.html ↩
- Coxib and traditional NSAID Trialists' (CNT) Collaboration; Bhala N, Emberson J, Merhi A, et al.. Vascular and upper gastrointestinal effects of non-steroidal anti-inflammatory drugs: meta-analyses of individual participant data from randomised trials. Lancet. 2013;382(9894):769-779. doi:10.1016/S0140-6736(13)60900-9 ↩
- Narum S, Westergren T, Klemp M. Corticosteroids and risk of gastrointestinal bleeding: a systematic review and meta-analysis. BMJ Open. 2014;4(5):e004587. doi:10.1136/bmjopen-2013-004587 ↩
- Barton LL, Granat AS, Lee S, et al.. Bismuth(III) interactions with Desulfovibrio desulfuricans: inhibition of cell energetics and nanocrystal formation of Bi2S3 and Bi0. BioMetals. 2019;32(5):803-811. doi:10.1007/s10534-019-00213-4 ↩
- Hall B, Levy S, Dufault-Thompson K, et al.. BilR is a gut microbial enzyme that reduces bilirubin to urobilinogen. Nature Microbiology. 2024;9(1):173-184. doi:10.1038/s41564-023-01549-x ↩
- Laine L, Barkun AN, Saltzman JR, Martel M, Leontiadis GI. ACG Clinical Guideline: Upper Gastrointestinal and Ulcer Bleeding. American Journal of Gastroenterology. 2021;116(5):899-917. doi:10.14309/ajg.0000000000001245 ↩
- Stanley AJ, Ashley D, Dalton HR, et al.. Outpatient management of patients with low-risk upper-gastrointestinal haemorrhage: multicentre validation and prospective evaluation. Lancet. 2009;373(9657):42-47. doi:10.1016/S0140-6736(08)61769-9 ↩
- Stanley AJ, Laine L. Management of acute upper gastrointestinal bleeding. BMJ. 2019;364:l536. doi:10.1136/bmj.l536 ↩