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Did you take Pepto-Bismol, Kaopectate, or another bismuth product in the last few days? Bismuth turns stool black, and often the tongue too.
Are you taking an iron supplement? Iron commonly darkens stool anywhere from dark green to near-black.
Did you eat a lot of something very dark? Black licorice, blueberries, blood sausage, or activated charcoal are the established culprits.
Is the stool sticky and tarry, and does it smell distinctly, memorably bad?
If one of the first three is yes and the stool otherwise looks and feels normal for you, you have a plausible explanation. That's genuinely reassuring, but it isn't the same as ruling bleeding out. You should still call your doctor. If you have no explanation at all, or the stool is tarry, call your doctor.
And if you're also vomiting blood or something that looks like coffee grounds, feeling dizzy or faint, unusually weak, or short of breath, stop reading and go to an emergency room.
What melena looks like, and what it can't tell you
Doctors have a specific word for black stool caused by bleeding: melena. Black stool from Pepto or iron isn't melena, it's stained stool.
Classic melena is jet black with a sticky, tarry consistency, often compared to roofing tar. Stained stool tends to keep whatever texture your stool normally has. Melena also has a particularly strong, offensive odor, a byproduct of blood being broken down as it travels.
Some causes of upper GI bleeding also cause diarrhea, which makes melena wetter than the textbook description. And a small amount of bleeding may look more dark brown than truly black.
So the tarry-and-foul description is a signal that should raise your suspicion, not a test you can fail your way out of. Stool that doesn't match it hasn't excluded anything.
One nuance that spares unnecessary panic: after a bleed, stools can stay dark for several days. Black stool today doesn't necessarily mean active bleeding today. It does mean the cause needs explaining.
Medications and supplements that stain stool black
Bismuth subsalicylate. The active ingredient in Pepto-Bismol, Kaopectate, and store-brand equivalents. In the gut, bismuth reacts with sulfur compounds to form an insoluble black salt that passes through. The same reaction can darken the tongue, which is a useful confirmation when you see both. Color should return to normal within a few days of your last dose.
Iron supplements. Most of an oral iron dose isn't absorbed, and what's left darkens stool. Black or dark green color by itself is expected. Tarry-looking black stool is a different matter, and it still warrants contacting your doctor even if you take iron. The color effect appears dose-dependent: in a study of low-dose iron in pregnancy, black stools were reported by 31% of women on ferrous sulphate at 50 mg of iron, versus 8% on ferrous bisglycinate at 25 mg. That's a specific population, so read it as a direction rather than your odds.
Activated charcoal. Sold as a supplement and used clinically for some poisonings. Same logic as anything else black you swallow.
One caveat applies to all three. These explain black stool. They don't rule out bleeding happening at the same time. If your stool turns tarry, starts smelling foul, or doesn't return to normal within several days of stopping, the supplement is no longer a sufficient explanation.
Foods that do it
The well-established ones are black licorice, blueberries in quantity, and blood sausage or black pudding. MedlinePlus lists exactly these alongside iron, charcoal, and bismuth.
Food-related color changes resolve once the food has passed through.
Beets and red-colored foods make stool look reddish rather than black, which sets off a different alarm with a similarly benign explanation.
What causes actual bleeding
Melena usually points to bleeding in the upper GI tract: the esophagus, stomach, or duodenum. Less commonly, bleeding farther down can also turn black if it stays in the intestine long enough. The reverse happens too, since a fast upper GI bleed can come out red.
Peptic ulcers are the most common cause of acute upper GI bleeding. Ulcers develop when stomach acid damages the lining, usually because of H. pylori infection or regular NSAID use.
Other causes include gastritis, inflammation or erosion of the stomach lining, a tear in the esophagus from forceful vomiting, enlarged veins in the esophagus or stomach that can bleed, and cancers of the esophagus or stomach.
Two risk factors are common and easy to forget you have:
Blood thinners and antiplatelet medication. Warfarin, apixaban, rivaroxaban, clopidogrel, and daily aspirin all raise bleeding risk and make black stool more urgent to report.
Regular NSAID use. Ibuprofen and naproxen taken frequently, especially at higher doses, are a well-established cause of stomach lining damage.
Heavy alcohol use contributes too, both to gastritis and to the liver changes behind bleeding varices. We've written separately about what alcohol does on its way through.
Variations people ask about
Black and watery. Melena isn't always tarry. When diarrhea is also present, bleeding can produce wetter black stool, which makes texture less useful as a clue and is a reason to lower your threshold for calling.
Black specks rather than solid black. These can be food particles: blueberry skins, poppy seeds, and pepper flakes all show up as flecks, the same way other recognizable food does. If specks persist without an explanation, they're worth mentioning.
Very dark brown, almost black. This can still fall within normal stool color variation. True jet-black or tarry stool is a different thing.
Dark green, almost black. Often bile that moved through quickly, or iron, or dark greens. Our piece on green stool and stomach pain covers that end.
When to call, and when to go now
Go to an emergency room if black stool comes with:
- Vomiting blood, or vomit that looks like coffee grounds
- Dizziness, lightheadedness, or fainting
- Racing heart or shortness of breath
- Confusion, or feeling cold and clammy
- Severe weakness
Get medical advice the same day if:
- The stool is black and you have no explanation for it
- It's tarry, sticky, or smells distinctly foul
- It's happened more than once
- You take blood thinners, antiplatelet drugs, or NSAIDs regularly
- You also have stomach pain, heartburn, unexplained weight loss, or loss of appetite
- You took bismuth or iron, stopped, and the color hasn't normalized after several days
Reasonable to watch if:
- You can point to a bismuth product, iron supplement, or dark food
- Texture and smell are normal for you
- You feel well
- It resolves as expected
Even then, mentioning it at your next appointment costs nothing. MedlinePlus advises contacting a provider for any change in stool color, and clinicians would rather hear about it.
What a doctor may do
Your doctor visit will likely be a lot more ordinary than you expect.
History and exam first. Expect specific questions: what did it look like, what did it smell like, when did it start, was it one stool or every stool since, have you taken bismuth or iron or eaten anything dark, are you on blood thinners or NSAIDs, any abdominal pain, any vomiting, any weight loss. They'll examine your abdomen, and possibly do a brief rectal exam.
Most people can't answer the "was it every stool or just one" question with any confidence, which is a shame, because it's one of the more useful things to bring in. That's part of why we built Throne the way we did: it keeps a quiet record of what happens in the toilet without asking you to log anything, so the answer already exists when someone asks. It doesn't diagnose anything, and it can't tell blood from bismuth. It just means you aren't reconstructing last Tuesday from memory. If you'd rather do it manually, we've written a guide on what to record.
Bloodwork. A complete blood count can show whether you're anemic and help gauge the severity of bleeding. With a very recent bleed, though, blood counts don't always reflect the full loss immediately.
A stool test. Your provider can test stool chemically for blood you can't see, which helps sort stained stool from melena.
Upper endoscopy, if bleeding is suspected. Also called an EGD. You'll be sedated, and a thin flexible camera goes through your mouth into the esophagus, stomach, and top of the small intestine. It typically takes 10 to 20 minutes and most people remember little of it.
This is the key test for suspected upper GI bleeding, and the reason is worth knowing: it isn't only a look. If there's an active bleed, the bleeding can often be treated during the same procedure, with a clip, a band, cautery, or an injection.
If an ulcer or inflammation turns out to be the cause, treatment usually involves acid-suppressing medication, plus antibiotics if H. pylori is present.
What to bring
- When you first noticed it
- Whether it's been every stool since, or just one or two
- Texture and smell, in your own words
- Everything you've taken in the past week, including over-the-counter medicine and supplements
- Any other symptoms, even ones that seem unrelated
Common questions
Q: How long does black poop last after Pepto-Bismol?
Usually a few days after your last dose. Beyond that, it needs a second explanation.
Q: Does black poop always mean bleeding?
No. Bismuth, iron, activated charcoal, and dark foods all stain stool black with no blood involved. But black stool that's tarry, foul-smelling, or unexplained should be evaluated.
Q: Is black poop an emergency?
Not necessarily. A known cause like bismuth or iron may explain it. But unexplained black or tarry stool warrants prompt medical advice, and black stool with vomiting blood, dizziness, weakness, or shortness of breath warrants emergency care.
Q: What if my poop is black but I feel completely fine?
Bleeding from an ulcer can be painless, so feeling well doesn't rule it out. Without a dietary or medication explanation, it's still worth a call.
Q: Can stress cause black poop?
Not directly. Stress affects motility and can change frequency and consistency, which we cover in our piece on anxiety and bowel changes, but it doesn't turn stool black.
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