Melena means black, tar-like poop caused by digested blood; and it can be a medical emergency. But here’s the twist: not every black stool is dangerous.
Sometimes your poop turns dark because of an iron supplement, Pepto-Bismol (bismuth subsalicylate), or even foods like black licorice and blueberries. That’s why this topic scares people: the same color can have two very different meanings.
In this guide, you’ll learn the simple clues that matter most; how it looks, how it smells, and how you feel.
You’ll also see the red flags that mean “don’t wait,” plus the common harmless reasons that usually fix themselves. If you’re unsure, this will help you choose the safest next step.
Quick answer: Is black poop dangerous?
Not always. Black stool can happen from:
- Iron supplement
- Bismuth subsalicylate (like Pepto-Bismol)
- Dark foods like black licorice, blueberries, or blood sausage
But it can be dangerous when it is melena (digested blood). Melena is often black, tarry, and foul-smelling.
Go to urgent care, ER now if you feel any of these
Seek emergency care if black stool happens with:
- Dizziness, fainting, or feeling “about to pass out”
- Weakness, shortness of breath, fast heartbeat
- Severe belly pain
- Vomit with blood or vomit that looks like coffee grounds
- Repeated black, tarry stools
These can be signs of a serious GI bleed and possible internal bleeding.
What black stool means (simple explanation)
Stool color changes for two main reasons:
1) Pigments (often harmless)
Some foods and medicines can darken stool as they pass through.
2) Digested blood (melena)
If bleeding happens in the esophagus, stomach, or first part of the small intestine, blood can turn black as it moves through your gut. That black, tarry stool is called melena.
Tip: Dark green stool can look black in low light. Check under bright light.
Melena explained (the most serious cause of black stool)
Melena is not just “dark.” It is usually:
- Jet-black
- Sticky or tarry
- Very foul-smelling
MedlinePlus notes that black or tarry stools with a foul smell often point to a problem in the upper digestive tract and most often mean bleeding.
Harmless causes of black poop (food + medicine)
Iron supplement (including prenatal vitamins)
An iron supplement can turn stool dark green or black. This is common. If you feel fine and the stool is not tarry, it is often harmless.
Bismuth subsalicylate (Pepto-Bismol)
Pepto-Bismol can make your poop look black. The NHS lists this as a common side effect and says it is harmless.
Mayo Clinic also notes bismuth subsalicylate can cause gray-black stools that go away after stopping.
Foods that can darken stool
These foods can temporarily darken stool:
- Black licorice
- Blueberries
- Blood sausage
Timing clue: If black stool starts after a new pill/medicine or a dark food biinge, and you feel okay, a harmless cause is more likely.
Dangerous causes: black stool from gastrointestinal bleeding
If black stool is tarry or you have symptoms, bleeding must be considered. Bleeding in the digestive system can be mild or life-threatening.
Common serious causes include:
Peptic ulcer
A bleeding peptic ulcer (stomach or duodenum) is a frequent source of melena. Cleveland Clinic notes melena often points to bleeding from higher up, such as a bleeding stomach ulcer.
Gastritis
Gastritis is irritation of the stomach lining. It can bleed and lead to melena.
Esophageal varices
Esophageal varices are enlarged veins in the esophagus (often linked to severe liver disease). They can bleed heavily and need emergency care.
Stomach cancer (less common, but important)
Bleeding from stomach cancer can also cause black stool. This is not the most common cause, but persistent unexplained black, tarry stools should be checked.
Black stool checklist: harmless vs melena
Use this quick guide. It is not a diagnosis, but it helps you decide what to do next.
| More likely harmless | More concerning (possible melena) |
|---|---|
| Started after iron supplement or Pepto-Bismol | No clear food/medicine cause |
| Dark stool but not sticky/tarry | Jet-black, tarry, sticky |
| No major symptoms | Dizzy, weak, short of breath, fainting |
| Improves in 1–3 days after stopping trigger | Keeps happening or gets worse |
| Normal smell | Very foul smell (common with melena) |
How Long Can Black Stool Last After Iron or Pepto-Bismol?
If your stool turns black after a new pill, the timing can help you worry less (or act faster).
- Iron supplements: Stool may stay dark as long as you take iron. It often fades after you stop, but it can take a little time for your gut to clear it.
- Pepto-Bismol (bismuth subsalicylate): Black stool is a known side effect and usually goes away within a few days after you stop.
Get medical advice sooner if:
- The stool is jet-black and sticky (tarry)
- It keeps happening with no clear trigger
- You feel weak, dizzy, short of breath, or you faint
- You vomit blood or “coffee-ground” material
When in doubt, don’t “wait it out.” It’s safer to check.
Risk Factors That Make Black Stool More Concerning
Black stool is more worrying when bleeding is more likely. You should take it extra seriously if you:
- Take blood thinners (or high-dose aspirin)
- Use NSAIDs often (ibuprofen, naproxen)
- Had a peptic ulcer or past GI bleeding
- Have liver disease (risk of esophageal varices)
- Drink heavy alcohol often
- Are older, or you already have anemia
- Have new belly pain, vomiting, or sudden weakness
Even if you feel “okay,” risk factors raise the chance that black stool is not just food or medicine.
Endoscopy vs. Colonoscopy: Which Test Checks What?
Doctors use these tests to find where bleeding may be coming from.
Endoscopy (upper endoscopy) looks at:
- The esophagus
- The stomach
- The first part of the small intestine (duodenum)
It is often used when stool looks like melena (black, tarry stool), because melena usually comes from the upper digestive tract.
Colonoscopy looks at:
- The large intestine (colon)
- The rectum
It may be used if the cause is not clear, if tests show blood loss, or if symptoms suggest a lower source.
Your doctor chooses the test based on your stool, symptoms, and risk factors.
Why is my poop black and smelly?
This is a common search for a reason.
A very foul smell + black tarry stool is a classic warning sign for melena (digested blood). MedlinePlus calls out black/tarry stools with a foul smell as a sign of upper digestive tract problems and often bleeding.
If stool is black and you feel weak, dizzy, or short of breath, treat it as urgent.
“Black stool but no pain”; can it still be serious?
Yes. Some GI bleeding happens with little or no pain. You should judge by:
- Tarry texture
- Strong odor
- Repeated black stools
- Symptoms like dizziness or weakness
What to do now (step-by-step)
Step 1: Look for a clear trigger (last 1–3 days)
- Iron supplement?
- Pepto-Bismol / bismuth subsalicylate?
- Black licorice, blueberries, blood sausage?
Step 2: Check for red flags
If stool is tarry or you feel unwell, don’t wait. GI bleeding can be serious.
Step 3: Gather quick details (helps your doctor)
Write down:
- When it started
- How many black stools you had
- Any meds/supplements (iron, bismuth, blood thinners)
- Any symptoms (dizzy, weak, short of breath)
When to see a doctor (and when it’s an emergency)
Emergency (same day / now)
- Black, tarry stool plus symptoms (dizziness, fainting, weakness, shortness of breath)
- Vomiting blood or coffee-ground vomit
- Large amount of black stool or repeated episodes
Call a doctor soon
- Black stool that keeps happening
- No clear reason (no iron, no Pepto-Bismol, no dark foods)
- Signs of anemia like tiredness, pale skin, shortness of breath
Diagnosis: what gastroenterology may do
If bleeding is possible, you may be referred to gastroenterology (digestive system care).
Common tests include:
Fecal occult blood test (FOBT)
A stool test that checks for hidden blood. It helps confirm bleeding.
Blood tests for anemia
A CBC can show low red blood cells, which may point to blood loss.
Endoscopy
An endoscopy (upper endoscopy) looks inside the esophagus, stomach, and duodenum. It can often find the bleeding source and sometimes treat it.
Colonoscopy
A colonoscopy checks the colon. It may be used when the source is unclear, when stool blood tests are positive, or when anemia needs a full workup.
Mayo Clinic notes that imaging or an endoscopic investigation can help locate the cause of GI bleeding.
FAQ:
Black stool after iron pills, should I worry?
Often no, if you feel fine. But if the stool is tarry or you have symptoms, get checked.
When to worry about black poop?
Worry more when it is jet-black, sticky, foul-smelling, keeps happening. Or comes with dizziness, weakness, fainting, shortness of breath, or vomiting blood.
Is black poop dangerous?
It can be harmless (iron, bismuth, foods). It can also be melena from bleeding, which can be serious.
How long can Pepto-Bismol make stool black?
For many people it is temporary and improves after stopping. The NHS calls it harmless.
If black stool continues or looks tarry, seek medical advice.
Can black stool happen without pain?
Yes. Upper GI bleeding can occur without strong pain.
Final takeaway (short and clear)
Black stool is often caused by iron supplement, bismuth subsalicylate (Pepto-Bismol). Or dark foods like black licorice, blueberries, and blood sausage.
But black, tarry, foul-smelling stool may be melena from gastrointestinal bleeding and can be an emergency.
Medical note: This article is for education, not a diagnosis. If you think you may have melena or feel unwell, get urgent medical care.
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Hi, I’m Evan Lexor, the voice behind Meanpedia.com. I break down English words, slang, and phrases into clear, simple meanings that actually make sense. From modern internet terms to everyday expressions, my goal is straightforward: help you understand English better, faster, and with confidence, one word at a time.
