Black poop: what it can mean, and why you shouldn't sit on it

Short answer: black poop is sometimes just iron tablets or Pepto-Bismol, but it can also be digested blood from higher up in your gut. If there’s no clear food or medicine cause, the NHS says get urgent advice the same day. This page helps you decide fast. (Part of the poop color chart.)

What can turn poop black?

Often harmless, per MedlinePlus, Mayo Clinic and the NHS:

• iron tablets
• bismuth medicines such as Pepto-Bismol
• activated charcoal
• black licorice
• blueberries
• blood sausage

Can be serious: MedlinePlus says black or tarry stools with a foul smell most often point to bleeding in the esophagus, stomach or first part of the small intestine. The blood looks dark because it’s been digested on the way down. The doctors’ word for this is melena. MedlinePlus names peptic ulcers as the most common cause of sudden upper gut bleeding, and says blood thinners increase the risk.

How can I tell harmless black from worrying black?

You can’t be certain at home, and that’s the honest answer. This table helps you decide how fast to act, not whether to act.

What you might notice	What it can mean	What to do
Dark, formed poop the day after starting iron or taking Pepto-Bismol, feeling well	Likely the medicine	Mention it to your GP or pharmacist; get checked if unsure
Dark poop after lots of blueberries or black licorice, feeling well	Likely food	Should return to brown once the food passes; if not, get checked
Black, sticky, tar-like, foul-smelling poop	Possible upper gut bleeding (MedlinePlus)	Urgent same-day advice (NHS)
Black poop and you take blood thinners, aspirin or ibuprofen	Higher bleeding risk (MedlinePlus, NHS)	Urgent same-day advice
Black poop with tummy pain or cramps	The NHS lists stomach ulcer as a possible cause	Urgent same-day advice
Black poop plus dizziness, fainting, vomiting blood or “coffee grounds”	Possible significant bleeding (NIDDK, MedlinePlus)	Emergency: 999 or your local emergency number
Fast heart rate, pale skin, cold hands, sweating or confusion	NIDDK lists these as signs of shock	Emergency help right away

Why is black worse than red?

Not worse, just different. MedlinePlus explains that the color of blood gives a clue to where it’s from. Bright red usually comes from low down (colon, rectum or anus). Black usually comes from higher up, because it’s been digested. Upper gut bleeding can be hard to judge from the outside, which is why the NHS treats black poop as a same-day matter. See red poop for the other end.

What will the doctor ask?

MedlinePlus lists the questions you’re likely to hear. Having answers ready speeds things up:

• Do you take blood thinners such as aspirin, warfarin or clopidogrel, or an NSAID like ibuprofen or naproxen?
• Have you eaten black licorice or blueberries, or taken iron or Pepto-Bismol?
• Is every poop like this, or just one?
• Is there blood on the toilet paper only?
• Have you lost weight recently?
• When did it start?
• Any tummy pain, vomiting blood, bloating, diarrhea or fever?

Possible next steps include a stool test for blood, blood tests and an endoscopy (a camera test of the upper gut), according to MedlinePlus.

What could a useful log look like?

Mon 08:00  Meal: breakfast, first iron tablet
Tue 07:40  Poop: Type 4
Paper note: very dark, formed, not sticky, feeling fine
Paper note: called pharmacist, told to see GP if unsure
Wed 07:50  Poop: Type 4
Paper note: still dark, booked GP to confirm it's the iron

Notice what’s on paper: the color description and how you felt. PoopAI doesn’t read poop color for you, so write color down yourself and bring a photo if your doctor wants one.

Black poop myths vs facts

Myth	Fact
If it’s black, it’s definitely iron	Iron is a common cause, but MedlinePlus says black, tarry stools often mean upper gut bleeding.
Wait a few days and see	The NHS advises same-day urgent advice for black or dark red poop.
No pain means no problem	Bleeding can be painless. The NHS lists dark blood without pain as a possible medicine side effect that still needs checking.
It’s embarrassing to call	Doctors ask about poop all day. A clear description helps them help you.

How do I describe it on the phone?

Try: “My poop has been black and sticky since this morning. I take aspirin. I feel a bit lightheaded.” Color, texture, when, medicines and how you feel. That’s enough for a triage nurse to guide you. Our GP conversation guide has more.

Black poop: right now

• Any vomiting blood, fainting or heavy bleeding? Call 999 or your local emergency number
• Black and sticky, or no clear food or medicine cause? Get urgent same-day advice
• List your medicines, especially iron, bismuth, aspirin, ibuprofen and blood thinners
• Note when it started and if every poop is like this
• Don't stop prescribed medicines without asking a doctor

Where does PoopAI fit?

PoopAI can help you keep track of meals and poop shape (Bristol type 1 to 7, with optional photos) so you can show a doctor when things changed and what you ate or took. It does not check color and can’t tell you if there’s blood. That’s a job for a doctor and a lab test.

The bottom line

Black poop has harmless causes, but you can’t tell them apart from bleeding by looking. If there’s no obvious iron, bismuth or food explanation, or it’s tarry, get urgent same-day advice. If you feel faint or there’s a lot of blood, call for emergency help.

Editorial note: Written by The FixMyGut team using the NHS, NIDDK, MedlinePlus and Mayo Clinic sources listed below. It’s general information, not a diagnosis. Facts checked against those sources on November 5, 2026.