Medical Oncologist
CION Cancer Clinics
Black tarry stools: what they mean and when to go to hospital | CION Cancer Clinics
Black stools are often caused by iron tablets or dark foods. But a black, sticky, tar-like stool in someone with cirrhosis or liver cancer can mean bleeding from swollen veins in the food pipe or stomach, and that needs hospital today. This page explains how to tell the difference, the signs that mean call an ambulance now, and what doctors will do when you arrive. At CION Cancer Clinics, our team supports patients and families through symptoms, follow-up and life during and after treatment.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
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The short answer
Are black stools always a sign of bleeding?
No. Iron tablets, some stomach medicines and a few dark foods turn stools black, and none of these is dangerous. But a stool that is black, sticky like tar and has a strong, unusual smell is different. That kind of stool usually means blood has been digested on its way down from the food pipe or the stomach.
Why this matters more with liver disease
If you or your parent has cirrhosis, liver cancer or a known history of varices (swollen veins in the food pipe), tarry black stools can be the first sign of a bleed from those veins. A variceal bleed is the most dangerous emergency in liver disease. It can be slow and hidden at first, then suddenly heavy.
The rule this page is built around
Someone with liver disease who passes a black, tarry stool should go to hospital today. Not next week, not after the next clinic visit. If they also feel faint, look pale, are breathless or vomit blood, call an ambulance now. You do not need to be sure it is blood. Doctors would far rather check and find iron tablets than meet a bleed late.
Black and tarry in liver disease means hospital today, even if the person says they feel fine.What turns stool black
What else can make my stool black?
Most black stools have a harmless cause. The difference lies in how the stool looks and feels, and in who is passing it.
Iron tablets or syrup
The most common reason. Iron turns stool dark green or black, but it is usually firm and formed, not sticky, and has no unusual smell.
Many people with liver disease are given iron for a low blood count, so this overlap is common.Some stomach medicines
Medicines containing bismuth, sold for indigestion and loose motions in some countries, can turn both the tongue and the stool black. The colour fades once the medicine stops.
Dark foods
Large amounts of very dark fruit or greens, such as jamun or black grapes, can darken stool for a day. The stool looks normal otherwise.
Blood from high in the gut
Blood from the food pipe, stomach or the first part of the small bowel is digested on the way down and comes out black and tarry.
In liver disease this can come from
- Varices in the food pipe or stomach
- Irritated stomach lining from high pressure in the liver veins
- Stomach ulcers, sometimes from painkillers
- Rarely, a tumour in the stomach or bowel
Not sure whether this applies to you?
Ask an oncologist
!
Go to hospital today, or call an ambulance now
If someone with cirrhosis, liver cancer or known varices passes a black, sticky, foul-smelling stool, take them to the nearest hospital emergency department today. Call an ambulance straight away if they vomit blood or something that looks like coffee grounds, feel faint or dizzy on standing, look pale and sweaty, have a racing heartbeat, or become confused or drowsy. Do not wait to see if it happens again. Do not give food, alcohol or painkillers such as aspirin or ibuprofen on the way. Take their medicine list and latest reports with you.
At the hospital
What will the doctors do if they think it is a bleed?
Check how much blood has been lost
Pulse, blood pressure and a blood count come first. A drip is put in and fluids or a blood transfusion are given if needed. A finger test of the stool may confirm that the black colour is blood.
Start medicines for a likely variceal bleed
In someone with liver disease, doctors usually start medicines that lower the pressure in the gut veins, and antibiotics to prevent infection, before they have proof of the cause. This is standard, not a sign that things are worse than expected.
Look inside with an endoscopy
A thin camera passed through the mouth shows where the blood is coming from. If varices are bleeding, they can be tied off with small rubber bands during the same test. Read more on banding the veins.
Watch and plan prevention
Most people stay in hospital for a few days. Before going home, the team plans how to prevent a second bleed and when the next endoscopy should be.
Words you will hear
What do the hospital words mean?
- Melena
- The medical word for black, tarry stool caused by digested blood. It tells the doctor the bleeding is probably high in the gut.
- Haematemesis
- Vomiting blood. It may be bright red or dark like coffee grounds. It always needs an ambulance.
- Varices
- Swollen veins, usually in the food pipe or stomach, caused by high pressure in the liver's blood supply. They have thin walls and can burst.
- Portal hypertension
- Raised pressure in the portal vein, the large vein that carries blood from the gut to the liver. Cirrhosis and some liver tumours cause it.
- Upper GI endoscopy
- A camera test of the food pipe, stomach and first part of the bowel. It is how bleeding is found and often stopped.
- Haemoglobin
- The part of the blood that carries oxygen. A falling level tells the team how much blood has been lost.
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Commonly believed
Is it safe to wait and watch at home?
"He feels fine, so it cannot be serious."
A person can lose a lot of blood slowly before they feel weak. Feeling well does not rule out a bleed. In liver disease, black tarry stools need checking today whatever the person says.
"It is only the iron tablets."
Often it is. But iron stools are firm and do not smell unusual. If the stool is sticky, shiny or foul, or if the person is on iron and also has varices, let a doctor decide.
"We will see the oncologist at the next visit."
A suspected bleed is handled in an emergency department with endoscopy, not at a routine cancer clinic. Go there first, then tell your oncology team what happened.
"Cold milk or a home remedy will settle it."
Nothing taken by mouth stops a bleeding vein. Food and drink may also delay the endoscopy. Keep the person nil by mouth until a doctor says otherwise.
Being straight with you
What this page cannot tell you
It cannot tell you whether the stool you are looking at contains blood. Colour in a photograph or in poor light is unreliable, and even doctors confirm it with a test. If you are unsure and the person has liver disease, treat it as blood and go.
It cannot replace an emergency team
CION does not run an emergency department. For a suspected bleed, go to the nearest hospital with an emergency service and endoscopy. CION coordinates planned endoscopy and banding through accredited partner hospitals, and the oncology team will adjust cancer treatment once you are safe. Some cancer medicines, such as bevacizumab, raise bleeding risk, so tell the hospital about every medicine.
Who this does not apply to
If you have no liver disease, take iron, and pass firm, dark stools with no other symptoms, a routine visit to your doctor is reasonable. If the stools are tarry or you feel faint, go today whatever your history.
If you are a CION patient and unsure what to do, call the helpline. If there is any doubt, go to hospital first.Questions we are asked
Common questions about black stools in liver disease
How do I tell iron stools from blood?
Iron usually gives a firm, dark green or black stool with an ordinary smell. Digested blood gives a sticky, shiny, tar-like stool with a strong, unpleasant smell, sometimes loose. If the person has liver disease and you cannot tell the difference, assume it is blood and go to hospital today.
Should I stop the iron tablets?
Do not stop or start any medicine on your own. Tell the emergency doctor or your own doctor that the person takes iron, and they will decide. Bring the strip or bottle with you so they know exactly what it is and when the last dose was taken.
Can a variceal bleed stop on its own?
Sometimes the bleeding slows for a while, which is why people delay. But varices that have bled once are likely to bleed again, and the next bleed can be much heavier. That is why every suspected bleed needs a hospital assessment and a plan to prevent the next one.
Can it be a stomach ulcer instead of varices?
Yes. Ulcers are a common cause of black stools, especially in people who take painkillers like aspirin or ibuprofen. Only the endoscopy can show the real source. The treatment differs, so the doctors need to look rather than guess, even in someone known to have varices.
Does this mean the liver cancer has got worse?
Not necessarily. Varices come from the pressure in a scarred liver, and many people bleed from them whatever their cancer is doing. A tumour pressing on the portal vein can raise that pressure, so your team may review the scans once you are stable. This page cannot answer that for your case.
Should we go to a cancer hospital or the nearest hospital?
The nearest hospital with an emergency department and endoscopy. Travelling far to reach a familiar hospital loses time that matters. Carry the person's reports and medicine list, and inform the treating oncologist once they are being looked after.
Can black stools happen during cancer treatment?
Yes. Some drugs, including bevacizumab, raise the risk of bleeding in people with varices, which is why an endoscopy is often done before it is started. Read our page on bevacizumab and bleeding risk, and report any black stool to the team the same day.
What can we do at home to be ready?
Keep an up-to-date medicine list and the latest reports in one folder by the door. Agree in advance which hospital you would go to and how you would get there at night. An emergency plan on the fridge helps every family member act fast.
Your Specialists
Meet CION's liver cancer specialists. Bring your scan reports and liver blood tests.
Our medical and surgical oncologists plan liver cancer care together, weighing the tumour and how well your liver works before choosing surgery, a liver-directed procedure or medicines.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
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Sources
- MedlinePlus — Bleeding esophageal varices
- Cleveland Clinic — Esophageal Varices: Symptoms, Causes & Treatment
- Merck Manual Consumer Version — Portal Hypertension
- NHS — Cirrhosis
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Vomiting blood: call an ambulance nowThe other sign of a bleed, and the one that cannot wait at allWhat happens in hospital during a variceal bleedStep by step, from the emergency room to going homePreventing a second bleedWhat the team does so it does not happen againVarices explainedWhy these veins form and why they bleed
Talk to us
Had a bleed and unsure what happens to the cancer plan now?
Once the person is safe, our team can review the reports with you and explain how treatment may need to change. One helpline serves every CION centre.