Black or tarry stools

A black or tarry stool can have several causes. Some medicines, supplements, and dark foods can change stool colour without causing harm. However, a truly black, sticky, tar-like stool may be melena. Melena usually means that blood has been digested while passing through the digestive tract.

The bleeding often comes from the upper digestive tract, which includes the food pipe, stomach, and first part of the small intestine. It may also come from farther down the small intestine or, less often, the right side of the colon.

Colour alone cannot confirm the cause. The stool's texture, smell, your medicines, and any other symptoms all matter.

Melena is usually jet black rather than simply dark brown. It may look shiny, feel sticky, and be difficult to flush. It often has a stronger, more unpleasant smell than usual.

You may have no pain. Depending on the cause, other symptoms can include:

• Upper abdominal discomfort, indigestion, or nausea
• Tiredness, weakness, dizziness, or shortness of breath
• Vomit containing red blood or dark material resembling coffee grounds
• A faster heartbeat or feeling faint

Iron supplements and medicines containing bismuth can also make stool black. These stools may not have the sticky, tar-like texture or distinctive smell of melena. Foods such as black liquorice, blueberries, or foods containing very dark colouring can temporarily darken stool.

Dark green stool may look black in poor lighting. Checking it under bright light can help clarify the colour, but it cannot rule out bleeding.

Medicines, supplements, and food

Iron supplements commonly darken bowel movements. Bismuth-containing medicines used for indigestion or diarrhoea can also make the stool black. Very dark foods may cause a short-lived colour change.

These causes do not usually produce other signs of blood loss. Still, do not assume a medicine or food is responsible if the stool is sticky, tar-like, or accompanied by illness.

Bleeding in the upper digestive tract

A peptic ulcer—a sore in the stomach or upper small intestine—is a common cause of upper digestive tract bleeding. Ulcers may be associated with infection by Helicobacter pylori, a type of bacterium, or with medicines such as ibuprofen, naproxen, and aspirin.

Inflammation or damage to the stomach lining can also bleed. Possible triggers include anti-inflammatory medicines, alcohol, or serious physical illness. Inflammation of the food pipe may cause bleeding as well.

Less common causes

A tear near the lower end of the food pipe can occur after forceful vomiting. Enlarged veins in the food pipe or stomach, called varices, can bleed in people with certain liver conditions. Abnormal blood vessels, growths, and cancers are other possible causes, but black stool does not mean that you have one of these conditions.

Arrange same-day medical assessment for an unexplained black, sticky, tar-like bowel movement. This is especially important if you take a blood thinner like warfarin or apixaban, have a bleeding disorder, or have a history of ulcers, digestive bleeding, or liver disease.

Seek emergency care now if black stool occurs with:

• Vomiting blood or coffee-ground-like material
• Fainting, confusion, severe weakness, or difficulty staying awake
• Marked dizziness, especially when standing
• Trouble breathing, chest pain, or a racing heartbeat
• Severe or worsening abdominal pain
• Pale, cold, or clammy skin

These symptoms can occur with significant blood loss. Do not drive yourself if you feel faint or very unwell.

If a known food, iron supplement, or bismuth medicine seems to explain the colour and you otherwise feel well, monitor the next bowel movements. Book a routine appointment if the dark colour continues after the likely cause has stopped, keeps returning, or comes with ongoing tiredness, abdominal symptoms, or unexplained weight loss.

A healthcare professional will ask when the colour change began and whether the stool is sticky or tar-like. They may ask about pain, vomiting, dizziness, alcohol use, liver problems, previous ulcers, and recent changes in bowel habits.

Bring a list of everything you take, including prescription medicines, aspirin, anti-inflammatory pain medicines, blood thinners, iron, bismuth products, and supplements. A photograph of the stool may be useful if you can take one without delaying urgent care.

Blood tests can check for anaemia, meaning too few red blood cells, and may show how much blood has been lost. Other tests can assess clotting and liver function.

If bleeding is suspected, an upper endoscopy may be needed. During this test, a thin flexible camera is passed through the mouth to examine the food pipe, stomach, and upper small intestine. It can sometimes find and treat bleeding at the same time. Other imaging or bowel tests may be used when the source remains unclear.

Treatment depends on the cause and the amount of bleeding. Significant bleeding may require monitoring in hospital, fluids through a vein, blood transfusion, or treatment during endoscopy. Treatment may also target an ulcer, inflammation, infection, abnormal blood vessel, or another underlying condition.

If iron or bismuth is responsible, the colour usually improves after the product leaves your system. Do not stop prescribed iron, aspirin, or a blood thinner without medical advice. Suddenly stopping some medicines can carry risks.

While arranging assessment, note the stool's colour and texture and any dizziness, vomiting, or pain. Avoid alcohol and non-essential anti-inflammatory pain medicines such as ibuprofen or naproxen if bleeding may be present. These steps are not a substitute for urgent evaluation of tarry stool.

Stool darkened by food or medicine often returns to its usual colour within several bowel movements after the cause is removed. The timing depends on how quickly food moves through your digestive tract.

With melena, black stools can continue for a few days after bleeding has stopped because old blood remains in the bowel. Stool colour alone therefore cannot show whether bleeding is still active.

Recovery depends on what caused the bleeding and whether it returns. Follow-up may include repeat blood tests, treatment for an ulcer or infection, medicine review, or further digestive tract testing.

Can iron make stool black?

Yes. Black stool is a common effect of oral iron. Seek advice if it is tar-like or accompanied by pain, vomiting, dizziness, faintness, or unusual weakness.

Is every black stool caused by blood?

No. Iron, bismuth, and dark foods can change stool colour. A jet-black, sticky, strong-smelling stool is more concerning for digested blood and needs prompt assessment if unexplained.

Can bleeding occur without stomach pain?

Yes. Some ulcers and other sources of digestive bleeding cause little or no pain. Lack of pain does not rule out bleeding.

What is the difference between black stool and bright red blood?

Black tarry stool often suggests blood has travelled through part of the digestive tract and been digested. Bright red blood more often comes from lower down, such as the rectum or colon, although rapid upper digestive bleeding can also appear red.