Blood in stool is one of the most alarming things a person can notice. It can show up as bright red blood, or it may turn your stool dark and tar-like. Either way, it is never something to ignore. This article explains what causes digestive bleeding, what signs to watch for, and when you need to see a doctor.
What Does Blood in Stool Look Like?
Digestive bleeding does not always look the same. The appearance depends on where the bleeding is happening in your digestive tract.
Bright red blood in stool usually comes from the lower part of your digestive tract — such as the rectum or colon. Dark, tar-like, black stool (called melena) points to bleeding higher up, like in the stomach or small intestine.
Sometimes, vomiting also occurs alongside digestive bleeding. If vomit looks like dark coffee grounds, that is a sign of blood that has been partially digested. This is called hematemesis, and it requires urgent medical attention.
Many people feel well enough that they delay seeing a doctor. However, the symptoms may ease on their own for a short time — and this can give a false sense of recovery. The underlying cause is often still there and needs treatment.
Common Causes of Blood in Stool
Digestive bleeding is not a disease on its own. It is a complication of an existing condition that has worn away part of the digestive tract wall, often damaging a blood vessel. There are many possible causes, but some are far more common than others.
Upper Digestive Tract Bleeding
More than 95% of upper digestive bleeds come from four main conditions. These are peptic ulcers, stomach cancer (gastric cancer), gastritis caused by medications or irritants, and advanced liver cirrhosis.
Upper digestive bleeding tends to produce dark or black stool rather than bright red blood. It may also cause vomiting of blood or coffee-ground material. These are serious symptoms that need prompt assessment.
Lower Digestive Tract Bleeding
The most common cause of bright red blood in stool is hemorrhoids — swollen veins around the rectum or anus. Hemorrhoids are very common and are usually not dangerous. However, they can be uncomfortable and may need treatment.
It is important to note that colorectal cancer must always be ruled out when rectal bleeding occurs. Cancer that begins in the colon is called colon cancer. Cancer that begins in the rectum is called rectal cancer. Both can cause bleeding that looks similar to hemorrhoid bleeding. For more information, visit Health Canada’s digestive health resources.
In addition, some bleeds do not have a single clear source. These are called diffuse bleeds, and they require more detailed investigation to identify.
Medications That Can Cause Digestive Bleeding
Some digestive bleeds are not caused by a pre-existing digestive disease. Instead, they result from medications that irritate or weaken the stomach lining. This is an important and often overlooked cause.
A bleed may be medication-related if it follows a week or more of taking certain drugs. Common culprits include:
ASA (Aspirin) — widely used for heart health
NSAIDs — such as ibuprofen (Advil), naproxen (Aleve), diclofenac, and indomethacin
Blood thinners (anticoagulants) — such as warfarin or newer anticoagulants
Antiplatelet drugs — such as clopidogrel (Plavix)
Corticosteroids — such as prednisone or dexamethasone
Some antibiotics used to treat tuberculosis
If you have a peptic ulcer and regularly take any of these medications, your risk of serious digestive bleeding is significantly higher. Always let your family doctor or pharmacist know about all medications you take — including over-the-counter drugs. Learn more about medication-related gastrointestinal bleeding at Mayo Clinic.
Warning Signs of Digestive Bleeding
The signs of digestive bleeding range from very mild to life-threatening. How serious the symptoms are depends on how much blood has been lost, how fast it happened, and what caused the bleed.
Signs of a Minor Bleed
A person with a small digestive bleed often feels relatively well. They may visit a walk-in clinic mainly because they are frightened by seeing blood. Their blood pressure is usually normal, and their body has compensated for the small blood loss on its own.
However, even a minor bleed deserves medical attention. It could be a warning sign of a more serious condition developing underneath.
Signs of a Serious Bleed
A major digestive bleed can be a medical emergency. Signs include:
Feeling too dizzy or weak to stand, especially when moving from lying down to standing up
Pale or cold, clammy skin
Rapid, weak pulse
Low blood pressure — for example, a drop to 100 mmHg or below in someone who was previously normal or even high
Extreme thirst
Ringing in the ears
Blurred vision
Cold sweats
These symptoms can appear when someone loses one litre of blood or more in a short period of time. A simple blood test — checking haemoglobin and haematocrit levels — can confirm significant blood loss. If you or someone near you shows these signs, call 911 or go to the nearest emergency room immediately.
Gradual Bleeding Over Weeks or Months
Sometimes, a bleed develops slowly over weeks or even months. In these cases, the body partly adapts to the gradual blood loss. As a result, symptoms may be less obvious — mainly fatigue and mild weakness from anaemia (low iron in the blood).
However, people with serious heart or cardiovascular conditions handle anaemia much more poorly. For them, even gradual bleeding is dangerous and needs fast treatment.
Research also shows that most digestive bleeds happen more often in spring and autumn. This may be linked to seasonal flare-ups of peptic ulcer disease. People between the ages of 50 and 70 are most commonly affected.
When to See a Doctor
Any time you notice blood in stool — whether bright red or dark black — you should speak with a healthcare provider. Do not wait to see if it goes away on its own.
For mild symptoms with no dizziness or pain, start by booking an appointment with your family doctor. If you do not have a family doctor, most provinces have walk-in clinics that can do an initial assessment. Some provinces also offer nurse practitioner-led clinics as part of their provincial health plan.
If you experience severe symptoms — such as dizziness, fainting, rapid heartbeat, or very low blood pressure — call 911 or go to your nearest emergency department right away. Do not drive yourself.
Your doctor may refer you for a colonoscopy, endoscopy, or blood tests depending on your symptoms. These tests help identify the source of bleeding and guide the right treatment. For a broader overview of digestive health, Healthline’s guide to gastrointestinal bleeding is a reliable resource.
Always speak with a qualified healthcare provider before drawing any conclusions about your symptoms. This article is for informational purposes only and is not a substitute for professional medical advice.
Frequently Asked Questions About Blood in Stool
Is blood in stool always a sign of something serious?
Not always, but blood in stool should never be ignored. The most common cause is hemorrhoids, which are usually harmless. However, it can also signal colorectal cancer, ulcers, or other conditions that need medical treatment.
What does dark or black stool mean?
Dark, tar-like black stool — called melena — is usually a sign of bleeding higher up in the digestive tract, such as the stomach or small intestine. This type of blood in stool is digested before it exits the body, which gives it a dark colour. It requires prompt medical evaluation.
Can medications cause blood in stool?
Yes. Common medications like ibuprofen, ASA (aspirin), blood thinners, and corticosteroids can irritate the stomach lining and cause digestive bleeding. If you notice blood in stool after starting a new medication, tell your family doctor or pharmacist right away.
How is the cause of digestive bleeding diagnosed?
Your doctor may order a colonoscopy, upper endoscopy, or blood tests to find the source of digestive bleeding. The type of test depends on whether the blood appears bright red or dark, and on your other symptoms. Early diagnosis leads to better outcomes.
Should I go to emergency if I see blood in my stool?
If you feel dizzy, faint, have a fast heartbeat, or feel very weak alongside blood in stool, go to the emergency room or call 911 immediately. For mild symptoms without dizziness, visit your family doctor or a walk-in clinic as soon as possible.
Are hemorrhoids the most common cause of rectal bleeding?
Yes. Hemorrhoids are the most common cause of bright red blood in stool or on toilet paper. However, your doctor will still want to rule out more serious conditions like colorectal cancer, especially if you are over 50 or have other risk factors.
Key Takeaways
Blood in stool can appear as bright red blood or dark, tar-like black stool — both need medical attention.
The most common cause of lower digestive bleeding is hemorrhoids, but colorectal cancer must always be ruled out.
Upper digestive bleeding is most often caused by peptic ulcers, gastric cancer, medication-related gastritis, or liver cirrhosis.
Medications like ibuprofen, ASA, and blood thinners can cause or worsen digestive bleeding.
Serious bleeds cause dizziness, low blood pressure, rapid pulse, and cold sweats — this is a medical emergency.
See your family doctor or a walk-in clinic for any rectal bleeding, even if you feel well.
If symptoms are severe, call 911 or go to your nearest emergency department right away.
Always consult a qualified healthcare provider for a proper diagnosis and treatment plan.
