Stroke Causes

There are several known causes and risk factors of stroke. Strokes are the result of an interruption of blood flow to the brain. They are often caused by existing conditions, such as heart disease, diabetes, and infection. This article discusses these and other common causes of stroke.

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Common Causes of Stroke

Often, the cause of a stroke is known and can be identified with a medical history or with diagnostic testing. It is also common for a person to have several different risk factors that could be responsible for a stroke, and often, having several risk factors makes it more likely to have a stroke. 

Cerebral Causes of Stroke

Sometimes, it is disease in the brain that causes a stroke.

  • Cerebrovascular disease: Disease of the blood vessels in the brain, often due to long term hypertension, high cholesterol, or diabetes, can make the blood vessels more likely to become blocked.
  • Brain aneurysm: An outpouching of an artery in the brain may leak or rupture, causing a hemorrhage.
  • Arteriovenous malformation (AVM): A malformed group of connected blood vessels, usually containing arteries and veins. An AVM may rupture or form a thrombus, causing a hemorrhagic or ischemic stroke. 
  • Vasospasm: When an artery suddenly spasms, it disturbs blood flow and causing ischemia even in the absence of a blood clot.

Cardiac Causes of Stroke

It is very common for a stroke to be caused by heart disease.

  • Arrhythmia: An irregular heart rhythm such as untreated atrial fibrillation can promote the formation of a blood clot and cause an embolus to travel to the brain.
  • Heart attack: Lack of blood supply to the brain due to a sudden reduction in heart function may cause either a watershed infarct or may cause an embolus to travel to the brain.
  • Carotid Artery Disease: When disease or blood clots develop within the blood vessels located in the neck that supplies the brain, an embolus from the carotid artery or blockage of the carotid artery can cause a stroke.
  • Hypertension: Long term high blood pressure contributes to cerebrovascular disease, carotid artery disease, and heart disease. Additionally, sudden extreme episodes of hypertension may cause vasospasm or hemorrhage of an aneurysm.

Systemic Causes of Stroke

Sometimes, diseases of other organs or medical conditions that affect the whole body can cause a stroke.

  • Hypotension: Low blood pressure can occur due to severe blood loss or dehydration, causing hypoperfusion of the brain and watershed stroke.
  • Medication: A high dose of medications that affect blood clotting, bleeding or blood pressure can lead to a stroke.
  • Drugs: Illegal drugs such as cocaine, methamphetamine, and other powerful stimulants can cause vasospasm of any artery in the body. This can cause a heart attack, a stroke due to vasospasm of cerebral arteries, or the dislodging of a blood clot that can travel to the brain, causing a stroke.
  • Blood clotting disorders: Disease that causes excessive bleeding or blood clotting can cause a hemorrhagic stroke or an ischemic stroke.
  • Infection: Severe infections can alter the body’s blood clotting or bleeding susceptibility, leading to a thrombus, an embolus or a hemorrhage. In rare instances, an infectious organism can actually physically block a blood vessel, causing ischemia.
  • Inflammation: Some inflammatory diseases can contribute to increased blood clotting.
  • Air embolus: An air bubble that travels to the brain from somewhere else in the body, obstructing a blood vessel, and causing a stroke.

Interruption of Blood Flow to the Brain

When blood flow within a blood vessel is interrupted, the nearby region of the brain is deprived of oxygen and vital nutrients. This is called ischemia. The immediate consequence is that the lack of blood makes it difficult for the affected region of the brain to function. If the lack of blood flow is very brief, and then restored, a reversible stroke, also called a TIA or a mini-stroke will ensue. If blood flow is not quickly restored, the injury will become more extensive- possibly permanent, resulting in an ischemic stroke.

There are a number of ways that blood flow can be interrupted in the brain.

Blood Clot

Interruption of blood flow may occur due to a blood clot, called a thrombus or an embolus.

  • Thrombus: A thrombus is the partial or complete clogging of an artery due to a blood clot.
  • Embolus: An embolus is a blood clot that initially forms in an artery, and then loosens and travels until it reaches an artery in the brain, causing blockage and damage in the brain.


Another cause of stroke is a bleeding on the brain. When a blood vessel is torn, blood leaks out, causing irritation to the nearby brain tissue. When the blood vessel is severed and blood loss occurs, there is also inadequate blood supply to the target destination in the brain. A stroke caused by bleeding from a leaking or torn blood vessel is a hemorrhagic stroke.


Low blood supply to the brain is a less common cause of stroke. When the fluid or blood volume in the body is exceptionally low, the brain may not receive enough blood. While there is no blood clot in this instance, the brain suffers because the areas of the brain that are normally supplied by extensions of tiny branched arteries may not receive an adequate blood supply. A stroke resulting from low blood supply is usually called a watershed stroke. Certain areas of the brain are more susceptible to a watershed stroke.

A Word From Verywell

There are a number of known causes of strokes, and there are also strategies that can prevent a stroke, including getting screening tests that can assess your stroke risk.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.