• Basics

    Fainting is a temporary loss of consciousness caused by reduced blood flow and oxygen to the brain. Fainting, or “passing out”, can occur in otherwise healthy people, or it may indicate serious underlying disease that requires treatment. Many things can cause a person to faint, including epilepsy, internal bleeding, head injuries, low blood pressure, and low blood sugar associated with diabetes medications. This article focuses on fainting that is caused by reduced blood flow to the brain.

    Fainting can occur with or without warning, and may result in injuries. Between 16% and 35% of people who faint injure themselves when they fall. Most injuries are minor, such as cuts and bruises, but bone fractures and serious injuries from automobile or industrial accidents also occur after episodes of fainting.

    Fainting is common in the US, accounting for approximately 3% of emergency room visits and up to 6% of hospitalizations each year. Approximately half of the US population will experience one episode of fainting sometime during their lives. For most people, fainting is an isolated event, but about one-third of people who faint experience recurring episodes.

  • Causes

    Fainting can be caused by any condition that results in reduced blood flow to the brain. As such, fainting has many potential causes, and determining which one is responsible can be a challenge. Many causes of fainting, especially in young people, are relatively harmless. However, others causes, such as heart disease, can be life-threatening if left untreated. Accurate diagnosis is essential to determine a patient’s risk and course of treatment.

    Heart disease is one of the most serious causes of fainting. Abnormal heart rate or irregular heart rhythm (arrhythmia) can reduce the efficiency of the circulatory system, and result in a sudden drop in blood flow to the brain. People who faint as a result of these heart conditions tend to be older than 65 years of age.

    Other cardiac conditions that cause fainting, such as pulmonary embolism or a blocked artery, lower the blood pressure or disrupt blood flow to the brain. Fainting resulting from these causes often occurs during or after exercise, and affects young people (especially athletes) as well as older adults.

    One relatively harmless form of fainting is caused by a nervous system response that reduces blood pressure and blood flow to the brain. This type of fainting usually occurs while a person is standing, and is often triggered by fear, stress, or pain. It may recur in specific situations such as urinating, defecating, or coughing.

    This type of fainting occurs most often in children and young adults, but it may occur at any age. It typically occurs after two or three minutes of symptoms such as a sensation of warmth, nausea, lightheadedness, dizziness, blurred or faded vision, or stomach upset. If the person reclines, restoring the blood flow, he or she can recover within a few minutes.

    Other things can cause a person to “pass out” that are not covered in this article. Epilepsy, internal bleeding, head injuries, low blood pressure, and low blood sugar associated with diabetes medications can all cause a loss of consciousness. This article, however, focuses on fainting caused by a reaction to stress or underlying heart disease.

Recommended Reading

Meet the Pharmacists

I'm Kristen Dore, PharmD. Welcome to PDR Health!

Check out my latest blog post on heartburn medication