Fainting | Causes & Risk Factors


What causes fainting?

Fainting, which is also called syncope, can be caused by many different things. Sometimes a specific cause for fainting cannot be found.

A sudden drop in your blood pressure can cause you to faint. Sometimes your heart rate and blood vessels can't react fast enough when your body's need for oxygen changes. This is very common among older people and in people who have certain health conditions, such as diabetes. Fainting can happen when:

  • You stand up too fast.
  • You work or play hard, especially if it's very hot.
  • You begin to breathe too fast (called hyperventilating).
  • You get very upset. Being upset can affect the nerves that control your blood pressure.
  • You're taking medicine for high blood pressure.

Coughing, urinating and stretching can also get in the way of the flow of oxygen to the brain and may cause you to faint. If you faint once during one of these activities, it's probably not something to worry about. But if it happens more than once, tell your doctor about it.

If you faint when you turn your head to the side, the bones in your neck may be pinching on one of the blood vessels that leads to your brain. If this happens to you, be sure to tell your doctor about it.

A drop in your blood sugar may also cause you to faint. This can happen if you have diabetes, but it may also happen if you don't eat for a long time.

Some prescription medicines can cause fainting. Be sure to talk to your doctor if you think your fainting may be related to a medicine you're taking. Alcohol, cocaine and marijuana can also cause fainting.

More serious causes of fainting include seizures and problems with the heart or with the blood vessels leading to the brain.

Who is at risk for fainting?

People who have certain medical conditions are more likely to faint. These conditions include:

  • Heart problems such as an irregular heartbeat or blockages in or near the heart that block the blood from getting to the brain
  • Diabetes
  • Anxiety or panic disorders
  • Dehydration
  • Low blood sugar

Written by familydoctor.org editorial staff

Reviewed/Updated: 03/14
Created: 09/00