What is a blackout?
A blackout is a temporary loss of consciousness. In a blackout, you experience a loss of memory. There are many different causes of blackout – it might be an effect of drugs or alcohol, a problem with circulation, or a problem within the brain, such as epilepsy.
It may not be serious, but it is important to see your doctor and try to establish the underlying cause.
Sometimes, people experience memory loss and describe this as a blackout – for example, after they have drunk a lot of alcohol or taken illicit drugs.
What causes a blackout?
One common cause of a blackout is fainting. Fainting occurs when your heart rate drops and your blood vessels widen, resulting in low blood pressure. It can happen when you are very hot, distressed, in severe pain, you see or smell something unpleasant, or while you are coughing or going to the toilet. Sometimes, you might black out when you stand up too quickly. This is because your blood pressure suddenly drops.
Blacking out can also be caused by a serious health condition, including:
- arrhythmia (abnormal heart rhythm)
- heart disease
- problems with the blood vessels in the brain
- some mental illnesses
- a seizure
- low blood sugar
- illicit drugs
- some medicines
How are blackouts prevented and treated?
Treatment will depend on the cause of your blackout. For example, if it was caused by a heart rhythm problem, there are medicines that may help prevent you from having another one. However, it is not always possible to prevent blackouts.
If you feel faint, lie down or sit with your head between your knees. Make sure you stand up or change position slowly.
If you have had a blackout caused by fainting, try to avoid triggers like standing for too long or getting dehydrated.
Blackouts caused by alcohol
People can black out because they have drunk a lot of alcohol. In this case, the term blackout refers to memory loss. When they sober up, they cannot remember what happened while they were drunk. This is because the brain cannot form new memories when the alcohol in your blood reaches a certain level. The more you drink, the more memory you lose.
Drinking enough to cause a blackout will also cause problems with your walking, talking, standing, judgement and vision.
You are more likely to black out from alcohol if you drink on an empty stomach or if you drink too much too quickly. To avoid blacking out from alcohol, make sure you drink slowly and do not drink too much. Take sips of water between sips of alcohol, and eat food while you drink. Avoid binge drinking.
Drinking so much that you black out can cause physical, social and mental problems. It can lead to accidents and injuries, alcohol poisoning, fights and long-term health issues. If you need help with alcohol, visit:
- DrinkWise Australia website
- the Alcoholics Anonymous (AA) Australian website, or call 1300 222 222
- healthdirect’s page on Managing your alcohol intake
When should I seek help for a blackout?
If you have blacked out and you do not know why, you should always seek medical attention. It could be a sign that something is seriously wrong, and it is a common cause of injuries, especially in older people.
If you see someone else black out, raise their legs above the level of their head, loosen tight clothing and seek medical attention.
If you are with someone who is unconscious, call triple zero (000) for an ambulance, and if the person stops breathing, start CPR.
Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: January 2021