Blackouts usually happen when you drink too much, too quickly. Your body cannot process a large amount of alcohol well.
During a blackout, you are conscious. You may hold conversations, laugh and seem quite alert. But later, you may not be able to remember any details of the event. This is also called alcohol-induced amnesia (memory loss).
A blackout is different from passing out. Passing out means you fall asleep or lose consciousness from drinking too much.
Effects of having a blackout
Blackouts happen when you are drunk.
You will have the usual risks associated with being drunk, such as:
- being more at risk of falls, accidents and injuries
- not making safe decisions - for example, having unprotected sex or driving drunk
- having fewer inhibitions - for example, dancing on a table
- having less control over your impulses
- being at risk of alcohol poisoning
Depending on how a blackout affects you, it can also cause problems for people around you.
Blackouts and behaviour changes
Blackouts can make your behaviour unpredictable. This can cause arguments and relationship problems with friends and family.
During a blackout, you may say or do things that are out of character. For example, you might be rude or insult someone. You may be aggressive to people around you, whether you know them or not.
Other people may not know you are having a blackout. You might hold what seems like a meaningful conversation with someone. But you forget this immediately. You may even forget you met the person. This can be hurtful for them.
You may never apologise to someone for an insult you do not remember giving.
Behaviour like this can cause long-term damage to relationships.
Causes of blackouts
Blackouts are often linked to binge drinking. If you drink too much too fast, your body may not be able to process (metabolise) the alcohol in your blood quickly enough. This high blood alcohol content (BAC) can increase your risk of a blackout.
Women are at higher risk of blackouts than men. This is because they usually weigh less and will reach high BAC levels faster than men.
Your risk of blackouts also increases if you drink while taking certain medicines. For example, medicine for anxiety or sleeping problems, such as diazepam.
Drinking on an empty stomach can also contribute to blackouts.
How a blackout happens
During a blackout you temporarily lose the ability to create and store new memories.
This is because alcohol disrupts the memory centre of the brain (hippocampus).
The memory centre stores and organises memories so that you can remember things later.
When you have a blackout, the alcohol blocks the transfer of memories from short-term to long-term storage in the hippocampus.
Types of blackout
There are 2 types of blackouts:
- total (en bloc blackout)
- fragmentary (partial blackout)
Total blackout
A total blackout is a severe type of blackout. It can last for hours. You do not remember anything that happens in that time. This is because you do not usually form memories. Or if you do form memories, you cannot access them.
Fragmentary blackout
A fragmentary blackout is a partial loss of memory after drinking. You may remember some things when you are reminded.
If you have a blackout
It can be frightening and worrying to find out you had a blackout.
Having a blackout does not mean you have alcohol-related problems such as alcohol use disorder or alcohol dependence.
But having even 1 blackout may prompt you into thinking about how you drink, and making a change.
If you are worried about your alcohol use, take our alcohol test.
Reduce your risk of blackouts
To reduce your risk of having a blackout:
- avoid binge drinking - stick to the weekly alcohol low-risk guidelines
- avoid drinking too quickly - sip rather than gulp
- avoid shots or drinking games
- alternate alcoholic drinks with non-alcoholic drinks
- never drink on an empty stomach - eat before and while you drink
If you had a blackout in the past, try to only drink in familiar situations. Make sure you have a plan for getting home.
Non-urgent advice: Get help with problem alcohol use
For confidential advice, freephone 1800 459 459.
If you think someone is having a blackout
It can be very difficult to tell if someone is having a blackout. They can often function as normal. For example, they can still eat, walk and hold conversations. But they have no memory of what is happening.
If you question them, they may not remember what happened even minutes earlier.
They may also repeat things they've just said. Or they may do things that are out of character.
If you think someone is having a blackout, stay with them or get them home safely.
If they are vomiting or have difficulty breathing, they could have alcohol poisoning. Get medical help immediately.
Emergency action required: Call 112 or 999 and ask for an ambulance if someone:
- has symptoms of alcohol poisoning
- loses consciousness from drinking alcohol