Blacking Out: The Dangers & Causes

It’s not uncommon after a night out drinking or another similar event, for someone to tell you that they “completely blacked out” and can’t remember much, or anything of what they did and got up to.

It is often assumed that this is just a normal part of the drinking experience and a normal side-effect of consuming alcohol.

But in fact, there’s a lot of misunderstanding about what blacking out is exactly, what causes it, and what the dangers associated with it are.

This is a serious issue, because blacking out can be an indicator of excessive alcohol consumption, and can lead to serious consequences.

What is Blacking Out?

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Blacking out is a period, or periods, of amnesia or memory loss induced by high alcohol consumption and an increased level of alcohol concentration in the bloodstream. Someone who has blacked out won’t remember what they did or said during their blackout, and this can lead to confusion and distress.

Is Blacking Out the Same as Passing Out?

Blacking out is very different to passing out, but sometimes the two are conflated incorrectly. Passing out is usually indicative of a loss of consciousness (and this is often related to excessive alcohol consumption too), whereas blacking out refers to a loss of memory.

Because the two are both common side-effects of excessive alcohol consumption, they can go hand in hand and if you drank so much that you passed out, you might also find that you have a patchy memory caused by blacking out too.

What Causes Blacking Out?

Most commonly, blackouts begin when the blood alcohol concentration (BAC) reaches above-recommended levels. BAC is an indicator of how much alcohol has entered your bloodstream, effectively determining how drunk you are.

BAC levels can broadly be grouped into three or four categories, which show how symptoms of alcohol use change as the BAC increases:

  • BAC level 1: can be determined by symptoms like feelings of relaxation, improved self-confidence, and a very slight loss of motor control.
  • BAC level 2: characterised by the loss of inhibitions, feelings of tiredness, a slight decrease in heart rate, slight difficulty walking, and beginning to slur words or have distracted sentence formation.
  • BAC level 3: associated with a loss of consciousness, a loss of motor functioning (falling over and total inability to walk in a straight line or without stumbling), and a decreased heart rate. High BAC levels can be very serious, can be indicative of alcohol poisoning and can lead to extremely dangerous outcomes.

Generally, people will begin to experience blackouts when their BAC reaches 0.14%, which is around the second category of BAC level 2.

The blackouts are caused when the BAC increases rapidly, and it wears off when the BAC reduces to lower levels. During the period when the BAC is increased to around 0.14%, a person will experience partial or complete memory loss.

Blackouts can be grouped into two separate categories: en bloc blackouts, and fragmentary blackouts. Each has its own distinct indicators.

1. En bloc blackouts

En bloc blackouts are the total loss of memory during a period of time when BAC levels are high.

During this time of high BAC levels, memories aren’t correctly created, processed and stored. When the BAC levels reduce again, memory will return, but it will be impossible to recall events or memories from the time when the BAC was high.

2. Fragmentary blackouts

Fragmentary blackouts are less drastic than en bloc blackouts, and while you won’t immediately be able to recall the events, certain prompts and triggers (such as someone telling you “Do you remember when…”) may allow you to recall moments or images, while the full picture might still be inaccessible.

Therefore, Fragmentary blackouts are defined as partial or temporary memory loss that can be retrieved with the help of certain cues.

Why Does a Blackout Happen?

Blacking out is triggered when the BAC percentage reaches around the 0.14% mark, but why does it occur, and why does alcohol impact memory?

Blacking out is caused by the impact of alcohol interfering with and disrupting the processes and functions of the brain. One of the brain’s core functions is to create and store short-term memories based on sensory input and transfer them to long-term memory.

High levels of alcohol consumption impact the chemical processes occurring in the brain and can block the memory encoding process which moves short-term memories to long-term memory, and prevent the creation of new memories.

Specifically, alcohol changes with the ways in which receptors and neurons interact, meaning that signals aren’t correctly carried between them and that new memories cannot be formed as normal.

What Happens to the Body During a Blackout?

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While blackouts are a result of an interference in brain activity due to excessive alcohol consumption, the heightened BAC level which results in it will also have some symptoms and impacts on the body.

You might find walking difficult, making it more likely that you fall over and hurt yourself or get into an accident. You may find speaking difficult, which can make it hard to communicate with people and can lead to increased feelings of confusion.

Your reaction time will also be heavily impacted, which means that if you are doing any activities that require motor control your performance will be dramatically hindered.

However, despite these side effects, you will still mostly be able to hold conversations, walk and move about, and complete other simple activities that you would normally be able to do when drunk.

What are the Risks of Blacking Out?

Remember, just because you blacked out doesn’t mean you were passed out and unconscious. In fact, even though you might not be able to remember your activity during a blackout, doesn’t mean that you weren’t active during the period.

If you blacked out you will have been in a period of high BAC levels, which will mean that your inhibitions will have been low and your behaviour and judgment will have been impaired and different to what they normally are.

You will still have been completing activities and you will have been able to do most things. You just won’t be able to remember what you did.

This in itself is a serious risk and negative side-effect of blacking out. You may have held a highly emotional or combative conversation with a loved one, you may have committed some illegal activity, like vandalism or drink driving, or you may have even gotten into a fight.

If you are unable to remember any of these events, you are putting yourself at a greater degree of risk by not being able to recall what risky activities you may have taken part in.

Of course, blacking out doesn’t mean that you necessarily did anything that you might regret: it is simply an indicator of how much you drank. But the two do tend to go together because of the impact of alcohol on inhibitions and behaviour.

Can Blackouts Lead to Long-term Complications?

While blackouts themselves are only associated with memory, the heavy drinking that so often causes blackouts can have serious long-term impacts on your health and mental well-being.

Especially if you find that you’re blacking out regularly, this could be a serious indicator that you are drinking too much, too often.

The impacts of chronic excessive drinking can be widespread, and one of these effects is on an area of the brain called the frontal lobe. The frontal lobe controls cognitive processes and is also a component in the development of both short-term and long-term memory.

The damage that long-term excessive drinking can have on the frontal lobe also has an effect on the ability to recall memory, as well as its development.

Binge drinking, which is often the cause of blackouts, can also have long-term complications for other cognitive behaviours.

The frontal lobe also relates to your behaviour and personality, and binge drinking – which can damage the frontal lobe – can change the way in which you behave and your decision-making processes, and make your personality more unpredictable.

Which Demographics are Most at Risk of Blacking Out?

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Blacking out is a common experience among people who drink alcohol excessively, and regularly.

Of course, this can impact any person who drinks excessively, no matter their age, sex, or other demographic factors.

However, there are some groups of people who are more likely to blackout than others, because they are more likely to binge drink.

The people who are most likely to binge drink are people who are living with alcoholism. Among this substantial group, it’s middle-aged men who are most likely to regularly binge drink, and who are therefore most susceptible to blacking out.

Other than people with alcoholism, the demographic that is most likely to binge drink, and therefore blackout, is adolescents and young adults. This is especially common in young adults who are in their final years of high school and college, and in university.

In these settings, there is typically a culture of partying and drinking that begins to recede as people begin to get closer to their mid-twenties.

Because adolescents and young adults are still undergoing cognitive development, the risks associated with binge drinking, and therefore blacking out, are increased.

Alcohol, therefore, has greater long-term risks and binge drinking during cognitive development is shown to have an impact on memory and cognitive abilities.

Are Women More Likely to Blackout than Men?


It is also true that, as well as younger people, women are at a higher risk of blacking out than men. This is largely due to the differences between men and women when it comes to body composition and size.

Typically, men being larger than women with a higher proportion of muscle mass means that they require higher levels of alcohol to get drunk, and it takes more alcohol to increase the BAC.

These biological differences mean that the definition of binge drinking (and alcohol consumption guidelines more broadly) are also different for women than they are for men.

For example, the weekly recommended alcohol unit limit is lower for women than for men, and the threshold for binge drinking is also lower.

Is Blacking Out a Sign of Alcohol Use Disorder (AUD) or Alcoholism?

An alcohol use disorder (AUD) covers a spectrum of disorders that are associated with alcoholism.

An AUD isn’t just an unhealthy relationship with alcohol – though this is almost always an important precursor – it is characterised by a medical diagnosis of alcohol dependence, alcohol abuse, or alcohol addiction usually over the course of 12 months or longer.

Binge drinking itself, while dangerous, is not an AUD. This is because people can have a generally healthy relationship with alcohol, and binge drink very rarely as part of that.

Make no mistake, binge drinking is a negative behaviour that comes with risks, but it isn’t automatically a sign of alcohol abuse or a deeper problem.

However, a lot of people who do have an AUD, diagnosed or not, will binge drink regularly. Therefore, binge drinking and blacking out are key indicators of an AUD, even if not everyone who binge drinks has an alcohol use disorder.

Often, binge drinking and regularly blacking out are a symptom of more serious problems like alcohol dependence and can point towards a worrying lack of control when it comes to the substance.

This lack of control can either develop into alcohol dependence or alcoholism if not properly monitored and reflected on.

In summary, blacking out isn’t automatically a sign of an AUD. However, it is indicative of a lack of control when it comes to alcohol consumption, and people who do have an AUD will often binge drink, and blackout, regularly as part of this.

How Do You Prevent Blackouts from Drinking?

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If you want to prevent blackouts, that means you are serious about committing to a long-term, healthy relationship with alcohol. Luckily, the way to prevent blackouts is initially very simple: don’t exceed recommended drinking limits, and don’t binge drink.

There is no single magic trick or tip that will allow you to binge drink, have your BAC exceed 0.14%, and still avoid either en block blackouts or fragmentary blackouts. The only way to avoid them is to monitor your drinking and not reach this point at all.

This means that, if you are regularly blacking out and are worried about what it means for your relationship with alcohol and the future, you need to seriously reassess how you use alcohol and consider what change you need to make in the future.

For lots of people, this simply means drinking less. Try to bring your drinking in line with the recommended alcohol guidance from the UK Chief Medical Officer, which is no more than 14 units per week.

If you’re struggling to do this, you should talk to your family and friends and share your goal with them. Tell them upfront that you are trying to reduce the amount of alcohol you drink in order to avoid binge drinking; tell them that you’re worried about how often you’re blacking out, and the long-term risks.

They will do their best to support you, and be a good influence.

If you don’t drink often, but you do binge drink and find it hard to keep that under control, you should also keep the Chief Medical Officer’s advice in mind that your 14 units a week should be spread over three days or more.

Spreading your drinking out will ensure that you don’t binge drink, and the only thing you have to do is keep a track of what you’re consuming, how much, and when.

The Dangers & Causes of Blacking Out: A Summary

Blacking out is when you struggle to remember, or are completely unable to remember events that occurred while you were drinking.

This happens when your BAC levels reach around 0.14% because the alcohol impairs your brain’s ability to correctly process and store memories.

There are two types of blacking out: one which causes complete and irretrievable memory loss, and one which causes fragmented, temporary memory loss.

You are at the greatest risk of blacking out when binge drinking.

Binge drinking comes with many long-term physical and psychological risks, and regular excessive alcohol consumption can damage the brain and lead to a decline in health.

The best way to prevent blacking out is to avoid binge drinking. This can be achieved by tracking your consumption of alcohol and making sure it’s spread out evenly over the course of a week.

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[1] Does binge drinking between the age of 18 and 25 years predict alcohol dependence in adulthood? A retrospective case-control study in France

[2] The Risks Associated With Alcohol Use and Alcoholism