What Is an Alcohol-Induced Blackout?

An alcohol blackout, also known as alcohol-induced amnesia, occurs when someone drinks enough to trigger some degree of memory loss. A person may lose an entire block of time, such as a few hours, or may have patchy memories of that period of drinking. The latter is more common. Blackouts occur when someone drinks enough alcohol, quickly enough, to become inebriated to a certain degree. Exactly how drunk or how much alcohol it takes to black out cannot be defined; it varies by individual and situation.

Experiencing alcohol-induced blackouts is extremely dangerous. It can cause accidents, risky behaviors and poor judgement, and increases the risk of developing an alcohol use disorder and physical health problems. Blacking out is not just something that happens to alcoholics—it is a serious and harmful effect of drinking too much that can affect anyone.

A blackout is a period of memory loss and it can be caused by drinking too much alcohol too fast. How much alcohol it takes to cause a blackout varies depending on each individual. In general, blackouts occur when a person’s blood alcohol concentration, or BAC, reaches 0.20 to 0.30. This is well over the BAC, 0.08, at which a person is considered to be inebriated and unable to drive in most states. Factors like gender, size, what someone has eaten, the strength and size of drinks, and speed of drinking affect how much alcohol it takes to reach levels that can lead to blackouts.

Alcohol acts in the brain in several ways, but in terms of memory loss it is the disruption of the hippocampus that is thought to be the root cause. This brain region is where new memories are formed and stored. Alcohol seems to disrupt the process of turning short-term memories into long-term memories. It does not destroy older memories but simply disrupts the process of forming new ones.

This may explain why most people in a blackout state are not actually passed out and often appear to be in control and fully aware. The way alcohol impacts the hippocampus means that a person in a blackout can remember what is happening around them for a few minutes, but then the memory is gone. They may repeat themselves for this reason, but otherwise seem to be functioning well. The more alcohol consumed, the more severe the long-term memory loss.

Alcohol-induced amnesia was once considered to be a problem mainly of people with severe alcohol use disorders. Research has determined that it is much more common than previously believed and happens to all kinds of people with various drinking habits and patterns.

• A study of nearly 800 college students found that more than half had experienced a blackout.
• Those college students reported finding out later they had engaged in a range of behaviors they didn’t remember, including driving, vandalizing property, having unprotected sex, and making purchases.
• Blackouts have been observed in study participants at BACs as low as 0.14.
• Women are at greater risk of experiencing blackouts when drinking than men.
• People who have had blackouts previously are more likely to experience them again.

It is thought that some people are inherently more vulnerable to blacking out when drinking.

Loss of memories after drinking can occur in one of two ways: as an en bloc or a fragmentary blackout. Fragmentary blackouts are more common and can be thought of as like brownouts; the lights dim but don’t go fully out. A person experiencing this kind of blackout can remember certain parts of the previous night, or drinking binge, but not others. It is a fragmentary memory with bits and pieces coming through and others lost. Those lost pieces may return with cues or when someone else describes them.

An en bloc blackout is less common. This happens when someone cannot remember anything from when inebriated. These memories cannot be recovered by hearing about what happened or with time; they are simply gone. This is sometimes considered a true blackout, and the memories don’t return because they were never stored in the brain.

When an individual experiences a blackout, he or she has drunk a significant amount of alcohol, resulting in impairment and poor judgment. There are a number of potential complications that can occur because of these effects, ranging from mild to severe with lasting consequences:

• Driving or operating equipment and causing an accident or harm to someone
• Suffering an injury from falling or having any type of accident
• Having unprotected sex, which can result in unplanned pregnancies and sexually transmitted diseases
• Getting in fights or being a victim of assault
• Saying or doing things that damage relationships
• Getting into trouble with the police, being arrested, and facing incarceration or legal issues
• Spending too much money

An alcohol-induced blackout leaves a memory hole that cannot ever be recovered, but the harm to the brain may go well beyond this momentary lapse. Binge drinking and repeated blackouts have been found in studies to interfere with the ability to learn new information. The people who engaged in binge drinking did not perform as well as control groups in tests of verbal declarative memory, which could impact academic performance. The impairment may be a result of damage to parts of the brain responsible for memory, but the actual reasons are not well understood.

Another study found that a pattern of drinking to the point of blackout is connected to changes in how the brain develops in young people. Because the brain is still developing, drinking at all but especially drinking excessively is particularly risky for adolescents and teens.

Drinking enough to black out is drinking too much and can be considered binge drinking. Doing it repeatedly can be a real problem and can contribute to significant long-term health problems. For instance, the more frequently a person drinks to blackout, the more likely he or she is to develop an alcohol use disorder. An alcohol use disorder is a long-term issue that must be treated and managed for years to avoid relapsing.

Other long-term problems that are associated with regular binge drinking include liver damage and liver disease, heart disease, high blood pressure, stroke, arrhythmias, cardiomyopathy, pancreatitis, and a weakened immune system. Drinking too much increases the risk of developing certain types of cancers and infections like pneumonia.

Changing Drinking Behaviors

For many people, blacking out once is a frightening experience that leads to changes in drinking patterns. It can often be enough of a trigger to lead a person to drink less and more slowly in the future. For some people this change can be difficult to make, and an inability to moderate one’s drinking may be indicative of a substance use problem.

Anyone can take steps to drink less and avoid blackouts, such as avoiding liquor and strong drinks, setting a drink limit, or abstaining in particular situations that have led to binge drinking in the past. For someone who tries but fails to use strategies to moderate drinking, professional help may be needed. Working with an addiction counselor or therapist, attending support group meetings, or even entering a residential alcohol addiction treatment facility can help someone who wants to change their drinking patterns but is struggling to do it alone. Blackouts are dangerous in many ways, and it is important to make changes to avoid experiencing them in the future.