Interrupted Memories: Alcohol-Induced Blackouts

Drinking to the point of a blackout has gained pop culture notoriety in recent years. Alcohol-induced blackouts can lead to impaired memory of events that transpired while intoxicated, and a drastically increased risk of injuries and other harms. They can occur in anyone who drinks alcohol, no matter their age or level of experience with drinking. In this factsheet, we will take a sober look at this common but deeply concerning consequence of alcohol misuse.

Alcohol misuse can prevent the hippocampus from forming memories, brain image

What Are Blackouts?

Alcohol-related blackouts are gaps in a person’s memory for events that occurred while they were intoxicated. These gaps happen when a person drinks enough alcohol to temporarily block the transfer of memories from short-term to long-term storage—known as memory consolidation—in a brain area called the hippocampus.

Types of Blackouts

There are two types of blackouts; they are defined by the severity of the memory impairment. The most common type is called a “fragmentary blackout” and is characterized by spotty memories for events, with “islands” of memories separated by missing periods of time in between. This type is sometimes referred to as a grayout or a brownout.

Complete amnesia, often spanning hours, is known as an “en bloc” blackout. With this severe form of blackout, memories of events do not form and typically cannot be recovered. It is as if the events simply never occurred.

When Do Blackouts Occur?

Research indicates that alcohol-induced blackouts are more likely to occur when someone drinks on an empty stomach, drinks quickly, or engages in binge drinking, which can all lead to a rapid rise in blood alcohol concentration (BAC).

Blackouts are also more likely to occur if someone takes certain medications such as those for sleep and anxiety. Because females, on average, weigh less than males and, pound for pound, have less water in their bodies, they tend to reach higher peak BAC levels than males with each drink. Females also reach peak BAC levels more quickly. This helps explain why females appear to be at a higher risk for having blackouts.

Drinking enough alcohol to cause blackouts can be dangerous. Many cognitive abilities beyond memory such as impulse control, attention, judgment, and decision-making are significantly impaired at high BAC levels.

Blackouts vs. Passing Out

A blackout is not the same as “passing out,” which means either falling asleep or losing consciousness from drinking too much.

During a blackout, a person is still awake but their brain is not creating new memories. Depending on how much the person drank, it is possible to transition from having a blackout to passing out.

Are Blackouts a Sign of an Alcohol-Related Problem?

Research among college students and other young adults has shown that the frequency of blackouts predicts other alcohol-related consequences (such as missing work or school, having a lower grade point average [GPA], being injured, ending up in the emergency room, getting arrested, or experiencing other negative outcomes). Questions about blackouts during routine medical visits could serve as an important simple screen for the risk of alcohol-related harms.

Blackouts are not necessarily a sign of alcohol use disorder, but experiencing even one is a reason for concern and should prompt people to consider their relationship with alcohol and talk to their health care provider about their drinking.