Your friend is likely to be telling you the truth. Drinking alcohol can affect memory, ranging from mild impacts through to significant blackouts. Alcohol-induced blackouts are defined as amnesia or memory loss for all or part of a drinking episode. When these occur, the person can be conscious and appear to interact completely normally with those around them. What makes blackouts so hard for people to understand is that it can be difficult or impossible to know whether a person is experiencing one. They're like headaches, no-one can really know whether you have one or not, the experience is happening inside the brain.
Memories are formed by something happening and the short-term memory of what just occurred being 'imprinted' into a long-term memory. Alcohol disrupts this 'imprinting' - you can walk, talk and answer questions, but memories of this are prevented from being imprinted into events you will be able to remember an hour later or the next day.
A person who has passed out has lost consciousness and is unable to respond to what is going on around them. If someone has been drinking and becomes unconscious, medical assistance should be sought immediately.
It used to be thought that only heavy, long-term drinkers experienced blackouts but we now know that they are quite common among many who choose to drink alcohol. They are more likely to occur when people drink to excess, with gulping drinks and drinking on an empty stomach, causing a rapid rise and high peak blood alcohol concentration (BAC), increasing the risk. Recent Australian research found that adolescent females are more likely than males to experience these memory losses. This is thought to be due gender differences around the ability to process alcohol and body composition.
Although it is not always the case, blackouts and memory lapses usually occur only when significant amounts of alcohol have been consumed. When your friend cannot remember what happened the night before this is likely to be a warning sign that they are drinking too much - it is not simply a 'part of the alcohol experience'. If they ever experience a blackout when drinking, whether it be for a minute, an hour or whatever – try to get them to pull back and drink a little less. Periods of memory loss potentially puts you at great risk and, sadly, there are those who may take advantage of this type of situation.
First published: July 2021