Alcohol-induced amnesia, more commonly referred to as “blacking out” or being “blacked out,” describes temporary memory loss from heavy drinking. Black outs are brought on by a rapid increase in blood alcohol concentration (BAC) levels. This is a consequence of binge drinking. The National Institute of Alcohol Abuse and Alcoholism (NIAAA) defines binge drinking as having five or more drinks within two hours for men and four or more drinks within two hours for women. Black outs typically won’t occur until a person’s BAC has reached .14 percent or higher. Alcohol-induced black outs can be very scary. You might wake up after a night of drinking and not remember how you got where you are. You might not remember risky behaviors such as driving your car while intoxicated, engaging in unprotected sex, or being sexually assaulted.

Many people do not experience unconsciousness or passed-out drunk until BAC has reached nearly .3 percent. Even though you are incapable of creating new memories during a black out, a person in a black out is still capable of having conversations, making decisions, and even driving a car. Excessive consumption of alcohol causes certain parts of the brain to work less effectively. At the same time, dopamine and norepinephrine levels are rising. This is why you might feel buzzed or stimulated while drinking, even though alcohol is a depressant.

So, why do you black out when you drink?

Our ability to think rationally and make sound decisions lives in the prefrontal cortex. As your BAC rises, your prefrontal cortex is significantly impacted. A blacked-out person might eventually pass out or lose consciousness, but one is not necessarily always correlated with the other. Your gender and genes play a large part in whether or not you are prone to blacking out. One might black out but not pass out, and in less common situations, one might pass out without having blacked out.

With inhibitions lowered, someone under the influence of alcohol is at a much higher risk of making dangerous decisions. Driving drunk, having unprotected sex, destroying property, getting into arguments or physical fights, or being sexually assaulted are examples. According to the NIAAA, 25 percent of women in the United States have experienced sexual assault. “Approximately one-half of those cases involve alcohol consumption by the perpetrator, victim, or both.” According to the National Highway Traffic Safety Administration, 10,874 Americans died in drunk driving accidents in 2017. It also reported that having a BAC of .15 percent — nearly twice the legal driving limit of .08 percent and the same BAC when black outs begin — will result in “substantial impairment in vehicle control, attention to driving task, and in necessary visual and auditory information processing.”