There's been a lot of talk lately about drinking and memory, particularly about blackouts during heavy drinking. As he was questioned about allegations that he engaged in sexual assault while drunk in high school, Supreme Court nominee Brett Kavanaugh denied ever blacking out. This may clear up some misconceptions.

What does it mean to black out while drinking?

First, it does not mean that you pass out or become unconscious. In fact, by definition, people who have had alcohol-related blackouts have retained consciousness, said Reagan Wetherill, a University of Pennsylvania psychologist who does addiction research. "A person in a blackout is conscious and interacting with their environment," she said.

What happens?

Reagan Wetherill studies addiction at the University of Pennsylvania.
Courtesy of Penn Medicine
Reagan Wetherill studies addiction at the University of Pennsylvania.

Alcohol has broad effects on the brain regions involved in creating new memories, Wetherill said. It affects not only the hippocampus, the brain's memory center, but all the other parts of the brain that help transfer information. "The brain itself is not creating memories," Wetherill said. Drinkers may be able to participate in events, even emotionally charged ones, that they are unable to remember later. They may have partial amnesia – remembering some details but not others – or complete loss of memory for larger blocks of time.

Even in the absence of blackouts, alcohol impairs the formation of long-term memories. The more you drink, the more your memory is affected.

Who's at risk?

Some people may be more genetically vulnerable to blackouts than others. The risk seems to be higher for people with a family history of problem drinking, Wetherill said.

Blackouts are more common in people who drink quickly or on an empty stomach. In one small study of 50 students who said they had blacked out, most said they had been drinking liquor alone or combined with beer. Just one reported drinking nothing but beer. Because of their body composition, women are more susceptible than men, Wetherill said.

If you blacked out while drinking, how would you know?

You might not, Wetherill said. If you can't remember the whole night or a big chunk of it, you'd probably figure that out. If you forgot a smaller chunk of time or details of an incident, you might not know what happened unless someone told you. Some people find they have "hazy" memories when friends describe what happened.

If someone is drunk enough to vomit, are they more likely to experience blackouts?

Vomiting is generally associated with higher blood alcohol concentrations (BAC), from 0.09 to 0.25, Wetherill said. (In Pennsylvania, your driving is considered impaired at 0.08.) Studies have found blackouts in people with BACs as low as 0.06, but most, she said, found them more common at 0.14 and above.

Is a young drinker who has blacked out more likely to become a problem drinker?

Blackouts were once considered a sign of alcoholism. This is no longer true. Studies have shown that blackouts are common in college students. One found that about half of college students who had ever consumed alcohol said they had blacked out at some point.  Wetherill said drinking tends to rise sharply when young people get to college and reach drinking age. Current studies have found that many people age out of heavy drinking as they take on more adult responsibilities like parenthood and jobs. Some young heavy drinkers, of course, do develop alcohol-use disorder.  That needs more study, but Wetherill said it is because of a constellation of factors that go well beyond high school and college binge drinking.