"Some people think that blackouts, very bad hangovers, and outrageous behaviour at parties are very funny," explained Marc A. Schuckit, distinguished professor of psychiatry at the University of California, San Diego, and corresponding author for the study. "This does not represent 'fun.' People don't understand how dangerous blackouts are. In fact, people have oodles of misconceptions about drinking."

Blackouts occur when a person's blood alcohol concentration (BAC) is likely significantly above what is considered 'legal intoxication.' The higher one's alcohol levels, the greater the chance of a blackout.

"Someone who has had a blackout cannot remember part of their drinking episode," said Schuckit. "As you can imagine, blackouts are likely to occur when the drinker is vulnerable to a range of additional dangerous consequences. Women might have unprotected sex, place themselves in a situation where they can be raped, or not be fully capable of protecting themselves. Men can get into fights, use very bad judgement regarding another person, and are often the driver when BACs associated with blackouts can lead to a car accident. Blackouts are very dangerous for both men and women."

Schucki added that this is the first study to examine blackout trajectories over time for this age group. "We selected 15- to 19-year-olds because the heaviest drinking usually occurs from 15 to around 22 years of age. Also, our sample is huge."

Schuckit and his colleagues evaluated the pattern of occurrence of ARBs across four time points - ages 15, 16, 18, and 19 - for 1,402 drinking adolescents (837 females, 565 males) from the Avon Longitudinal Study of Parents and Children (ALSPAC) in Bristol, England. Multinomial regression analyses evaluated age-15 predictors of ARB trajectories, including demographic factors, substance-related items, impulsive-like characteristics, and estimated peer substance use.

"Our results showed that blackouts were common and repetitive in these young British subjects," said Schuckit. "For example, 30 percent of those who drank reported ARBs at age 15, and 74 percent reported ARBs at age 19. Almost half of our sample not only had blackouts during the four total years of our study, but also had blackouts every time we followed up with them, approximately every one and a half years."

The researchers identified four trajectory classes. Class 1 (5.1%) reported no blackouts from age 15 to 19. For Class 2 (29.5%) ARBs rapidly increased with age. For Class 3 (44.9%), blackouts slowly increased. Class 4 (20.5%) reported ARBs at all four time points. Age-15 predictors of CLASS 4 included being female, having higher drinking quantities, smoking, impulsive-like characteristics, and higher estimated peer-substance involvement.

"The UK ranks among the top for drinking in the world, beginning by mid to late teens," said Schuckit. "Drinking rates in the US are not quite as high, but I am guessing that by age 19, more than half would have likely had a blackout. Regardless the nation, what we're trying to understand here is the impact of blackouts, and what may predict a blackout. No matter what country, when kids are drinking, they are not likely to understand what is going on with their systems and how dangerous it can be. And if they're drinking to the point of having blackouts, this is dangerous."

Schuckit recommended that teens be helped to understand more about the dangers of their drinking. "Kids have to recognize the problem of blackouts themselves and take steps to change behaviors," he said. "We need to identify something they can recognize in themselves and their peers so they can learn to modify their behaviors, because blackouts are dangerous, prevalent, and persistent."