Alcohol, Memory Blackouts and the Brain

Blackouts Among Social Drinkers
by National Institute of Health

(Page 3 of 6)

Most of the research conducted on blackouts during the past 50 years has involved surveys, interviews, and direct observation of middle-aged, primarily male alcoholics, many of whom were hospitalized. Researchers have largely ignored the occurrence of blackouts among young social drinkers, so the idea that blackouts are an unlikely consequence of heavy drinking in nonalcoholics has remained deeply entrenched in both the scientific and popular cultures. Yet there is clear evidence that blackouts do occur among social drinkers. Knight and colleagues observed that 35 percent of trainees in a large pediatric residency program had experienced at least one blackout. Similarly, Goodwin reported that 33 percent of the first-year medical students he interviewed acknowledged having had at least one blackout. "They were inexperienced," he wrote. "They drank too much too quickly, their blood levels rose extremely quickly, and they experienced amnesia". In a study of 2,076 Finnish males, Poikolainen found that 35 percent of all males surveyed had had at least one blackout in the year before the survey.

As might be expected given the excessive drinking habits of many college students, this population commonly experiences blackouts. White and colleagues recently surveyed 772 undergraduates regarding their experiences with blackouts. Respondents who answered yes to the question "Have you ever awoken after a night of drinking not able to remember things that you did or places that you went?" were considered to have experienced blackouts. Fifty-one percent of the students who had ever consumed alcohol reported blacking out at some point in their lives, and 40 percent reported experiencing a blackout in the year before the survey. Of those who had consumed alcohol during the 2 weeks before the survey, 9.4 percent reported blacking out during this period. Students in the study reported that they later learned that they had participated in a wide range of events they did not remember, including such significant activities as vandalism, unprotected intercourse, driving an automobile, and spending money.

During the 2 weeks preceding the survey, an equal percentage of males and females experienced blackouts, despite the fact that males drank significantly more often and more heavily than females. This outcome suggests that at any given level of alcohol consumption, females - a group infrequently studied in the literature on blackouts - are at greater risk than males for experiencing blackouts. The greater tendency of females to black out likely arises, in part, from well-known gender differences in physiological factors that affect alcohol distribution and metabolism, such as body weight, proportion of body fat, and levels of key enzymes. There also is some evidence that females are more susceptible than males to milder forms of alcohol-induced memory impairments, even when given comparable doses of alcohol.

In a subsequent study, White and colleagues interviewed 50 undergraduate students, all of whom had experienced at least one blackout, to gather more information about the factors related to blackouts. As in the previous study, students reported engaging in a range of risky behaviors during blackouts, including sexual activity with both acquaintances and strangers, vandalism, getting into arguments and fights, and others. During the night of their most recent blackout, most students drank either liquor alone or in combination with beer. Only 1 student out of 50 reported that the most recent blackout occurred after drinking beer alone. On average, students estimated that they consumed roughly 11.5 drinks before the onset of the blackout. Males reported drinking significantly more than females, but they did so over a significantly longer period of time. As a result, estimated peak BACs during the night of the last blackout were similar for males and females. As Goodwin observed in his work with alcoholics, fragmentary blackouts occurred far more often than en bloc blackouts, with four out of five students indicating that they eventually recalled bits and pieces of the events. Roughly half of all students indicated that their first full memory after the onset of the blackout was of waking up in the morning, often in an unfamiliar location. Many students, more females than males, were frightened by their last blackout and changed their drinking habits as a result.

Use of Other Drugs During Blackouts

Alcohol interacts with several other drugs, many of which are capable of producing amnesia on their own. For instance, diazepam (Valium®) and flunitrazepam (Rohypnol) are benzodiazepine sedatives that can produce severe memory impairments at high doses. Alcohol enhances the effects of benzodiazepines. Thus, combining these compounds with alcohol could dramatically increase the likelihood of experiencing memory impairments. Similarly, the combination of alcohol and THC, the primary psychoactive compound in marijuana, produces greater memory impairments than when either drug is given alone. Given that many college students use other drugs in combination with alcohol, some of the blackouts reported by students may arise from polysubstance use rather than from alcohol alone. Indeed, based on interviews with 136 heavy-drinking young adults, Hartzler and Fromme concluded that en bloc blackouts often arise from the combined use of alcohol and other drugs. White and colleagues observed that, among 50 undergraduate students with a history of blackouts, only 3 students reported using other drugs during the night of their most recent blackout, and marijuana was the drug in each case.

About the Author

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