Individual differences in the sedating effects of ethanol

Twenty-four healthy, normal-sleeping, males aged 21-35 were screened for basal levels of sleepiness using the Multiple Sleep Latency Test (MSLT). Twelve subjects had basal average daily sleep latencies of less than or equal to 6 min (sleepy) and 12 had latencies of greater than or equal to 16 min (alert) on the MSLT. Subjects consumed either ethanol (0.75 mg/kg) or placebo at 0900-0930 after spending 8 hr time in bed (TIB) the previous night. Sleep latency was measured at 1000, 1200, 1400, and 1600 hr. Divided attention performance and the Stanford Sleepiness Scale (SSS) were assessed at 1100 hr. Breath ethanol concentration (BEC) was determined prior to each latency test. Ethanol decreased average daily sleep latency, divided attention scores and SSS ratings. There were individual differences in the sedating and impairing effects of ethanol, related to subjects' basal level of sleepiness/alertness. The alert subjects exhibited longer sleep latencies and higher performance scores after ethanol administration than the sleepy subjects after placebo. Subjectively the groups had a similar level of sleepiness on placebo and were similarly sedated with ethanol.