Increased daytime sleepiness enhances ethanol's sedative effects.

Thirty healthy men, 21 to 35 years old, received either 8.7, 13.0 or 17.4 mmol/kg (0.4, 0.6, or 0.8 g/kg) ethanol after 8 hours time in bed (TIB), one night of 5 hours TIB, and four nights of 5 hours TIB. Ethanol, administered as 80-proof vodka mixed 1:4 with tonic water, was consumed over 30 minutes (0900 to 0930 hours). Sleep latency was measured at 1000, 1200, 1400, and 1600 hours using standard sleep laboratory methodology. Breath ethanol concentration (BEC) was determined prior to each latency test. Mean latency to sleep on the four tests decreased from day 1 (8 hours TIB) to day 5 (fourth day of 5 hours TIB). On day 1 mean latency after 8.7 mmol/kg differed from that after 17.4 mmol/kg, with the 13.0 mmol/kg latency intermediate between the other two. On day 2 and day 5 during sleep restriction these dose differences were diminished. Latency on day 5 after 8.7 mmol/kg was similar to that of 13.0 mmol/kg on day 2, which was similar to that of 17.4 mmol/kg on day 1. The BEC did not change from day 1 to day 5 and significant dose differences between each dose remained consistent from day to day. These data show that increased basal levels of sleepiness enhance ethanol's sedative effects for even moderate ethanol doses.