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Research Summary

Late Nights and Drinking, Even Moderate Amounts, Impair Driving

Alcohol use and sleepiness are both risk factors for driving injuries and fatalities. Researchers in this study examined how the combination of drinking and sleepiness influenced driving performance in 29 young adults.

Subjects stayed awake several hours after usual bedtime and consumed, over 30 minutes 1 hour before usual bedtime, vodka* on one night and placebo on another. They completed driving simulation and visual reaction time tasks before and after consuming the alcohol or placebo. Analyses were adjusted for potential confounders (e.g., previous sleep history).

  • Performance on the driving simulation task significantly deteriorated as the time awake increased.
  • Alcohol exacerbated the effects of wakefulness on certain driving simulation tasks, particularly at hour 15.5 of wakefulness (when alcohol levels peaked) but not at hour 18.5.
  • Reaction time also deteriorated with increasing time awake, but was not significantly affected by alcohol consumption (compared with placebo).


In this study, drinking on top of sleep deprivation decreased driving performance. But, drinking did not appear to exacerbate sleep deprivation’s effects on reaction time. By 18.5 hours of wakefulness, the effects of sleepiness apparently superseded any alcohol effects. This study provides additional evidence that in sleep-deprived young people, the rapid consumption of even a moderate amount of alcohol may further impair driving. The potential effects of less-rapid consumption of alcohol or of eating food in conjunction with alcohol intake were not tested.     

R. Curtis Ellison, MD

*0.54 g/kg for men; 0.49 g (mixed with tonic)/kg for women


Rupp TL, Acebo C, Seifer R, et al. Effects of a moderate evening alcohol dose. II: Performance. Alcohol Clin Exp Res. 2007;31(8):1365–1371.