Circadian variation in effects of ethanol in man

Twenty normal male volunteers received an intoxicating dose of oral ethanol (2 ml/kg vodka) and impairment of psychological functioning was documented over the succeeding 90 min. Half the subjects received ethanol at 0900 hr and half at 1800 hr. Those who received ethanol in the morning performed worse in tests of reaction time (p less than 0.002) and logical reasoning (p less than 0.002), even though blood alcohol levels were similar in the two groups. It is concluded that there is a circadian rhythm in the effects of ethanol in man.