Individual differences in the biphasic effects of ethanol

Ethanol exerts both stimulant-like and sedative-like subjective and behavioral effects in humans depending on the dose, the time after ingestion and, we will argue, also on the individual taking the drug. This study assessed stimulant-like and sedative-like subjective and behavioral effects of ethanol during the ascending and descending limbs of the blood alcohol curve across a range of doses in nonproblem social drinkers. Forty-nine healthy men and women, 21 to 35 years old, consumed a beverage containing placebo or ethanol (0.2, 0.4, or 0.8 g/kg) on four separate laboratory sessions, in randomized order and under double-blind conditions. Subjective and behavioral responses were assessed before and at regular intervals for 3 hr after ingestion of the beverage. The lowest dose of ethanol (0.2 g/kg) only produced negligible subjective effects compared to placebo. The moderate dose (0.4 g/kg) increased sedative-like effects 90 min after ethanol ingestion but did not increase ratings of stimulant effects at any time. The highest dose (0.8 g/kg) increased ratings of both stimulant- and sedative-like effects during the ascending limb and produced only sedative-like effects during the descending limb. Closer examination of the data revealed that individual differences in response to the highest dose of ethanol accounted for this unexpected pattern of results: about half of the subjects reported stimulant-like effects on the ascending limb and sedative-like effects on the descending limb after 0.8 g/kg ethanol, whereas the other half did not report stimulant-like effects at any time after administration of ethanol. These results challenge the simple assumption that ethanol has biphasic subjective effects across both dose and time, and extend previous findings demonstrating individual differences in response to ethanol.