Discriminative stimulus properties of low doses of ethanol in humans

Discriminative stimulus properties of low doses of ethanol were evaluated in humans using established behavioural drug discrimination procedures. Twenty-five moderate drinkers (12 females and 13 males) were trained to discriminate placebo from 0.2 g/kg ethanol in 200 ml tonic water mixed with Tabasco sauce and drunk in portions of 50 ml every 15 s. Seventeen of the subjects (ten females and seven males) were able to reach criterion performance (at least 80% correct responses). Generalisation responding across ethanol doses of 0 (placebo), 0.025, 0.05, 0.1 and 0.2 g/kg was examined the day after training using a procedure in which subjects reported the extent to which the test stimulus resembled the training dose. At the end of each generalisation session, self ratings of mood changes, physiological responses and performance in a working memory and a time estimation task were evaluated. Subjects were able to distinguish the three higher doses of ethanol from placebo. Self ratings indicated that subjects' ability to distinguish ethanol from placebo was related, at the highest dose, to change of taste, but to feelings of light-headedness at the lower doses. Ethanol administration influenced skin conductance measurements but there was no relationship found between changes in skin conductance and the ethanol discriminative stimulus. These data suggest a difference in the nature of the discriminative stimulus of ethanol between high (training) and low (generalising) doses as indicated in the subjective reports.