Abstract

In a residential hospital research ward setting, the effects of and preference for placebo, oxazepam (480 mg) and diazepam (40, 80 and 160 mg) were studied in human volunteers with histories of sedative drug abuse. Doses p.o. were administered every 3rd day under double-blind conditions. After an initial exposure to the letter-coded test drugs, a series of choice days was scheduled on which subjects chose between two available drug alternatives. Compared with oxazepam, diazepam produced greater liking (area under the time-action curve), peak liking and euphoria and was judged to be of greater monetary street value. Diazepam was categorized as producing barbiturate-like subjective effects more frequently than was oxazepam (54 vs. 21%), whereas oxazepam was identified as placebo more often than diazepam (32 vs. 4%). Diazepam was associated with a more rapid onset of effect than was oxazepam, and this rapid onset was repeatedly cited by subjects in poststudy written comments as being a desirable feature of the drug effect. In choice tests, 80 and 160 mg of diazepam were preferred to 480 mg of oxazepam on 62.5 and 91.7% of the choice tests, respectively. In choice tests between placebo and drug, placebo was never preferred to diazepam; however, placebo was preferred to oxazepam on 21.4% of choice tests. Overall, these results extend previous experimental observations suggesting that diazepam has a higher abuse liability than oxazepam. The results are also compatible with an analysis of epidemiological data showing that diazepam abuse uniformly exceeds oxazepam abuse on seven epidemiological measures of drug abuse.