Effects of alprazolam and diazepam on the daytime sleepiness of non-anxious subjects.

Eighteen non-anxious volunteers underwent sleep recordings and daytime tests of sleepiness, performance, and mood while receiving, either alprazolam 0.5 mg b.i.d. or diazepam 5 mg b.i.d. for 7 consecutive days. Recordings and tests were done before treatment and on the 1st and 7th days of treatment. Nocturnal sleep changes were similar for both groups; there were no statistically significant changes in mood. However, levels of daytime sleepiness differed. Alprazolam subjects showed more daytime sedation than diazepam subjects on treatment day 1, but showed a significant decrease in Day 1-7 daytime sedation. Although diazepam subjects were less sedated at the onset, they showed no tolerance to this effect; thus by treatment day 7, the two groups did not differ in levels of daytime sleepiness. Results suggested that tolerance to alprazolam's sedative effects (which develops during the 1st week of treatment) may be separable from tolerance to its antianxiety effects (which develops after at least 4 weeks). As daytime sedation is common and potentially dangerous with most anxiolytics, selective tolerance to this side effect is highly desirable.