The effect of zopiclone 7.5 mg on the sleep, mood and performance of shift workers.

Shift workers often complain of an inability to sleep well between successive periods of work. The purpose of the study was to assess the influence of zopiclone, hypnotic with minimal residual effects, on work-time performance and mood. In this double-blind, cross-over study, 12 healthy male volunteers, aged between 18 and 35 years, from the Royal Air Force, working 12 h shifts in radar installations, were given zopiclone 7.5 mg at bed time or placebo for 2 shift cycles in a randomized order. Zopiclone significantly improved night time sleep, with a trend towards improvement of day-time sleep. There was no effect on psychomotor performance (assessed by critical flicker fusion threshold, choice reaction time and digit symbol substitution test) nor on mood (assessed by visual analogue scales). It can be concluded that zopiclone is a safe hypnotic which can be used by shift workers without impairing work time performance.