Lack of sedative and cognitive effects of diphenhydramine and cyclobenzaprine in elderly volunteers

A double-blind, in-clinic, placebo-controlled, randomized, three-period crossover study was undertaken to investigate the potential sedative and cognitive effects of diphenhydramine 50 mg, p.o. and cyclobenzaprine 5 mg, p.o. in elderly volunteers. Subjects were given 10 doses of each treatment over a 4-day period according to a t.i.d. schedule. A battery of cognitive tests was administered 2 h after the first and last dose of each treatment period and subjects also completed visual analogue scale subjective ratings at regular intervals. There was no evidence that either drug caused drowsiness or affected cognitive test performance. These findings contrast with previous data using similar assessments in young volunteers, which indicated clear diphenhydramine- induced impairments. Contrary to commonly held belief, the elderly appear to be less sensitive than the young to the central nervous system effects of oral diphenhydramine.