Effects of terfenadine, diphenhydramine, and placebo on skills performance.

The behavioral effects of the antihistamines terfenadine and diphenhydramine were compared in a placebo-controlled, double-blind crossover study. Performance of skills deemed important in safe man-machine interactions was objectively assessed one, three, and five hours after administration of test substances. The results indicate that diphenhydramine use resulted in various degrees of impairment of the ability to perform a visual-search task, a tracking task, a divided-attention task, and a vigilance task. Terfenadine users performed as well as or better than placebo-treated subjects. No differences between terfenadine and placebo were found on a subjective evaluation scale. Diphenhydramine users consistently reported feelings of impairment.