Quantitative effects of cetirizine and diphenhydramine on mental performance measured using an automobile driving simulator.

The purpose of this study was to assess the effects of cetirizine on objective measures of mental performance. Fifteen subjects were given single doses of cetirizine (20 mg, 10 mg, and 5 mg) diphenhydramine, 50 mg (positive control), and placebo (negative control) in this randomized, double-blinded, crossover study. An automobile driving simulator, digit symbol substitution, Trails B maze tracking and subjective feelings of drowsiness were measured at 0, 2, 4, 6, 8, and 24 hours after the dose. No differences between placebo and any of the three doses of cetirizine could be detected, however, diphenhydramine produced impaired mental performance and drowsiness. These data indicate that these doses of cetirizine produce little or no effect on cognitive function or mental performance.