Effects of oral contraceptives on diazepam-induced psychomotor impairment.

Eight young women taking oral contraceptives and 10 young men each received three different doses of diazepam, 0.07, 0.14, and 0.28 mg/kg. The women also received each dose both on days 10 and 28 of an oral contraceptive cycle. Performance based on both a psychomotor and cognitive-encoding task was significantly impaired after a 0.28-mg/kg dose of diazepam in women taking oral contraceptives and in men. In general, however, impairment in performance was less on day 10 than on day 28 of the oral contraceptive cycle. The onset of behavioral impairment was also slower on cycle day 10 than on day 28; peak impairment was reached at 20 min after dosing for men and women on day 28, but at 60 min for women on day 10. The cycle phase effects are potentially dangerous because of their unexpected nature. Individuals may obtain an expectation of intoxication based on the 21-day OC period yet experience capriciously greater acute impairment during their 7-day menstrual pause.