Behavioral effects of oral versus intravenous administration of diazepam

The behavioral effects of oral versus intravenous administration of diazepam were studied in 50 volunteers using a battery of memory, cognitive, mood and psychomotor tests repeated over a 4.5 hr period. Subjects received diazepam 0.2 mg/kg or placebo as capsules, commercial tablets or intravenous solution in a randomized double blind manner. While a quick onset of effects occurred with intravenous administration followed by the capsule and tablet oral administrations in that order, the recovery rate was similar for the 3 methods of administration. Contrary to many claims in the literature the effects of oral administration were substantial. Behavioral impairment was directly related to the magnitude of the memory component of the task. On many of the tasks the pattern of diazepam impairment was one of delayed improvement of performance, a pattern which would only be apparent with repeated testing. Subjects who received diazepam showed a paradoxical enhancement of recall for material learned before the drug.