Effects of diazepam on cerebral metabolism and mood in normal volunteers

The effects of diazepam on regional cerebral metabolism were examined in eight healthy volunteers using positron emission tomography with 18-fluorodeoxyglucose as the tracer. Each subject was tested three times, at 1-week intervals, with placebo, a low oral dose of diazepam (0.07 mg/kg), and a moderate dose of diazepam (0.14 mg/kg). Subjects completed mood questionnaires before and at regular intervals after taking the drug, and performed a vigilance task during the 60-minute period of tracer uptake. The effects of the drug on cerebral metabolism were examined alone and in relation to the subjective and behavioral effects of the drug. Both doses of diazepam decreased global (whole brain) metabolic rate but did not affect specific regions differentially. Subjects experienced sedative like effects during all three scans (placebo as well as drug). Compared to placebo, both doses of diazepam decreased anxiety, and neither dose produced significant impairment of task performance. Neither the subjective nor behavioral drug effects were correlated with the changes in metabolic rate. Thus, diazepam decreased whole brain metabolic rate at doses that produced only modest subjective or behavioral effects. The changes in metabolic rate were not clearly related to other observable drug effects.