Effects of lorazepam administration on striatal dopamine D2 receptor binding characteristics in man--a positron emission tomography study.

Lorazepam is a widely used benzodiazepine class anxiolytic drug. It is known to enhance GABAergic neurotransmission in the brain, but the actions of benzodiazepines on other neurotransmitter systems are largely unknown. We studied the effects of 1 week's administration with lorazepam (2 mg daily, PO) or placebo on striatal D2 dopamine receptors in four healthy male volunteers using a double-blind randomized cross-over design. D2 receptor density and affinity as well as binding potential (Bmax/Kd) were measured with [11C]-raclopride and positron emission tomography. Although the individual responses varied, lorazepam did not significantly affect D2 receptor binding characteristics, nor did the average effect sizes exceed test-retest variability of the method. In conclusion, the results suggest that striatal D2 dopamine receptor characteristics are not affected by the clinically relevant lorazepam treatment regimen used.