Effect of γ-hydroxybutyrate (GHB) on driving as measured by a driving simulator

RationaleGamma-hydroxybutyrate acid (GHB), a GABAB receptor agonist approved for treatment of narcolepsy, impairs driving ability, but little is known about doses and plasma concentrations associated with impairment and time course of recovery.ObjectiveTo assess effects of oral GHB (Xyrem®) upon driving as measured by a driving simulator, and to determine plasma concentrations associated with impairment and the time course of recovery.MethodsRandomized, double-blind, two-arm crossover study, during which 16 participants received GHB 50mg/kg orally or placebo. GHB blood samples were collected prior to and at 1, 3, and 6h post dosing. Driving simulator sessions occurred immediately after blood sampling.ResultsPlasma GHB was not detectable at baseline or 6h post dosing. Median GHB concentrations at 1 and 3h were 83.1mg/L (range 54-110) and 24.4mg/L (range 7.2-49.7), respectively. Compared to placebo, at 1h post GHB dosing, significant differences were seen for the life-threatening outcome collisions (p < 0.001) and off-road accidents (p = 0.018). Although driving was not faster, there was significantly more weaving and erratic driving with GHB as measured by speed deviation (p = 0.002) and lane position deviation (p = 0.004). No significant impairment regarding driving outcomes was found in the GHB group at 3 and 6h post dose.ConclusionGHB in doses used to treat narcolepsy resulted in severe driving impairment at 1h post dosing. After 3 to 6h, there was full recovery indicating that safe driving is expected the next morning after bedtime therapeutic GHB use in the absence of other substances.