Cognition and motor control as a function of Delta(9)-THC concentration in serum and oral fluid: Limits of impairment.
Cannabis use has been associated with increased risk of becoming involved in traffic accidents; however, the relation between THC concentration and driver impairment is relatively obscure. The present study was designed to define performance impairment as a function of THC in serum and oral fluid in order to provide a scientific framework to the development of per se limits for driving under the influence of cannabis. Twenty recreational users of cannabis participated in a double-blind, placebo-controlled, three-way cross-over study. Subjects were administered single doses of 0, 250 and 500mug/kg THC by smoking. Performance tests measuring skills related to driving were conducted at regular intervals between 15min and 6h post smoking and included measures of perceptual-motor control (Critical tracking task), motor impulsivity (Stop signal task) and cognitive function (Tower of London). Blood and oral fluid were collected throughout testing. Results showed a strong and linear relation between THC in serum and oral fluid. Linear relations between magnitude of performance impairment and THC in oral fluid and serum, however, were low. A more promising way to define threshold levels of impairment was found by comparing the proportion of observations showing impairment or no impairment as a function of THC concentration. The proportion of observations showing impairment progressively increased as a function of serum THC in every task. Binomial tests showed an initial and significant shift toward impairment in the Critical tracking task for serum THC concentrations between 2 and 5ng/ml. At concentrations between 5 and 10ng/ml approximately 75-90% of the observations were indicative of significant impairment in every performance test. At THC concentrations >30ng/ml the proportion of observations indicative of significant impairment increased to a full 100% in every performance tests. It is concluded that serum THC concentrations between 2 and 5ng/ml establish the lower and upper range of a THC limit for impairment.[1]References
- Cognition and motor control as a function of Delta(9)-THC concentration in serum and oral fluid: Limits of impairment. Ramaekers, J.G., Moeller, M.R., van Ruitenbeek, P., Theunissen, E.L., Schneider, E., Kauert, G. Drug and alcohol dependence. (2006) [Pubmed]
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