Cognition and motor control as a function of Delta9-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 500 microg/kg THC by smoking. Performance tests measuring skills related to driving were conducted at regular intervals between 15 min 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 5 ng/ml. At concentrations between 5 and 10 ng/ml approximately 75-90% of the observations were indicative of significant impairment in every performance test. At THC concentrations >30 ng/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 5 ng/ml establish the lower and upper range of a THC limit for impairment.
Ramaekers
J G
JG
Experimental Psychopharmacology Unit, Department of Neurocognition, Faculty of Psychology, Maastricht University, 6200 MD Maastricht, The Netherlands. j.ramaekers@psychology.unimaas.nl
Moeller
M R
MR
van Ruitenbeek
P
P
Theunissen
E L
EL
Schneider
E
E
Kauert
G
G
D000328:Adult; D001334:Automobile Driving / Q000523:psychology; D003071:Cognition / Q000187:drug effects*; D018592:Cross-Over Studies; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D013759:Dronabinol / Q000009:adverse effects / Q000097:blood*; D005260:Female; D006801:Humans; D007175:Impulsive Behavior / Q000097:blood / Q000139:chemically induced / Q000523:psychology; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects / Q000097:blood* / Q000523:psychology; D008657:Metabolic Clearance Rate / Q000502:physiology; D011597:Psychomotor Performance / Q000187:drug effects*; D011698:Pursuit, Smooth / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects; D012307:Risk Factors; D012463:Saliva / Q000378:metabolism
D013759:Dronabinol