Study: Patients Show Few Changes in Driving Performance Following Marijuana Inhalation

Toronto, Canada: Patients who regularly use medical cannabis show little difference in their simulated driving performance following marijuana inhalation, according to data published in the April edition of the Journal of Concurrent Disorders.

A team of investigators from the University of Toronto, Health Canada, and the Centre for Addiction and Mental Health assessed the influence of cannabis on simulated driving performance among a group of daily medical cannabis consumers. Participants were asked to refrain from engaging in any cannabis use during the 48 hours immediately prior to the study sessions. Fourteen subjects completed the study.

Subjects performed on a driving simulator prior to and 30 minutes after inhaling cannabis. Three separate driving scenarios were programmed into the simulator.

Subjects decreased their overall mean speed following cannabis consumption. Cannabis smoking did not appear to influence subjects’ ability to maintain lateral control or their brake reaction time. Despite refraining from the use in cannabis in the days leading up to the study, subjects nonetheless possessed residual levels of THC (4ng/ml on average) in their blood prior to smoking marijuana during the study session.

Authors concluded: “The purpose of the present pilot study was to investigate the effects of therapeutic cannabis use on simulated driving. It was found that therapeutic cannabis reduced overall mean speed with no effects on straightaway mean speed, straightaway lateral control, or brake latency. … [F]urther investigation of the effects of therapeutic cannabis on driving are warranted.”

A prior literature review published in the journal of the German Medical Association concluded, “Patients who take cannabinoids at a constant dosage over an extensive period of time often develop tolerance to the impairment of psychomotor performance, so that they can drive vehicles safely.”

Full text of the study, “Effects of therapeutic cannabis on simulated driving: A pilot study,” appears in the Journal of Concurrent Disorders. Additional information is available in the NORML fact-sheet, ‘Marijuana and Psychomotor Performance.’