Study: Medical Cannabis Patients Show Little Change In Driving Performance After Use

A group of patients who regularly use medical marijuana showed little difference in driving performance after inhaling cannabis, according to the findings of a Canadian study released recently. Results of the study by researchers from the University of Toronto, Health Canada, and the Centre for Addiction and Mental Health were published last month in the Journal of Concurrent Disorders.

To conduct the study, investigators assessed the effect that cannabis use has on the simulated driving performance of a group of 14 daily marijuana users. All participants had a medical recommendation to use medical marijuana for an underlying condition and reported that they did so on a daily basis. Subjects were asked to refrain from using cannabis for the 48 hours prior to their participation in the research, although they still had residual blood levels of THC that averaged four nanograms per milliliter prior to using cannabis on the day of the study.

The researchers programmed three different scenarios into the driving simulator to be completed by the participants in the study. Several indicators of driving performance such as speed, the ability to maintain lateral control, and braking were measured during the driving simulations. The study’s subjects were asked to complete the simulations prior to inhaling cannabis and again 30 minutes after.

Following their use of marijuana, the study subjects reduced their mean driving speed. Smoking cannabis did not appear to affect their braking reaction time or their ability to maintain lateral control while driving.

“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,” the researchers wrote.

“Further investigation of the effects of therapeutic cannabis on driving are warranted,” they added.

Other Studies on Cannabis and Driving

The study’s authors also noted that while previous studies of cannabis use and driving had shown drivers showed a greater tendency to weave back and forth on the roadway, the drivers they studied did not seem to exhibit the same effect.

“It should be mentioned that, in the present study, therapeutic users of cannabis did not demonstrate changes in lateral control after smoking therapeutic cannabis,” they wrote.

Although some studies have shown that cannabis use may have a detrimental effect on driving performance, a review of existing literature published in the journal of the German Medical Association in 2012 found that habitual marijuana users may be able to avoid impairment.

“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,” the report reads.