Cannabis may impair driving ability for up to 4 hours, study finds

Traffic Safety Corner

(Via Fox News) Cannabis can impair a person’s ability to drive up to 4 hours after the drug is used, according to a recent study. According to the report, recovery was not fully seen until 4.5 hours post smoking.

A group of researchers from the Center for Medicinal Cannabis Research at the University of California San Diego looked at 191 regular cannabis users and found that smoking cannabis led to significantly declined simulated driving scores, according to the authors of the two-year randomized trial study. A lit joint of cannabis being held in hand, hand is also on steering wheel of a car. Outside of the window is a blurred road.

The participants were given either a placebo cigarette or a cannabis cigarette containing either 5.9 % or 13.4 % levels of delta-9-tetrahydrocannabinol (THC), the psychoactive compound in cannabis, the study said.

The researchers found participants in the THC group showed a significant decline in Composite Drive Scores (CDS) related to a 25-minute simulated driving experience. The CDS assessed driving variables that included following a lead car while varying speeds, noting swerving in their lane, and responding to divided attention tasks, according to the study.

The sharpest comparative difference in driving scores between the placebo and the THC group was noted at 30 minutes and 1 hour and 30 minutes after the time of inhaling the cannabis cigarette, according to the published report.

The study said borderline differences in driving scores were found between the two groups at 3 hours 30 minutes and no differences were noted at 4 hours 30 minutes.

The California researchers said that the study emphasizes the challenge in understanding the relationship between cannabis consumption and an individual’s ability to drive as well as identifying which individuals are most at risk for impaired driving when using cannabis.

Co-author of the study Igor Grant, MD, CMCR director and Distinguished Professor of Psychiatry at UC San Diego School of Medicine pointed out in the release the need to appropriately label cannabinoid medicines.

The study authors suggested future research addressing factors such as personal experience with cannabis, ways cannabis is ingested by an individual, and the individual’s biological differences in relation to driving impairment.

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Read the full study: Driving Performance and Cannabis Users’ Perception of Safety