Public Health and Safety

Driving After Marijuana Use? – Impairment Can Last For Hours

“I’m okay to drive.” But, in reality are you and how do you know for sure?

A new report in JAMA Psychiatry (January 26, 2022) examines a person self-perception of feeling high after using marijuana. Authors Marcotte (et.al.) point out that the impairment felt after using marijuana can last for hours, even well after when a person thinks they are safe to drive.

Clinical trials were conducted from 2017 – 2019 using marijuana of three (3) levels of THC potency, 13.4%, 5.9% and .02% (placebo). A driving simulator was also used to monitor effects to driving behavior. The participants (n=199) were divided into three (3) group by potency strains and were instructed to smoke the same way you would at home to get high.  When observing the driving behavior of the two (2) THC groups against the placebo group, the THC group “had a significant decline” in the driving abilities. The decline was most notable as soon as 30 minutes – 90 minutes. It was not until nearly 4 hours later when there was no significant  difference between the group. 

As to the participants subjective perception of their own state of impairment after use, a majority (nearly 70%) felt they were safe to drive after 90 minutes. This despite the fact there was no objective improvement in driving performance at that same point in time. The most favorable results in driving performance were seen at 4.5 hours after last use.

Read Time: 10 minutes

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