A recent clinical trial conducted by Montreal’s McGill University and funded by the Canadian Automobile Association found that younger drivers were riskier to be on the road up to 5 hours after having smoked or vaped cannabis.
In this randomized study, participants completed tests in a sober state and then at 1, 3 and 5 hour increments after inhalation of a 100-mg dose of cannabis. They then measured performance in driving-simulation type tests and obtained self-reported perceptions as well.
There were 45 participants who completed all 180 tests. The results were interesting to say the least. Cannabis had absolutely no effect on “simple driving related tasks,” but, before hopping behind the wheel, read on. The effect on complex tasks was significant, as was the participants’ own perceptions that they weren’t able to drive as safely. Both of these effects lasted for around five hours.
During the driving simulation, “On no occasion did the no-cannabis state result in a greater risk of crash than the cannabis state, except on the task measuring vigilance, for which participants were twice as likely to be classified as highly vigilant at 1 hour after cannabis use.”
Before you go for a lifted cruise around the block though, keep the authors’ cautionary conclusion in mind:
“We found that among young recreational cannabis users, a regular dose of cannabis had no effect on simple and learned tasks, but its use led to significant impairments on complex and novel driving-related tasks, as well as perceived driving ability and safety, for up to 5 hours after use. The present finding that the first 5 hours after cannabis use affected driving-related performance substantiates the recommendations of Canada’s Lower-Risk Cannabis Use Guidelines, which recommend waiting 6 hours after cannabis use before driving.”