How long should you wait to drive after toking? According to a new research study by McGill University, just one joint can harm your driving performance for more than five hours. In fact, when exposed to everyday road distractions, drivers who had consumed cannabis (a 100mg dose) experienced significant performance deterioration.
“The message is simple: If you consume, don’t drive. Find another way home or stay where you are,” Jeff Walker, chief strategy officer for the Canadian Automobile Association (CAA), told the Montreal Gazette.
The study tested the driving abilities of 18 to 24 year olds who identified themselves as occasional cannabis consumers (individuals who had consumed at least once in the last three months but not more than four times weekly). Using a driving simulator, the study tested 45 individuals—24 men and 21 women—to see how they drove after a 100mg dose of cannabis.
The test subjects consumed flower with “the average THC levels in street-grade cannabis” via a vaporizer. The goal was to replicate the effects of smoking a single joint. Then, once high, researchers tested driving performance at intervals up to five hours, comparing the results to their baseline driving sans cannabis.
The results were interesting, to say the least.
Without distractions on the road, divers performed the same whether high or not. However, when common roadside distractions were added—such as driving through a busy intersection—performance deteriorated rapidly with cannabis.
“When we added distractions and tasks [that] required more attention and more focus and cognitive skills like divided attention … response time was much greater,” study co-author Dr. Tatiana Ogourtsova said. “I think the five hours maybe came as a surprise. We thought maybe the effects would not be as strong. But they were very significant.”
The study, conducted by the Research Institute of the McGill University Health Centre and McGill University and funded by the Canadian Automobile Association, was the first of its kind to use driving simulators to record performance after cannabis consumption. Other studies had previously revealed that high drivers had slower braking and reaction times, impaired lane positioning, and increased caution, but this was the first study to determine safety levels hours after usage based on performance.
What they found was that even five hours after use, drivers did not perceive themselves as safe to drive, and they weren’t. Not only did all drivers present slower driving times, but they also couldn’t handle novel tasks that they hadn’t experienced before.
This is a huge problem considering that one in seven Canadian cannabis users (14 percent) reported driving two hours after using (Statistics Canada). In addition, 1.4 million Canadians admitted to being a passenger in a vehicle driven by someone who had smoked in the last two hours.
To keep the roads safe, Canada has implemented some fairly strict guidelines for driving under the influence. Those caught with cannabis in their system could lose their license, face stiff fines and end up with a criminal record. In fact, in Quebec, the penalties are the same as for drunk driving. If you’re suspected of driving while high, police can arrest you and force you to provide a urine sample for analysis.