UNIVERSITY OF SASKATCHEWAN
Cannabis edibles pose major crash risk: USask study

The study, which concluded in 2025 with data currently unpublished, measured driving performance using a simulator that tracked reaction time, lane keeping, speed, and crash rates. Participants consumed 10 mg of cannabis with THC and were assessed before consumption and then at 1.5, 2.5, four, and six hours afterward. At the end of the assessment, the fare for a cab ride home was provided. 

"Edibles take a little bit longer to take effect compared to smoked or inhaled cannabis, so we were surprised to see that there were fairly immediate effects," said Dr. Alexander Crizzle (PhD), director of the Driving Research and Simulation Laboratory (DRSL) and professor in the USask School of Public Health. "[Impairment] remained quite significant even at 2.5 and four hours, and it did start to taper off at six hours but there were still effects of the cannabis in terms of their driving performance."  

Researchers noted that during the course of post-consumption, participants struggled with making quick decisions, such as reacting to pedestrians or vehicles cutting them off. 

"We also saw the ability to stay in your lane was impaired and, taking those all together, unsurprisingly, we saw a high number of crashes," said Crizzle. "Their movements are slower and the ability to make a decision is slower." 

Even four hours after consumption, more than 50 per cent of drivers still crashed on the simulator. Crizzle noted that there were no significant differences in performance based on age or gender. 

Driving after edibles? USask research shows high crash rates

Saskatchewan currently has a zero-tolerance policy for drugs and driving. Crizzle said the new evidence in this study funded by the Canadian Automobile Association (CAA), Mitacs, and Transport Canada reinforces that approach until more data is available. 

"Understanding the impacts on cannabis and driving is important given its association to fatal crashes. After alcohol, cannabis is a frequently detected substance in fatal crashes," said Crizzle. "This research is important, given the limited data currently available and helps educate the public on the risks related to driving, even in recreational cannabis users." 

The study was reviewed and approved by the USask Biomedical Research Ethics Board. Research at USask involving human participants is subject to ethical review under the Tri-Council Policy Statement (TCPS 2) to ensure participant safety, informed consent, and compliance with national research ethics policies.