Toronto, ON (August 31, 2026) – A first-of-its-kind trial led by researchers of the Driving Simulation Laboratory at the Centre for Addiction and Mental Health (CAMH), published today in JAMA Network Open, has found that commercially available cannabis edibles significantly impair driving performance on a simulator in a dose-dependent manner, even when blood THC levels remained below the legal thresholds used to detect cannabis-impaired driving.
“Our findings suggest that edible cannabis can significantly impair driving performance even when blood THC concentrations are within legal limits," says Dr. Bernard Le Foll, Senior Scientist at the Institute for Mental Health Policy Research (IMHPR) and the study's first author. “As edible cannabis products become increasingly popular, it's important that both consumers and policymakers understand that blood THC levels may not fully reflect a person's level of impairment.”
Cannabis edibles have become increasingly popular in Canada. Of the quarter of Canadians who use cannabis for non-medical purposes, more than half consume edibles, making them the second most popular cannabis product. Previous studies have shown that cannabis negatively affects driving performance, but most have only examined the effects of smoked or inhaled cannabis. Very few studies have assessed the effects of edibles on driving, even though it is well known that oral THC administration leads to lower blood THC concentrations, raising concerns that drivers may experience meaningful impairment while remaining below the blood THC thresholds commonly used in roadside enforcement.
Addressing a Growing Knowledge Gap
To determine the effects of edibles on driving, the team conducted a double-blind, placebo-controlled randomized trial involving 40 adults aged 19 to 45 who regularly used cannabis and consumed edibles at least monthly. Participants either received placebo, 2 mg, 10 mg or 20 mg doses of THC (the active compound in cannabis responsible for the high users experience) in edible form, and their driving performance was assessed on a simulator two, five and 24 hours after consumption.
The results showed a clear dose-dependent effect on driving performance two and five hours after consumption. Compared with placebo, participants who consumed 10 mg or 20 mg of THC had significantly greater difficulty maintaining lane position, a well-established measure of driving impairment. Reaction times were also slower after THC consumption, and participants reported being less willing to drive and less confident in their driving ability as THC doses increased.
The doses examined in the study reflect amounts that consumers may encounter in practice. Ten milligrams of THC is the maximum amount allowed in a single package of legal cannabis edibles in Canada; however, many regular cannabis users will often consume multiple products, resulting in substantially higher THC intake.
The Disconnect Between Blood THC Levels and Impairment
Importantly, the study found a clear disconnect between driving impairment and blood THC levels. All peak blood THC concentrations, even those among participants who consumed the highest dose of THC, were below or near common per se thresholds used for roadside enforcement.
The findings are especially striking when compared with previous CAMH research on the effects of smoked cannabis on driving. Although the current study found that the highest edible dose produced a similar degree of driving impairment as high-potency smoked cannabis, peak blood THC concentrations were nearly ten times lower.
“Many people may underestimate the impairment caused by cannabis edibles,” says Dr. Christine Wickens, Senior Scientist at IMHPR and co-author of the study. “Our findings show that commonly consumed doses can significantly affect critical driving skills, reinforcing the need for caution when making decisions about driving after use.”
“What this study makes clear is that the relationship between THC in the bloodstream and actual driving impairment is complex. Continued research is essential to better understand the risks associated with emerging cannabis products and to support effective approaches to road safety,” adds Dr. Bruna Brands, Collaborative Scientist at IMHPR and senior author of the study.
Funding for this study was obtained from Public Safety Canada by Drs. Bruna Brands and Bernard Le Foll.
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About the Centre for Addiction and Mental Health (CAMH)
The Centre for Addiction and Mental Health (CAMH) is Canada's largest mental health and addiction teaching hospital and a world leading research centre in this field. CAMH combines clinical care, research, education, policy development and health promotion to help transform the lives of people affected by mental illness and addiction. CAMH is fully affiliated with the University of Toronto and is a Pan American Health Organization/World Health Organization Collaborating Centre. For more information, please visit camh.ca or follow @CAMHnews on Bluesky and LinkedIn.