University of Toronto Researchers Uncover Potency's Role in Cannabis Driving Risks

Canadian universities continue to lead vital public health investigations into cannabis use, with a new study from the University of Toronto and the Centre for Addiction and Mental Health (CAMH) revealing that higher tetrahydrocannabinol (THC) potency in smoked cannabis markedly impairs driving performance. Published in Scientific Reports, this research highlights how products with elevated THC levels—now commonplace in the legal market—lead to greater deviations in lane position, increased speed variability, and slower reaction times on simulated roads. As cannabis consumption evolves post-legalization, such findings from U of T experts emphasize the need for heightened awareness among drivers and ongoing education in pharmacy and public health programs across Canadian colleges and universities.

The study's implications extend beyond individual safety, informing road safety policies and training curricula at institutions like U of T's Leslie Dan Faculty of Pharmacy. With THC concentrations in commercial cannabis surging from around 4 percent in the mid-1990s to averages exceeding 14 percent by 2019 and some products nearing 30 percent today, understanding these potency-driven effects is crucial for fostering safer communities.

Cannabis Legalization in Canada: A Context of Rising Potency and Use

Since recreational cannabis legalization in October 2018, Canada has witnessed transformative shifts in consumption patterns and product availability. Legal sales have diversified, with dried flower, vapes, edibles, and concentrates dominating the market. Health Canada's Canadian Cannabis Survey from 2024 indicates that 26 percent of Canadians aged 16 and older reported past-year non-medical use, up from 22 percent pre-legalization. Notably, 35 percent of users prefer higher-THC, lower-cannabidiol (CBD) products, reflecting a market tilt toward potent options.

This potency escalation poses unique road safety challenges. While overall impaired driving reports after cannabis use have declined slightly to 18 percent among consumers in 2024 (from 27 percent in 2018), 16 percent still drive within two hours of smoking or vaping. Universities like the University of Toronto are at the forefront, bridging gaps in evidence to guide safer behaviors amid these trends.

Behind the Scenes: U of T and CAMH's Driving Simulator Methodology

The CAMH Driving Simulation Laboratory, affiliated with the University of Toronto, employs a state-of-the-art multi-screen simulator mimicking real-world conditions, complete with a driver's seat, steering wheel, pedals, and dashboard from a General Motors vehicle. This setup allows precise measurement of psychomotor skills without real-road dangers.

In this randomized, double-blind, placebo-controlled trial (NCT03656029), 40 regular cannabis users aged 19-45 with valid licenses participated. Each smoked a 750 mg joint ad libitum under four conditions: placebo (<0.1 percent THC, 0.75 mg), low potency (6.25 percent THC, 47 mg), medium (12.5 percent, 94 mg), or high (22 percent, 165 mg). Performance was assessed pre-smoking and at 30 and 90 minutes post, via single- and dual-task drives. Blood THC levels were monitored, and subjective intoxication rated.

Key Findings: Dose-Dependent Impairments from THC Potency

Results demonstrated clear potency gradients. Mean speed remained stable, but maximum speed rose significantly under medium (p=0.006) and high (p=0.02) conditions versus placebo. Standard deviation of lateral position (SDLP)—a weaving measure—increased across all THC doses (p<0.001), indicating poorer lane control. Reaction time (RT) lengthened notably for medium and high potencies (p<0.001).

• Higher blood THC correlated positively with SDLP (p<0.001) and RT (p=0.023).
• Subjective reports: Participants felt poorer driving ability and less willing to drive at elevated potencies.
• Effects persisted similarly at 30 and 90 minutes, suggesting short waits insufficient.

These metrics align with real-world collision risks, where lane deviations and delayed responses contribute to accidents. The full study is available here.

Blood THC Levels: Linking Lab Data to Real-World Detection Challenges

Blood THC peaked higher with potency, reinforcing simulator impairments. While Canada's zero-tolerance for THC over 2-5 ng/mL aids enforcement, residual levels in chronic users complicate per se laws. U of T researchers note that potency influences peak concentrations and duration, urging time-based abstinence alongside testing.

Post-legalization data shows THC-positive drivers rising (e.g., British Columbia roadside surveys), though fatal crashes link more to high levels (>5 ng/mL). CAMH's work informs nuanced policies balancing use freedom and safety.

Aligning with Canada's Lower-Risk Cannabis Use Guidelines

The findings bolster Canada's Lower-Risk Cannabis Use Guidelines, recommending at least six hours post-use before driving—evidence-based on impairment subsidence timelines varying by dose, method, and user tolerance. U of T's evidence shows even 90 minutes inadequate for high-potency smoked cannabis, supporting conservative waits.

More details on the guidelines can be found here, emphasizing individual factors like edibles' longer onset.

Canadian Universities Driving Cannabis Road Safety Research

U of T and CAMH pioneer alongside peers: University of Saskatchewan's 2025 edibles study found 75 percent of young users crashed in simulators post-edibles; University of British Columbia research indicates low-THC (<2.5 percent) poses minimal risk; McGill University explores youth crash vulnerabilities up to five hours post-use.

These efforts, funded by CIHR, position Canadian higher education as global leaders in translational science, training future pharmacists and public health experts at faculties like U of T's Leslie Dan.

Post-Legalization Trends: Impaired Driving Stats and Policy Responses

Despite awareness gains (86 percent recognize cannabis impairs driving per 2024 CCS), challenges persist. THC-positive fatally injured drivers rose post-2018, though overall collisions show mixed trends—up in some provinces, stable others. Public Safety Canada 2024 data: 10.4 percent of young drivers (16-19) test cannabis-positive roadside.

Policies evolve: Oral fluid screening (2 ng/mL THC), zero-tolerance for novices. Universities advocate education; U of T's research aids MADD Canada and CAA campaigns.

Explore CCS data here.

Higher Education's Role: Preparing Students for Cannabis Realities

Canadian pharmacy programs, including U of T's, integrate cannabis pharmacotherapy, impairment counseling, and policy. With mandatory education in Ontario, curricula cover potency risks, drug interactions, and patient advising—vital as pharmacists recommend lower-risk use.

Public health degrees at U of T's Dalla Lana School emphasize epidemiology, simulator tech, and interventions. Community colleges offer road safety certifications incorporating cannabis modules, ensuring graduates address this public health priority.

Stakeholder Perspectives: From Experts to Everyday Canadians

Beth Sproule notes, “The increasing use of cannabis... paired with higher potency... means it is really important to understand how cannabis use affects driving.” Justin Matheson adds, “Driving is a complex behaviour requiring coordinated cognitive and psychomotor skills.”

Stakeholders like CAA highlight edibles' risks; police stress detection tech. Surveys show 79 percent of consumers acknowledge impairment, yet gaps remain in potency awareness.

Future Directions: Edibles, Gender, and Chronic Use Research

U of T plans edibles studies (delayed onset, prolonged effects) and gender analyses, as women metabolize THC differently. Chronic vs. occasional user differences need exploration, alongside multi-substance combos.

Canadian universities gear for AI-enhanced simulators, real-road validations, informing federal reviews by 2026.

Photo by Elsa Olofsson on Unsplash

Actionable Insights for Safer Roads and Informed Communities

Key takeaways: Plan ahead—wait 6+ hours post-use; choose lower-potency; avoid edibles before drives. Universities promote via campaigns, workshops. As research hubs, they equip professionals to mitigate risks, ensuring cannabis benefits outweigh harms in a legalized landscape.