Youth who maintained consistently high cannabis use or increased their use from adolescence to young adulthood were more likely to engage in impaired driving compared to occasional users, decreasers, or abstainers.
Parents, young adults, policymakers, and public health officials focused on cannabis and driving safety.
10-year follow-up across 6 time points
What the researchers found
Chronic cannabis users and those with increasing use patterns were more likely to engage in risky impaired driving behaviors. Frequency of cannabis use independently predicted impaired driving risk after controlling for age, sex, socioeconomic status, other substance use, and simultaneous substance use. Youth using cannabis more than once a week were also more likely to drink heavily and use alcohol simultaneously.
Why it matters
With cannabis legalization expanding, understanding which usage patterns predict driving risk can help target prevention efforts toward the highest-risk groups.
The numbers in context
10-year follow-up period (2003-2013). 6 biennial interviews. 5 user groups identified: chronic users, increasers, occasional users, decreasers, and abstainers. Cannabis use more than once a week associated with increased driving risk.
How the study worked
Longitudinal Victoria Healthy Youth Survey following youth biennially over 6 occasions across 10 years (2003-2013), examining the association between marijuana use trajectories and impaired driving risks.
What this study cannot tell us
Self-reported data. Single Canadian city (Victoria). Driving risk was self-reported, not measured through accident records or driving performance tests.
How to read the evidence
Longitudinal design with multiple time points strengthens causal inference, though self-reported outcomes limit certainty.
When this study was published
2019 study using data collected from 2003 to 2013.
The bigger picture
This study moves beyond cross-sectional snapshots to show that the trajectory of cannabis use matters for driving risk, not just whether someone uses at a single point in time.
Questions still open
- Would targeted interventions for "increasers" during adolescence prevent later impaired driving? How do these patterns interact with cannabis potency changes over time?
Common questions
Does cannabis use in teens predict impaired driving later?
Is occasional cannabis use linked to driving risk?
Read the original research
Marijuana trajectories and associations with driving risk behaviors in Canadian youth.
Traffic injury prevention, 20(5), 472-477
Citation
Sukhawathanakul, Paweena; Thompson, Kara; Brubacher, Jeff; Leadbeater, Bonnie. (2019). Marijuana trajectories and associations with driving risk behaviors in Canadian youth.. Traffic injury prevention, 20(5), 472-477. https://doi.org/10.1080/15389588.2019.1622097