Cannabis and traffic collision risk: findings from a case-crossover study of injured drivers presenting to emergency departments

Int J Public Health. 2014 Apr;59(2):395-404. doi: 10.1007/s00038-013-0512-z. Epub 2013 Sep 24.


Objectives: This study examined whether acute cannabis use leads to an increased collision risk.

Methods: Participants were 860 drivers presenting to emergency departments in Toronto and Halifax, Canada, with an injury from a traffic collision, between April 2009 and July 2011. Cannabis and other drug use were identified either through blood sample or self-report. A case-crossover design was employed with two control conditions: a fixed condition measuring substance use during last time driving, and whether the driver typically uses cannabis prior to driving. Collision risk was assessed through conditional fixed-effects logistic regression models.

Results: Results revealed that 98 (11 %; 95 % CI: 9.0-13.1) drivers reported using cannabis prior to the collision. Regression results measuring exposure with blood and self-report data indicated that cannabis use alone was associated with a fourfold increased (OR 4.11; 95 % CI: 1.98-8.52) odds of a collision; a regression relying on self-report measures only found no significant association.

Conclusions: Main findings confirmed that cannabis use increases collision risk and reinforces existing policy and educational efforts, in many high-income countries, aimed at reducing driving under the influence of cannabis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Accidents, Traffic / prevention & control
  • Accidents, Traffic / statistics & numerical data*
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Cross-Over Studies
  • Emergency Service, Hospital*
  • Female
  • Humans
  • Male
  • Marijuana Smoking / adverse effects*
  • Middle Aged
  • Nova Scotia / epidemiology
  • Ontario / epidemiology
  • Qualitative Research
  • Risk Assessment
  • Wounds and Injuries / epidemiology
  • Wounds and Injuries / etiology
  • Young Adult