Medical cannabis authorization was associated with slightly increased motor vehicle crash-related healthcare visits

After accounting for an initial decrease in MVC-related visits (-2.42/10,000 patients immediately post-authorization), there was a significant increasing trend (+0.89 events/10,000 relative to controls, p=0.0019). Overall, authorization was associated with an increase of 2.92 events/10,000 (95% CI: 0.64-5.19) over 6 months. The effect was largely driven by MVC-related emergency department visits (+0.80/10,000, p<0.001).

Matched cohort study of 29,153 medical cannabis patients and matched controls in Ontario, Canada (2014-2017). Linked to administrative health databases. Interrupted time series analysis comparing MVC-related healthcare visits 6 months before and after authorization.

This is one of the largest studies directly linking medical cannabis authorization to traffic safety outcomes using administrative health data. The small but significant increase in MVC-related visits has public health implications as medical cannabis programs expand.

The magnitude is small (about 3 extra MVC-related visits per 10,000 patients over 6 months), but at the population level of millions of cannabis users, this could translate to meaningful numbers. The initial decrease followed by gradual increase may reflect initial caution followed by normalization of driving behavior.

Observational design cannot prove cannabis caused crashes. Medical cannabis patients may differ from controls in unmeasured ways. Cannot determine impairment at time of crash. Short 6-month follow-up.