Cannabis-Involved Traffic Injury ER Visits Rose 475% in Ontario Over a Decade, Accelerating After Commercialization | Research

The takeaway

Cannabis-involved traffic injury ER visits in Ontario increased 475% from 2010 to 2021, with the sharpest rise after cannabis retail stores expanded, though absolute numbers remained small.

Traffic safety researchers, policymakers in legalization states, harm reduction advocates.

475% increase in cannabis-involved traffic ER visits, but still only 0.04% of total

What the researchers found

Annual rates of cannabis-involved traffic injury ER visits rose from 0.18 to 1.01 per 1,000 total motor vehicle collisions. Legalization with restrictions was associated with a 94% increase (aRR 1.94), while the commercialization/COVID period saw a 223% increase (aRR 3.23). Cannabis involvement remained rare overall (0.04% of traffic injury ER visits) compared to alcohol (0.8%). Males, ages 19-21, lowest-income neighborhoods, and prior cannabis-related ER visits were risk factors.

Why it matters

As jurisdictions legalize cannabis, tracking traffic safety outcomes is critical. This study suggests that the retail expansion phase, not initial legalization, may be when impaired driving increases most, though confounding with COVID-era changes in driving patterns complicates interpretation.

The numbers in context

947,604 traffic injury ER visits total. 426 (0.04%) had cannabis involvement. 7,564 (0.8%) had alcohol involvement. 475% increase in cannabis-involved rate over the study period. Males: aOR 3.38. Ages 19-21: aOR 4.67. Prior cannabis ER visit: aOR 8.03.

How the study worked

Repeated cross-sectional study of all traffic injury ER visits in Ontario, Canada (2010-2021) across three periods: pre-legalization, legalization with restrictions, and commercialization. Used quasi-Poisson models adjusting for season and time trends.

What this study cannot tell us

Cannabis involvement was documented in only 0.04% of visits, so small absolute changes produce large relative changes. The commercialization period coincided with COVID-19, confounding the analysis. Relies on clinician documentation of cannabis involvement, which likely underestimates true prevalence.

How to read the evidence

Population-level data from a universal healthcare system, but confounded by COVID-19 overlap with the commercialization period and very small absolute numbers.

When this study was published

Published 2023, using 2010-2021 data from Ontario, Canada.

The bigger picture

While the relative increase is dramatic, the absolute numbers are very small. Alcohol involvement in traffic injuries was 20 times more common than cannabis. The co-occurrence of commercialization with COVID-19, which changed driving patterns substantially, makes it hard to isolate the effect of expanded retail access.

Questions still open

How much of the increase is attributable to better detection and documentation rather than actual increases?
Did COVID-era changes in driving patterns inflate the commercialization-period estimates?

Common questions

Did cannabis legalization increase traffic injuries?

Cannabis-involved traffic injury ER visits rose significantly, but they remained extremely rare (0.04% of all traffic injuries). Alcohol involvement was 20 times more common.

When did the biggest increase happen?

The sharpest rise coincided with cannabis retail expansion and the COVID-19 pandemic, making it hard to separate the two factors.

Read the original research

Cannabis-Involved Traffic Injury Emergency Department Visits After Cannabis Legalization and Commercialization.

JAMA network open, 6(9), e2331551

View on PubMed ↗Publisher’s paper ↗

Citation

Myran, Daniel T; Gaudreault, Adrienne; Pugliese, Michael; Manuel, Douglas G; Tanuseputro, Peter. (2023). Cannabis-Involved Traffic Injury Emergency Department Visits After Cannabis Legalization and Commercialization.. JAMA network open, 6(9), e2331551. https://doi.org/10.1001/jamanetworkopen.2023.31551