THC was found in more fatally injured Ontario drivers than alcohol between 2016 and 2018 | Research

The takeaway

In a study of 921 driver fatalities in Ontario, more tested positive for THC (251) than for alcohol (241), with 38% of positive cases involving multiple substances.

Policymakers working on impaired driving laws, road safety researchers, anyone concerned about cannabis and driving

251 driver fatalities tested positive for THC vs 241 for alcohol

What the researchers found

Among 921 driver fatalities, 53.7% tested positive for at least one substance. THC positivity (251 cases) exceeded alcohol (241 cases). Alcohol-related fatalities clustered on weekends in single-vehicle crashes, while THC-positive fatalities were spread throughout the week and more often involved multi-vehicle crashes.

Why it matters

The finding that THC now appears in more fatally injured drivers than alcohol signals a shift in impaired driving patterns that requires new prevention strategies beyond traditional alcohol-focused approaches.

The numbers in context

921 driver fatalities; 53.7% tested positive for a substance; 251 THC-positive; 241 alcohol-positive; 235 positive for other drugs; 38% of positive cases had multiple substances

How the study worked

Toxicological analysis of postmortem blood samples from 921 drivers who died in crashes in Ontario, Canada from January 2016 through December 2018, with demographic and crash characteristics coded into a database.

What this study cannot tell us

Postmortem THC detection does not prove impairment at time of crash. Single province data may not generalize nationally. No comparison with non-fatal crashes or general driving population.

How to read the evidence

Large toxicological study of real-world driver fatalities with comprehensive testing

When this study was published

Published in 2021 using 2016-2018 data from Ontario. Cannabis was legalized in Canada in October 2018, so this data spans both pre- and post-legalization periods.

The bigger picture

As cannabis legalization expands in Canada and elsewhere, this data provides a baseline for monitoring how changing cannabis laws affect road safety and whether new intervention strategies are needed.

Questions still open

Has the pattern changed since cannabis legalization in Canada (October 2018)? What THC concentrations were found, and do they correlate with crash type? Would roadside impairment testing have prevented these crashes?

Common questions

Is THC now more common than alcohol in driver fatalities?

In this Ontario study, yes. THC was detected in 251 driver fatalities compared to 241 for alcohol between 2016 and 2018. However, detection does not prove impairment at the time of the crash.

Do cannabis-impaired crashes look different from alcohol-impaired crashes?

This study found alcohol-related fatalities clustered on weekends and were more often single-vehicle crashes, while THC-positive fatalities were spread throughout the week and more often involved multi-vehicle collisions.

Read the original research

Cannabis, alcohol and other drug findings in fatally injured drivers in Ontario.

Traffic injury prevention, 22(1), 1-6

View on PubMed ↗Publisher’s paper ↗

Citation

Beirness, Douglas J; Gu, Kai Wen; Lowe, Nicholas J; Woodall, Karen L; Desrosiers, Nathalie A; Cahill, Brent; Porath, Amy J; Peaire, Amy. (2021). Cannabis, alcohol and other drug findings in fatally injured drivers in Ontario.. Traffic injury prevention, 22(1), 1-6. https://doi.org/10.1080/15389588.2020.1847281