Correlation Between THC Levels and Motor Vehicle Accidents: An Examination

by Roman Cheplyk
Monday, September 25, 2023
Correlation Between THC Levels and Motor Vehicle Accidents: An Examination

The primary aim of this study was to examine the influence of cannabis legalization on the detection of tetrahydrocannabinol (THC) in injured drivers

The research sought to tackle concerns regarding the potential rise in motor vehicle accidents (MVAs) linked to cannabis intoxication, given the well-known cognitive and performance-impairing effects of cannabis. While previous investigations conducted in various American states produced mixed outcomes, this study concentrated on scrutinizing real-world accident data from British Columbia (B.C.).

The study focused on instances where drivers had sustained injuries and had their blood samples taken as part of their medical care at one of four participating trauma centers in B.C. Specifically, the analysis considered cases in which blood samples were accessible for examination within six hours of the accident. Out of a total of 5,699 possible cases, 4,409 cases (77.4%) were incorporated into the study. These cases were categorized into three groups: 3,550 cases before cannabis legalization (January 2013-September 2018), 70 cases during the month when legalization was put into effect (October 2018), and 789 cases after legalization (November 2018 to March 2020).

The study's findings unveiled several noteworthy insights:

  1. There was no substantial alteration in the proportion of drivers impaired by alcohol (i.e., blood alcohol >0.08%) prior to and after cannabis legalization (9.3% vs. 8.1%). The adjusted prevalence ratio stood at 0.98 (95% CI 0.74-1.30).

  2. Nevertheless, there was a marked increase in the percentage of drivers with detectable levels of blood cannabis after legalization:

    a) Those with blood cannabis levels exceeding 2 ng/ml (the threshold for a summary conviction offense) escalated from 4.7% to 8.6%. The adjusted prevalence ratio was 2.29 (95% CI 1.52-3.45).

    b) Drivers with blood cannabis levels surpassing 5 ng/ml (the threshold for a summary or indictable offense) surged from 1.1% to 3.5%. The adjusted prevalence ratio was 2.05 (95% CI 1.00-4.18).

It's noteworthy that summary offenses are less serious than indictable offenses, entailing comparatively lighter penalties, akin to the distinction between misdemeanors and felonies in the American legal system.

However, it's imperative to grasp that the mere presence of THC in a driver's bloodstream does not inherently imply that it caused or elevated the risk of a collision. The study had its constraints, including the exclusion of fatal cases, instances involving minor or no injuries, and those not transported to the participating trauma centers. Furthermore, the study did not furnish details on the mode of cannabis consumption or the prior cannabis usage of the drivers, factors that can influence blood THC levels. Additionally, it's worth considering that cannabis use in B.C., both pre- and post-legalization, tends to exceed the national average, suggesting that the findings may not be directly transferable to other regions. Nevertheless, these results imply a heightened correlation between cannabis use and motor vehicle accidents following legalization.

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