Presence Of THC In Blood is Not Associated With Crash Culpability, Finds Study

According to a new study, drivers who test positive for THC do not possess a significantly increased risk of being responsible for a non-fatal motor vehicle accident.

For the study, researchers at the University of British Columbia compared the likelihood of crash responsibility in drivers testing positive for THC and/or other substances as compared to drug-free drivers over a six-year period (2010 to 2016).

As reported on by NORML, the state found that, “In this multi-site observational study of non-fatally injured drivers, we found no increase in crash risk, after adjustment for age, sex, and use of other impairing substances, in drivers with THC<5ng/ml. For drivers with THC>5ngml there may be an increased risk of crash responsibility, but this result was statistically non-significant and further study is required. … Our findings … suggest that the impact of cannabis on road safety is relatively small at present time.”

By contrast, authors reported, “There was a significantly increased risk for drivers who used alcohol, sedating medications, or recreational drugs others than cannabis.” Drivers who tested positive for the concurrent use of cannabis and alcohol possessed a higher risk of accident as compared to drivers who tested positive for alcohol alone – a finding that is consistent with other studies.

The full text of the study, titled “Cannabis use as a risk factor for causing motor vehicle crashes: A prospective study,” has been published in the journal Addiction.

The full abstract of the study can be found below:

AIM:

We conducted a responsibility analysis to determine whether drivers injured in motor vehicle collisions who test positive for Δ-9-tetrahydrocannabinol (THC) or other drugs are more likely to have contributed to the crash than those who test negative.

DESIGN:

Prospective case-control study.

SETTING:

Trauma centres in British Columbia, Canada.

PARTICIPANTS:

Injured drivers who required blood tests for clinical purposes following a motor vehicle collision.

MEASUREMENTS:

Excess whole blood remaining after clinical use was obtained and broad spectrum toxicology testing performed. The analysis quantified alcohol and THCand gave semi-quantitative levels of other impairing drugs and medications. Police crash reports were analyzed to determine which drivers contributed to the crash (responsible) and which were “innocently involved” (non-responsible). We used unconditional logistic regression to determine the likelihood (Odds Ratio) of crash responsibility in drivers with 0<THC<2ng/mL, 2ng/mL≤THC<5ng/mL, and THC≥5 ng/mL (all versus THC=0 ng/mL). Risk estimates were adjusted for age, sex, and presence of other impairing substances.

FINDINGS:

We obtained toxicology results on 3005 injured drivers and police reports on 2318. Alcohol was detected in 14.4% of drivers, THC in 8.3%, other drugs in 8.9% and sedating medications in 19.8%. There was no increased risk of crash responsibility in drivers with THC<2ng/mL or 2≤THC<5ng/mL. In drivers with THC≥5ng/mL, the adjusted OR was 1.74 (95%CI=0.59-6.36;p=0.35). There was significantly increased risk of crash responsibility in drivers with BAC≥0.08% (OR=6.00;95%CI=3.87-9.75;p<0.01), other recreational drugs detected (OR=1.82;95%CI=1.21-2.80;p<0.01), or sedating medications detected (OR=1.45;95%CI=1.11-1.91;p<0.01).

CONCLUSIONS:

In this sample of non-fatally injured motor vehicle drivers in British Columbia, Canada, there was no evidence of increased crash risk in drivers with THC<5ng/mL and a statistically non-significant increased risk of crash responsibility (OR=1.74) in drivers with THC≥5ng/mL.

1 thought on “Presence Of THC In Blood is Not Associated With Crash Culpability, Finds Study”

  1. The testing devices roadside for Cannabis levels are non-significant as well, can’t be proven when the cannabis was consumed, it will take some time for tech to catch up.

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