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Addiction. 2019 May 20. doi: 10.1111/add.14663. [Epub ahead of print]

Cannabis use as a risk factor for causing motor vehicle crashes: a prospective study.

Author information

1
Vancouver General Hospital & The University of British Columbia, Vancouver, British Columbia.
2
The University of British Columbia, Vancouver, British Columbia.
3
University of Victoria, Victoria, British Columbia.
4
Dalhousie University, Halifax, Nova Scotia.
5
Centre for Addiction and Mental Health, Toronto & University of Toronto, Toronto, Ontario.
6
Kelowna General Hospital & The University of British Columbia, Kelowna, British Columbia.
7
Royal Columbian Hospital & The University of British Columbia, New Westminster, British Columbia.
8
Victoria General Hospital & The University of British Columbia, Victoria, British Columbia.
9
Institute of Forensic Medicine, Justus Liebig University, Giessen, Germany.

Abstract

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.

PMID:
31106494
DOI:
10.1111/add.14663

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