AimWe 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.DesignProspective case–control study.SettingTrauma centres in British Columbia, Canada.ParticipantsInjured drivers who required blood tests for clinical purposes following a motor vehicle collision.MeasurementsExcess whole blood remaining after clinical use was obtained and broad‐spectrum toxicology testing performed. The analysis quantified alcohol and THC and gave semiquantitative levels of other impairing drugs and medications. Police crash reports were analysed 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: OR) of crash responsibility in drivers with 0 < THC < 2 ng/ml, 2 ng/ml ≤ THC < 5 ng/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.FindingsWe 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 < 2 ng/ml or 2 ≤ THC < 5 ng/ml. In drivers with THC ≥ 5 ng/ml, the adjusted OR was 1.74 [95% confidence interval (CI) = 0.59–6.36; P = 0.35]. There was significantly increased risk of crash responsibility in drivers with blood alcohol concentration (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).ConclusionsIn this sample of non‐fatally injured motor vehicle drivers in British Columbia, Canada, there was no evidence of increased crash risk in drivers with Δ‐9‐tetrahydrocannabinol < 5 ng/ml and a statistically non‐significant increased risk of crash responsibility (odds ratio = 1.74) in drivers with Δ‐9‐tetrahydrocannabinol ≥ 5 ng/ml.
Background Many medications impair driving skills yet their influence on collision risk remains uncertain. We aimed to systematically investigate the risk of collision responsibility associated with common classes of prescription medications.Methods In this population-based case-control study we analysed linked driving and health records in British Columbia, Canada from Jan 1, 1997, to Dec 31, 2016. The study cohort included all drivers involved in an incident collision (defined as first collision after 3 collision-free years) that resulted in a police report. We scored police collision reports and classified drivers as responsible for the collision (cases) or not responsible (controls); drivers with indeterminate scores were excluded. We used logistic regression to determine odds of collision responsibility in drivers with current prescriptions for medications of interest versus drivers without prescriptions. To explore whether risk of collision responsibility was related to medication effect or driver factors, we compared risk in current medication users versus past users. To study whether drivers developed tolerance to medication effects, we compared risk in new (first 30 days of a prescription) versus established users.
FindingsDuring the study period, 4 906 925 drivers had their driving licence linked to health records; of these drivers, 747 662 unique drivers were involved in 837 919 incident collisions between Jan 1, 2000, and Dec 31, 2016. 382 685 drivers responsible for the collision (cases) and 332 259 drivers not responsible (controls) were included in the final analysis; 122 975 drivers with indeterminate responsibility were excluded. We found increased risk of collision responsibility in drivers prescribed sedating antipsychotics (adjusted odds ratio [aOR] 1•35 [98•75% CI 1•25-1•46]), long-acting benzodiazepines (aOR 1•30 [1•22-1•38]), short-acting benzodiazepines (aOR 1•25 [1•20-1•31]), and high-potency opioids ( aOR 1•24 [1•17-1•30]). Among medications used for medical indications, the highest risk was seen in drivers prescribed neurological medications: cholinergic drugs (aOR 1•83 [1•39-2•40]), anticholinergic agents for Parkinson's disease (aOR 1•45 [1•08-1•96]), dopaminergic agents (aOR 1•20 [1•04-1•38]), and anticonvulsants (aOR 1•20 [1•14-1•26]). People currently taking benzodiazepines, non-sedating antidepressants, high-potency opioids, and anticonvulsants had increased risk compared with past users, and we did not find increased risk in new compared with established users of these drugs.Interpretation Drivers prescribed benzodiazepines or high-potency opioids are at increased risk of being responsible for collisions and this risk does not decrease over time. Several other classes of medications are associated with increased risk, but this association might be independent of medication effect. These findings can guide medication warnings and prescription choices and inform public education campaigns targeting impaired driving.
The results provide evidence that British Columbia's new child safety restraint law was associated with fewer injuries among children covered by the new laws.
BackgroundOpioids increase the risk of traffic crash by limiting coordination, slowing reflexes, impairing concentration and producing drowsiness. The epidemiology of prescription opioid use among drivers remains uncertain. We aimed to examine population-based trends and geographical variation in drivers’ prescription opioid consumption.MethodsWe linked 20 years of province-wide driving records to comprehensive population-based prescription data for all drivers in British Columbia (Canada). We calculated age- and sex-standardised rates of prescription opioid consumption. We assessed temporal trends using segmented linear regression and examined regional variation in prescription opioid use using maps and graphical techniques.ResultsA total of 46 million opioid prescriptions were filled by 3.0 million licensed drivers between 1997 and 2016. In 2016 alone, 14.7% of all drivers filled at least one opioid prescription. Prescription opioid use increased from 238 morphine milligram equivalents per driver year (MMEs/DY) in 1997 to a peak of 834 MMEs/DY in 2011. Increases in MMEs/DY were greatest for higher potency and long-acting prescription opioids. The interquartile range of prescription opioid dispensation by geographical region increased from 97 (Q1=220, Q3=317) to 416 (Q1=591, Q3=1007) MMEs/DY over the study interval.ImplicationsPatterns of prescription opioid consumption among drivers demonstrate substantial temporal and geographical variation, suggesting they may be modified by clinical and policy interventions. Interventions to curtail use of potentially impairing prescription medications might prevent impaired driving.
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