Impaired Driving Causes More Than Half of All Driver-Related Injuries: Study

More than one-fifth of all injured drivers test positive for the presence of two or more mood-altering substances, researchers found.

A new study suggests that more than half of all driver injuries in motor vehicle accidents could involve individuals under the influence of alcohol, cannabis, opioids or other impairing substances.

The findings were published by Canadian researchers in the Journal of the American Medical Association (JAMA) on April 22, examining the prevalence of substance use among injured drivers by analyzing blood samples from more than 8,000 individuals, to identify the presence of impairing substances at the time of their crash.

Each year, more than 1.2 million people die in auto accidents, and many of these fatalities are associated with driving under the influence of mood-altering substances. However, detecting drug and alcohol impairment is challenging, as it often requires collecting biological samples such as saliva, urine or blood, which can be difficult to obtain, vary in reliability, and may be influenced by the circumstances under which testing occurs.

In the new study, researchers looked at blood samples from 8,328 drivers treated at 15 Canadian trauma centers between January 2019 and June 2023.

The team, led by Jeffrey Brubacher of the University of British Columbia, tested for THC, alcohol, stimulants, opioids and depressants.

Findings showed that 54.9% of drivers tested positive for at least one impairing substance, including 28.4% for depressants, 16.3% for THC, 16.1% for alcohol, 12.7% for stimulants and 10.9% for opioids. Additionally, 21.6% of drivers tested positive for two or more substance classes.

Substances were detected less frequently in drivers aged 75 and older, as well as those younger than 19. THC was most commonly found in drivers aged 19 to 24, alcohol in those aged 19 to 34, stimulants in drivers aged 35 to 44, opioids in those aged 55 to 64 and depressants in drivers aged 65 to 74.

Male and female drivers had a similar overall prevalence of substance use. However, males were more likely to have used alcohol, cannabis and stimulants, while females were more likely to have used depressants.

The study also found substantial geographic variation in the prevalence of substance use among injured drivers. Rural drivers were more likely to use alcohol, stimulants, depressants, opioids or multiple classes of substances. 

“These findings suggest that impaired driving remains a substantial road safety concern in Canada,” Brubacher said. “Continued monitoring is required to develop rational targeted interventions and to evaluate the effectiveness of prevention measures.”

Substance Use and Road Safety

Alcohol use has long been associated with a higher risk of auto accidents, with a 2024 study revealing that one in five child deaths from car crashes involved a drunk driver.

The legalization of cannabis has also raised serious concerns about accident risks, with research finding cannabis legalization associated with an increase in auto accidents throughout Canada, following its nationwide legalization in 2018.

Earlier this month, new research from the American Automobile Association (AAA) suggested that smartphone apps could be used to monitor driving behavior, helping drivers identify and reduce risky habits, and offering a potential solution to lower the number of accidents across the country.