Dagga doubles accident risk for drivers

Over 10 million people age 12 or older are estimated to have driven under the influence of illicit drugs in the prior year, according to a National Survey on Drug Use and Health.

While dagga is the most commonly detected non-alcohol drug in drivers, its role in causing crashes has remained in question.

To examine the link between dagga use by drivers and risk of a car accident, researchers at Columbia University did a meta-analysis of nine epidemiologic studies and found that drivers who test positive for marijuana, or report driving within three hours of dagga use, are more than twice as likely as other drivers to be involved in motor vehicle crashes.

Increased risk

The researchers also found evidence that crash risk increases with the concentration of dagga-produced compounds in the urine and the frequency of self-reported dagga use.

According to the investigators 8 of 9 studies found that drivers who use dagga are significantly more likely to be involved in crashes than drivers who do not. Only one small case-control study conducted in Thailand, where the prevalence of dagga use is far lower than reported elsewhere, was the exception.

Full study findings are published online in Epidemiologic Reviews.

The analysis indicates that 28% of fatally injured drivers and more than 11% of the general driver population tested positive for non-alcohol drugs, with dagga being the most commonly detected substance.

Dagga for medical use

Guohua Li, MD, DrPh, professor of Epidemiology at Columbia University's Mailman School of Public Health, and senior author points out that although this analysis provides compelling evidence for an association between dagga use and crash risk, one should be cautious in inferring causality from these epidemiologic data alone.

 However, if the crash risk associated with dagga is confirmed by further research, this is likely to have major implications for driving safety and public policy. It also would play a critical role in informing policy on the use of medical dagga.

"Given the ongoing epidemic of drug-impaired driving and the increased permissibility and accessibility of dagga for medical use in the US, it is urgent that we better understand the role of dagga in causing car accidents."

(Eurek Alert, October 2011) 

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