Cannabis in your blood stream doesn’t mean you’re stoned

published on November 2, 2016 in The Province

Re: Fatal car crashes triple among drivers high on marijuana after legalization in Colorado; double in Washington state, Oct. 30

Before raising the alarm on cannabis-impaired motor vehicle accidents, the stats presented in this article require additional clarification and contextualization.

Unlike alcohol, for which there is a close correlation between blood-alcohol content and impairment, there is no defined standard of impairment for cannabis.

Determining whether or not these drivers were impaired by cannabis is further complicated by the fact that tetrahydrocannabinol (THC) “” the primary psychoactive component in cannabis “” can be detected in the blood several days and even weeks after consuming cannabis.

This means that the observed increases in the proportion of fatally injured drivers testing positive for cannabis in these states might not indicate increases in cannabis-impaired driving, but rather general increases in cannabis use following legalization.

This is particularly plausible when we take into consideration the overall rate of motor vehicle accidents over time. Surveillance for cannabis among drivers in Colorado and Washington likely increased with legalization.

While close monitoring of cannabis and driving will be a top public health priority following legalization in Canada, it is important that we carefully consider the context and limitations of this type of data.

Stephanie Lake and M-J Milloy, Urban Health Research Initiative, B.C. Centre for Excellence in HIV/AIDS

View the full article