Association of cannabis edibles-induced impairment in simulated driving with THC in blood and saliva: Implications for road safety

Converging evidence suggests that the use of cannabis increases the risk of motor vehicle collisions. At present, deterring driving under the influence of cannabis involves detection of THC (the psychoactive component of cannabis) in blood and saliva. Most of the evidence we have to inform the legal cut-offs of THC in blood and saliva are derived from studies in which people smoked cannabis. It is known that about 40% of cannabis users consume their product in food, which has implications for road safety because levels of THC in blood are lower after eating cannabis as compared to smoking cannabis. Despite this, cannabis taken by mouth is intoxicating. This suggests that it may be difficult to detect THC in blood and saliva in people who drive after using cannabis edibles. More studies are needed to delineate the relationship between THC in blood and saliva and changes in driving after using cannabis edibles. In the present study participants drove a high fidelity driving simulator before and after ingesting a legally purchased cannabis edible that they brought to the lab for consumption. Blood was collected for detection of levels of THC and CBD and THC in saliva was tested. The present study was the first investigation into the effects of cannabis edibles on simulated driving, and the association of changes in driving with THC in blood and detection of THC in saliva. The results of the present study will have important implications for road safety and the results of this study will be disseminated to the wider public.            

Use of cannabis edibles is on the rise, yet little is known about the effects of cannabis edibles on driving. In this first study of the impact of cannabis edibles on driving, participants were invited to consume their usual, preferred, legally purchased cannabis edible prior to driving. We found that driving was impacted; associated blood THC levels were significantly elevated but remained below the legal threshold for driving. This suggests that ecologically valid doses of cannabis edibles are intoxicating and it may be difficult to detect this at the roadside. We published 1-2 papers from this study.

This study was funded by the Ministry of Transportation of Ontario