Article by Lift
Cannabis legalization poses considerable risks for drivers and policy makers, with multiple investigations converging on the conclusion that cannabis intoxication increases road traffic accidents and fatalities, likely due to a reduction in attention, reaction speed, and judgement of drivers (for a Lift review of the research see here).
Countries around the globe have implemented a range of policies regulating driving under the influence of cannabis. For instance, Australia prohibits driving under any detectable level of THC, whereas Switzerland has a more lax limit of 2.2 ng/ml. Across the U.S., states have imposed limits ranging from zero to 5 ng/ml.
Arguments for a zero-level tolerance posit that exact measurement of cannabis blood levels is not possible due to technological limitations and a great variability in how individuals metabolize the drug, added to the fact that even low levels of cannabinoids can impair driving significantly (especially if other substances like alcohol are also ingested).
Arguments for specific limits, on the other hand, are centered around pragmatic factors and findings that THC and other cannabis metabolites can remain detectable for nearly a week, presumably long after any psychoactive effects can still be felt. Some concerns shared by both sides revolve around the need for blood samples for adequate ruling of intoxication, due to the associated medical risks.
A recent investigation from the University of Marseille and the Service de Pharmacocinétique Toxicocinétique provides new important data for this ongoing debate. The team, led by Dr. Amélie Marsot, described in great detail the pharmacokinetic profiles of THC and its metabolites in saliva, blood plasma, and urine during the first 72 hours. Their report can be accessed for free in the Journal of Pharmacy and Pharmaceutical Sciences.