New research suggest early, heavy marijuana users may have persistent driving impairment

This new CNN article covers some interesting new driving research, although like lots of media this CNN piece — and especially its headline (“Weed impairs driving skills long after the high is gone”) — obscures some nuances of the research.   I always recommend checking out the original research, which here appears in the journal Drug and Alcohol Dependence.  The research article is headlined “Recreational cannabis use impairs driving performance in the absence of acute intoxication,” and here is its abstract:

Background

Across the nation, growing numbers of individuals are exploring the use of cannabis for medical or recreational purposes, and the proportion of cannabis-positive drivers involved in fatal crashes increased from 8 percent in 2013 to 17 percent in 2014, raising concerns about the impact of cannabis use on driving. Previous studies have demonstrated that cannabis use is associated with impaired driving performance, but thus far, research has primarily focused on the effects of acute intoxication.

Methods

The current study assessed the potential impact of cannabis use on driving performance using a customized driving simulator in non-intoxicated, heavy, recreational cannabis users and healthy controls (HCs) without a history of cannabis use.

Results

Overall, cannabis users demonstrated impaired driving relative to HC participants with increased accidents, speed, and lateral movement, and reduced rule-following. Interestingly, however, when cannabis users were divided into groups based on age of onset of regular cannabis use, significant driving impairment was detected and completely localized to those with early onset (onset before age 16) relative to the late onset group (onset ≥16 years old). Further, covariate analyses suggest that impulsivity had a significant impact on performance differences.