Marijuana Law, Policy & Reform

Editor: Douglas A. Berman
Moritz College of Law

Thursday, January 16, 2020

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:


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.


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.


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.


Chronic, heavy, recreational cannabis use was associated with worse driving performance in non-intoxicated drivers, and earlier onset of use was associated with greater impairment. These results may be related to other factors associated with early exposure such as increased impulsivity.

Recreational Marijuana Data and Research | Permalink


The title of the original article is very misleading because it suggests that cannabis ALWAYS impairs driving performance even in the absence of “acute intoxication”; it should have included words such as “in some cases.” What the article actually says is that impairment was observed only among heavy users who had begun using before age 16—a small subset of all users. It also mentions “impulsivity” as a factor in impairment, raising the possibility that it was that same impulsivity that caused these young people to try cannabis at such a young age.

Posted by: Richard Kennedy | Jan 17, 2020 8:08:31 AM

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