Tags:  Cannabis, marijuana, driving under the influence, intoxication, risk perception

 

The problem:  Legalization of cannabis has made its usage, including while driving, more common among the general population. But because THC impairs psychomotor functioning, driving under the influence of cannabis (DUIC) is a public safety concern that calls for research and intervention.

 

Why do this study?  Most cannabis users believe that driving under the influence of cannabis is less dangerous than driving under the influence of alcohol. Some believe DUIC is safe, and some even believe DUIC is safer than driving while sober. These views are all based on an individual’s perception of how much cannabis is ‘safe’ for driving. This study explores whether such self-reported quantities predict a cannabis user’s actual frequency of DUIC.

 

The study: In 2017, 3,010 participants, who had used cannabis in the past month and had a history of DUIC since age 18, completed an online survey. Questions assessed participants’ patterns of cannabis usage as well as perceptions and patterns of DUIC. Those who used cannabis more frequently were more likely to report DUIC in the past month and disclose DUIC at higher levels of intoxication. In terms of perceptions of DUIC, on a scale of 0 (“Sober”) to 10 (“So high that you throw up”), those with no DUIC in the past month perceived an intoxication level of 3 to be safe for driving while those with DUIC on 20-30 days of the past month perceived an intoxication level of 8 to be safe for driving. The greater the level of intoxication an individual perceived to be safe, the more likely the individual was to frequently DUIC in the past month. For example, increasing the level of intoxication perceived as safe by one made DUIC 20-30 days in the past month 68% more likely for an individual.

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Conclusions:  DUIC patterns varies greatly among cannabis users. However, the intoxication level perceived as safe for driving is a good predictor of how frequently a person DUIC in the past month. An individual’s usual level of intoxication is not as relevant in predicting frequency.

 

What does this study add?  These conclusions have useful implications for future research, preventative messaging, the identification of high-risk groups, and public health in general.

 

Funder:  This study received funding from the National Institute on Drug Abuse (NIDA) and the National Institute on Alcohol Abuse and Alcoholism (NIAAA). These organizations were not involved in study design; collection, analysis, and interpretation of data; report writing; or the decision to submit the article for publication.

 

Author conflicts:  None.

 

Commentary: (David Casarett MD)  There’s not much question that driving while stoned is a bad idea.  We have dozens of studies of real-life driving on a closed course as well as driving simulators.  There’s even been one study in a flight simulator, just in case anyone thinks that being high while…well…being high is a good idea. This study doesn’t tell us what level is safe—that wasn’t the point.  But it does tell us that different people have very different ideas about what is safe, and that’s a problem.