Cannabis Use and Driving Performance

Dahlgren, M. K., Sagar, K. A., Smith, R. T., Lambros, A. M., Kuppe, M. K., & Gruber, S. A. (2020). Recreational cannabis use impairs driving performance in the absence of acute intoxication. Drug and Alcohol Dependence, (Advanced online version).

Increased legalization of medical and recreational cannabis has led to concern about a possible proliferation of cannabis-impaired drivers. Dahlgren and colleagues noted that most of the research on the effects of cannabis for driving have focused on acutely intoxicated individuals rather than the non-immediate effects of heavy recreational use. They administered tests in a driving simulator to three groups of participants – healthy individuals without a history of cannabis use, and non-intoxicated heavy recreational users with either early onset (started before age 16) or late onset (started at age 16 or later). All participants were asked to refrain from cannabis for at least 12 hours before the study. At the time of the study, they were administered a urine test (to screen for cannabis and other recent drug use) as well as a measure of impulsivity. The researchers found that the early onset group showed significantly more impaired driving as compared to the other two groups. For example, they were more likely to exceed speed limits, miss stop signs, drive out of lane, have collisions, and hit pedestrians. However, many of these group differences disappeared once the researchers controlled for impulsivity. The authors suggested that more attention should focus on the effects of cannabis use in the absence of acute intoxication, as well as the neurological implications of cannabis for early onset users and possible associations between cannabis use and impulsivity.

Making Connections

Cerebral Cortex
Confounding Variable
Critical Period
Drug use
Executive Function
Personality traits

Media Supplement

This NPR podcast discusses the challenges involved in developing and implementing a breathalyzer to identify cannabis-impaired driving. (4 min)

This PBS News Hour clip explores myths -- and current scientific research findings -- about how marijuana affects the brain. (9 min 21 sec)