Study: Frequent Cannabis Consumers Do Not Display Driving Impairments After 48 Hours of Abstinence 

A study published in July in the journal Psychopharmacology found that frequent cannabis consumers did not display impairments in driving performance after at least 48 hours of abstinence.  

The researchers from the Center for Medicinal Cannabis Research (CMCR) at the University of California San Diego School of Medicine performed two studies: the first, a randomized clinical trial, which, using a driving simulator, assessed driving performance in a sample of 191 cannabis consumers, all of whom had abstained for at least 48 hours, and a second study that compared a subset of the most frequent cannabis consumers from the first study with a smaller comparison group of non-consumers. 

In a statement, first-author Kyle Mastropietro, a graduate student in the San Diego State University/UC San Diego Joint Doctoral Program in Clinical Psychology, said the researchers “did not find any relationship between driving performance, and cannabis use history or time of abstinence, nor blood THC concentrations.” 

“Of note, the most intensive users from the group, who mostly used cannabis daily and smoked an average of four joints per day, did no worse during this period of abstinence than a healthy, non-using comparison group.” — Mastropietro in a statement 

Thomas Marcotte, Ph.D., professor of psychiatry at UC San Diego School of Medicine and the study’s senior author, said in a statement that “the findings reinforce the challenges in relating findings from cognitive testing in very frequent users who are abstinent to how they might function during real-world, overlearned behaviors like driving,” and “add to the growing body of evidence that relying on blood THC concentrations in regular cannabis users as possible indicators of impairment is not justified, given that THC may be detectable many days (or longer) after use.” 

The authors note that this study was done in a controlled laboratory environment, did not address all possible driving scenarios, and the non-consumer comparison group was small.