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.