Frequent cannabis users do not display impaired driving after at least 48 hours of abstinence, found a new study published in Psychopharmacology.
“The findings 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,” said senior author of the study, Thomas Marcotte, Ph.D., professor of psychiatry at UC San Diego School of Medicine in a press release.
Around 15% of Americans currently use cannabis, and around 75% live in states where it is legally available. Understanding more about the effects of cannabis on daily activities is crucial for maintaining public safety.
Tetrahydrocannabinol (THC), the psychoactive compound in cannabis, can be detected in blood for several days to weeks following use. Until now, it has remained unclear whether detectable levels of THC in the blood impair driving even when not actively high. In the current research, investigators set out to answer this question.
They conducted two studies: one involving 191 healthy cannabis users completing a 25-minute simulated drive followed by over 48 hours of abstinence, and the other: involving a subset of 18 frequent users as well as 12 non-users as controls who completed identical driving measures. The main study outcome for both studies was Composite Drive Score, a measure of driving performance comprising key driving-related variables.
“We 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,” said first author of the study, Kyle Mastropietro, a graduate student in the San Diego State University/UC San Diego Joint Doctoral Program in Clinical Psychology, in a press release.
The findings have implications for future policies for assessing cannabis intoxication, wrote the researchers in their study. They added that future studies should explore whether short-term residual effects exist for driving performance via the use of more complex driving tasks, larger non-using control groups, and better controlling for possible confounders like cannabis withdrawal effects.
Sources: EurekAlert, Psychopharmacology