Researchers from the University of Colorado School of Medicine have found that moderate marijuana use among teenagers is associated with reduced cognitive function.
For the study, the researchers analyzed 1,192 adolescents from 596 families in both Dever and San Diego. While 64% of the participants were male, the researchers say that their sample was ethnically diverse, with non-Hispanic white Americans accounting for just 45% of the study’s participants.
Families chosen for the study included at least one sibling who reportedly used cannabis for an average of 7-9 days per month. This is significant given previous family-based studies have instead used samples of infrequent cannabis users- those using the substance just 1-2 days per month.
While drug use was measured via clinical interviews, cognitive abilities were assessed via a series of neuropsychological tests. All in all, the data was collected over two periods. During the first period of data collection between 2001 and 2006, participants had an average age of 17, whereas, in the second period between 2008 and 2013, the same participants had an average age of 24.
After adjusting for several factors, the researchers found that those who used cannabis earlier on and more frequently tended to perform worse in cognitive tests. This was especially true for tests investigating verbal memory. Moreover, these results remained the case even after accounting for familial factors shared by siblings and alcohol use.
As such, the researchers concluded that moderate adolescent cannabis use may have adverse effects on cognitive abilities in the developing brain, and specifically for verbal memory. The researchers thus hope that their findings will go on to inform future study designs as well as public health decisions, especially given the increasing legality and availability of both recreational and medical cannabis products in many US states and countries around the world.