The main objective of this study was to investigate bidirectional associations between adolescent cannabis use and neurocognitive performance in a community sample of 294 young men from ages 13 to 20 years. The results showed that in early adolescence, and prior to initiation of cannabis use, poor short-term and working memory, but high verbal IQ, were associated with earlier age of onset of cannabis use. In turn, age of onset and frequency of cannabis use across adolescence were associated with (a) specific neurocognitive decline in verbal IQ and executive function tasks tapping trial and error learning and reward processing by early adulthood and (b) lower rates of high-school graduation. The association between onset of use and change in neurocognitive function, however, was found to be accounted for by cannabis use frequency. The authors concluded that the results support prevention efforts aimed at delaying onset and reducing frequency of cannabis use.
Castellanos-Ryan N, Pingault JB, Parent S, Vitaro F, Tremblay RE, Séguin JR: Adolescent cannabis use, change in neurocognitive function, and high-school graduation: A longitudinal study from early adolescence to young adulthood. Dev Psychopathol 29:1-14 (2016).