Longitudinal study of cognition among adolescent marijuana users over three weeks of abstinence.

Background: Cognitive deficits that persist up to a month have been detected among adult marijuana users, but decrements and their pattern of recovery are less known in adolescent users. Previously, we reported cognitive deficits among adolescent marijuana users after one month of abstinence (Medina, Hanson, Schweinsburg, Cohen-Zion, Nagel, & Tapert, 2007). In this longitudinal study, we characterized neurocognitive changes among marijuana-using adolescents across the first three weeks of abstinence.

Method: Participants were adolescent marijuana users with limited alcohol and other drug use (n=19) and demographically similar non-using controls (n=21) ages 15-19. Participants completed a brief neuropsychological battery on three occasions, after 3days, 2weeks, and 3weeks of stopping substance use. Abstinence was ascertained by decreasing tetrahydrocannabinol metabolite values on serial urine drug screens. Verbal learning, verbal working memory, attention and vigilance, and time estimation were evaluated.

Results: Marijuana users demonstrated poorer verbal learning (p<.01), verbal working memory (p<.05), and attention accuracy (p<.01) compared to controls. Improvements in users were seen on word list learning after 2weeks of abstinence and on verbal working memory after 3weeks. While attention processing speed was similar between groups, attention accuracy remained deficient in users throughout the 3-week abstinence period.

Conclusions: This preliminary study detected poorer verbal learning and verbal working memory among adolescent marijuana users that improved during three weeks of abstinence, while attention deficits persisted. These results implicate possible hippocampal, subcortical, and prefrontal cortex abnormalities.