Longitudinal changes in cognition in young adult cannabis users.

Introduction: Adolescent cannabis use (CU) is associated with impaired attention, executive function, and verbal learning/memory. These associations are generally observed in cross-sectional studies. Longitudinal studies of cannabis users are lacking.

Method: The present study examines associations between CU and cognition over time in chronic daily adolescent-onset CUs, as compared to nonusing controls. Both groups completed a neuropsychological battery at study intake and again 2 years later.

Results: Baseline group differences have been published and indicated deficits in verbal learning and memory, motivated decision-making, planning, and working memory in CUs. In this follow-up report, the longitudinal performance of users is compared to that of sustained nonusers using the same battery. At follow-up, the majority of CUs continued to report regular and heavy cannabis use. Relative impairments in the domains of working memory, planning and verbal memory remained stable, suggesting that these are enduring vulnerabilities associated with continued CU during young adulthood. Improvements in motivated decision-making were evident in both groups. In addition, CUs demonstrated relatively better performance on short-duration speeded tasks. An earlier age of CU onset was associated with poorer verbal learning and memory and planning performance over time.

Conclusions: Verbal learning and memory and planning processes, as well as their neural correlates, merit further scrutiny within etiological models of cannabis-induced cognitive impairments.