Alcohol and cannabis remain the substances most widely used by adolescents. Better understanding of the dynamic relationship between trajectories of substance use in relation to neuropsychological functioning is needed. The aim of this study was to examine the different impacts of within- and between-person changes in alcohol and cannabis use on neuropsychological functioning over multiple time points.

Hierarchical linear modeling examined the effects of alcohol and cannabis use on neuropsychological functioning over the course of 14 years in a sample of 175 adolescents (aged 12–15 years at baseline).

Time-specific fluctuations in alcohol use (within-person effect) predicted worse performance across time on the Wechsler Abbreviated Scale of Intelligence Block Design subtest (B = −.05, SE = .02, p = .01). Greater mean levels of percent days of cannabis use across time (between-person effect) were associated with an increased contrast score between Delis–Kaplan Executive Function System Color Word Inhibition and Color Naming conditions (B = .52, SE = .14, p < .0001) and poorer performance over time on Block Design (B = −.08, SE = .04, p = .03). Neither alcohol and/nor cannabis use over time was associated with performance in the verbal memory and processing speed domains.

Greater cumulative cannabis use over adolescence may be linked to poorer inhibitory control and visuospatial functioning performance, whereas more proximal increases in alcohol consumption during adolescence may drive alcohol-related performance decrements in visuospatial functioning. Results from this prospective study add to the growing body of literature on the impact of alcohol and cannabis use on cognition from adolescent to young adulthood.