Project Summary. More people in the United States are addicted to cannabis than to any otherillicit drug, and prevalence of its use is rising, accompanied by a decline in its perceived harmamong adolescents. Important maturational changes in prefrontal cortex during adolescencemay make youth more vulnerable than adults to adverse effects from cannabis. Indeed,research shows impairments in memory performance and decision-making abilities of heavycannabis users, most of whom initiate use during adolescence. However, little is known abouthow decision-making and memory are affected across the trajectory from initial experimentationto development of cannabis addiction. Furthermore, there is controversy in the scientificliterature on whether the impairments in decision-making observed among heavy cannabisusers are due to the harmful effects of cannabis on brain functioning, or whether they may be anantecedent risk factor for the development of cannabis addiction. The principal goals of thisproposal are to determine whether: a) decision-making is an antecedent risk factor for cannabisaddiction; and b) what changes occur in decision-making and episodic memory along differentcannabis use trajectories. Participants will be 480 youth ages 14 to 15 at baseline, most ofwhom will have experimented with cannabis, but have yet to develop addiction. Over threeyears, their performance will be assessed on measures of decision-making and episodicmemory every 18 months and on their substance use and symptoms of cannabis addictionevery 9 months. Poorer decision-making at baseline is hypothesized to be associated withincreased risk of developing cannabis addiction during follow-up. Similarly, declines in decision-making during follow-up are hypothesized to be associated with increased severity of cannabisaddiction (i.e., more compulsive use and more negative consequences). Finally, those whoescalate in their cannabis consumption over time will show greater deterioration in their episodicmemory than observed in other (non-escalating or desisting) cannabis use trajectories. Incontrast, decision-making will show little change across all trajectories, consistent with itshypothesized role as an antecedent, rather than a consequence, of cannabis addiction.Understanding more about the links between neuropsychological functions and cannabisaddiction will help clarify theoretical models pertaining to their temporal association. Clinically,knowing more about neuropsychological predictors and sequelae of addiction will help us todevelop more targeted and tailored interventions and prevention programs, consistent withNIDA's goals. Importantly, our findings will clarify whether decision-making is an antecedent riskfactor for cannabis use and addiction, a consequence of use, or both.