PROJECT SUMMARY/ABSTRACT Among the physiological systems most important to brain development in emerging adulthood is the endocannabinoid system, which among other roles facilitates cognitive and behavioral processing, including the underpinnings of stress management and resiliency. Sex differences in endocannabinoid system development have been identified, and emerging evidence indicates a bidirectional relationship between stress exposure and the endocannabinoid system during emerging adulthood. Repeated exposure to exogenous cannabinoids, such as those administered via cannabis use, perturbates endocannabinoid system development, which may adversely affect the programming of future coping in a manner that differs by sex. Use of cannabis, which exerts its psychoactive effects via delta-9-tetrahydrocannabinol binding to endocannabinoid receptors, is more common among emerging adults than in any other age group. Many regular users develop a maladaptive, impairing pattern of use characterized as cannabis use disorder (CUD). A constellation of preliminary evidence suggests several factors disproportionately complicate CUD in females compared to males; the salience of these factors in emerging adulthood indicates that this developmental stage deserves focused sex differences research to inform clinical management. A central running thread is the importance of stress and stress-reactivity across endocannabinoid system development, cannabis use, CUD, cannabis withdrawal, and relapse to cannabis use. We propose an experiment that combines rigorous ecological momentary assessment (EMA), controlled human laboratory procedures, and innovative bioassay collection. Emerging adult cannabis users with CUD (ages 18- 25, N=148, 1:1 female to male ratio) will undergo 3 days of reinforced abstinence with EMA monitoring of cannabis withdrawal and stress-related symptoms, followed by a standardized laboratory stress induction paradigm. Blood levels of endocannabinoid system markers will be assessed before and after the abstinence period; during the lab session, self-report measures and biomarkers of stress reactivity will be collected. Double- blind cannabidiol (CBD) versus placebo dosing before the laboratory stress paradigm will allow for examination of effects on stress response during withdrawal. Prior work indicates CBD administration reduces stress response in general populations and preliminary research suggests this effect may extend to cannabis users; this has not been rigorously applied to induced stress amid cannabis withdrawal in emerging adults with CUD, a context particularly important for females with CUD who often report using cannabis to cope with stress. Following the laboratory session, EMA monitoring will resume as participants return to ad libitum cannabis use, providing the opportunity to test associations between stress reactivity and time to resumption of use. The proposed study is designed to elucidate sex differences and guide the developm...