Examining bidirectional associations between cannabis use and internalizing symptoms among high-risk emerging adults: A prospective cohort study

Purpose: The co-occurrence of cannabis use and internalizing problems, such as depression and anxiety, during emerging adulthood (18-25 years) is well documented, but the directionality is unclear. This study investigates the bidirectional longitudinal relationships between cannabis use (frequency and consequences) and internalizing problems (depressive and anxiety symptoms) among high-risk emerging adults. Methods: Data came from 7 assessment waves collected over a 2-year period among 900 (56% female) high-risk emerging adults participating in two longitudinal cohorts (Ontario, Canada; Tennessee, USA). Latent curve models with structured residuals were used to explore bidirectional between- and within-person relationships between cannabis-related variables and internalizing problems. Results: At baseline, higher cannabis use frequency and consequences were both associated with higher internalizing symptoms. In between-person models, both cannabis-related factors (frequency and consequences) and internalizing symptoms (depressive and anxiety symptoms) decreased across emerging adulthood. In within-person models, bidirectional relationships were observed (partially supporting both symptom-driven and substance-induced pathways), but cannabis consequences, rather than frequency, were most consistently related to subsequently higher internalizing problems (particularly depressive symptoms). These bidirectional relationships were more pronounced among females and those surpassing clinical thresholds for internalizing problems at baseline. Conclusions: This study found evidence of bidirectional relationships between cannabis involvement and internalizing problems across emerging adulthood, although the prevailing direction was from negative cannabis consequences to increases in internalizing. These findings highlight the importance of cannabis intervention in emerging adults, both to reduce consequences and prevent internalizing symptoms, especially targeting females and those with clinically elevated internalizing problems.