Cannabis legalization is expected to result in more frequent and compulsive use, potentially contributing to worsening psychosocial functioning among some cannabis users. This review evaluates associations between cannabis use and psychosocial functioning in recently published reports from prospective longitudinal studies and considers evidence for and against causation. Unlike previous reviews, studies of adolescents/emerging adults are considered separately from studies that followed adolescents well into adulthood, in part because of vast differences in cumulative cannabis exposure. Infrequent adolescent cannabis use is associated with poorer psychosocial functioning in some domains in emerging adulthood, whereas chronic, frequent adult use, regardless of adolescent-onset versus adult-onset, is associated with poorer psychosocial functioning in many domains. Associations are likely attributable to a combination of causal and non-causal mechanisms, with causal mechanisms likely to be social, not neurotoxic, in nature.
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