Parent and Peer Influences and Longitudinal Trajectories of Cannabis Use from Adolescence to Young Adulthood

Positive parent and peer influences are frequently targets for enhancing prevention and intervention programs for adolescent substance use. However, differences in the patterns of cannabis use trajectories in the transition from late adolescence to young adulthood may affect the quality of relationships with parents and peers. We examined how parent and peer influences in adolescence and in young adulthood relate to cannabis use trajectory groups that distinguish high risk trajectories of cannabis use across ten years; namely, Increasers (20%) and Chronic users (11%), from lower risk user groups of Abstainers (29%), Occasional users (27%), and Decreasers (14%). We assessed mother and father communication and parent monitoring, and as well as experiences of peer victimization and engagement with peers involved in positive and negative activities. Data were from the Victoria Healthy Youth Survey (V-HYS). Youth were randomly recruited in 2003 (N = 662; 48% male; Mage = 15.5) and followed biennially for ten years to 2013 (N = 478; 45% male; Mage = 25.8). Parent monitoring distinguished groups in adolescence, but, as expected, monitoring was low and not significant in young adulthood. Levels of parent communication were high across both age groups, but were not related to the cannabis trajectory groups. Peer influences were similar in adolescence and young adulthood, in showing that deviant peer influences remain greater in high risk user groups across this transition. Implications for preventive and treatment interventions for high risk users in young adulthood are discussed.