Early onset cannabis use and psychosocial adjustment in young adults.

The relationships between early onset (prior to 16 years) cannabis use and later psychosocial adjustment was examined in a birth cohort of New Zealand children studied to age 18 years. Early onset users had significantly higher rates of later substance use, juvenile offending, mental health problems, unemployment and school dropout. The linkages between early onset cannabis use and later outcomes were largely explained by two routes that linked cannabis use to later adjustment. First, those electing to use cannabis were a high risk population characterized by social disadvantage, childhood adversity, early onset behavioural difficulties and adverse peer affiliations. Secondly, early onset cannabis use was associated with subsequent affiliations with delinquent and substance using peers, moving away from home and dropping out of education with these factors in turn, being associated with increased psychosocial risk. The implications of these results are examined.