Aims To examine the relationship between cannabis use in adolescence/young adulthood and levels of educational attainment.
Design Data were gathered over the course of a 25-year longitudinal study of a birth cohort of 1265 New Zealand children.
Measurements Measures analysed included (a) frequency of cannabis use in adolescence and young adulthood (15–25 years); (b) levels of educational achievement to age 25 years; and (c) social, family and individual characteristics assessed prior to age 16.
Findings Increasing cannabis use was associated with increasing risks of leaving school without qualifications, failure to enter university and failure to obtain a university degree. The association between cannabis use and leaving school without qualifications persisted after control for confounding factors. When due allowance was made for pre-existing levels of cannabis use there was no evidence to suggest the presence of reverse causal pathways in which lower educational achievement led to increased cannabis use.
Conclusions Findings support the view that cannabis use may act to decrease educational achievement in young people. It is likely that this reflects the effects of the social context within which cannabis is used rather than any direct effect of cannabis on cognitive ability or motivation.