Cannabis use and educational achievement: findings from three Australasian cohort studies.
BACKGROUND
The associations between age of onset of cannabis use and educational achievement were examined using data from three Australasian cohort studies involving over 6000 participants. The research aims were to compare findings across studies and obtain pooled estimates of association using meta-analytic methods.


METHODS
Data on age of onset of cannabis use (<15, 15-17, never before age 18) and three educational outcomes (high school completion, university enrolment, degree attainment) were common to all studies. Each study also assessed a broad range of confounding factors.


RESULTS
There were significant (p<.001) associations between age of onset of cannabis use and all outcomes such that rates of attainment were highest for those who had not used cannabis by age 18 and lowest for those who first used cannabis before age 15. These findings were evident for each study and for the pooled data, and persisted after control for confounding. There was no consistent trend for cannabis use to have greater effect on the academic achievement of males but there was a significant gender by age of onset interaction for university enrolment. This interaction suggested that cannabis use by males had a greater detrimental effect on university participation than for females. Pooled estimates suggested that early use of cannabis may contribute up to 17% of the rate of failure to obtain the educational milestones of high school completion, university enrolment and degree attainment.


CONCLUSIONS
Findings suggest the presence of a robust association between age of onset of cannabis use and subsequent educational achievement.
Horwood
L John
LJ
Christchurch Health and Development Study, Department of Psychological Medicine, University of Otago-Christchurch, Christchurch, New Zealand. john.horwood@otago.ac.nz
Fergusson
David M
DM
Hayatbakhsh
Mohammad R
MR
Najman
Jake M
JM
Coffey
Carolyn
C
Patton
George C
GC
Silins
Edmund
E
Hutchinson
Delyse M
DM
D000328:Adult; D000367:Age Factors; D015331:Cohort Studies; D004522:Educational Status; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology; D009520:New Zealand / Q000453:epidemiology; D012737:Sex Factors; D055815:Young Adult