Early cannabis use may affect academic achievement

A new collaborative study of more than 6000 New Zealanders and Australians found those who used cannabis before the age of 18 ended up with fewer academic qualifications.

The research was based on the combined findings of three studies, including the University of Otago’s long-running Christchurch Health and Development Study.

The other studies were the Victorian Adolescent Health Cohort Study and the Mater University of Queensland Study of Pregnancy.

All studies tracked young people throughout adolescence and young adulthood.

Researchers found young people who used cannabis before age 18 were more likely to fail to complete high school; less likely to enter university and less likely to attain a university degree.

Early users of cannabis were less likely to achieve academically, even when other factors such as socio-economic status, previous educational achievement and other personal factors were taken into account.

People who used cannabis before age 15 were the most likely to not graduate from high school, not attend university or fail to get a degree.

The findings also suggest that the early use of cannabis has a somewhat greater effect on the educational achievement of males than females. This was particularly evident for university entrance.

Christchurch Health and Development Study director Professor David Fergusson says the research shows a robust association between the early use of cannabis and educational under-achievement.

Possible reasons for this robust association may be that early use of cannabis sets in train biological, individual or social processes which affect the young people’s motivation, learning or commitment to education, Fergusson says.

This research – the first from this consortium of three longitudinal studies - adds to a growing body of evidence linking early cannabis use with multiple adverse outcomes, including educational under-achievement.

Other negative outcomes associated with early cannabis use are mental health problems, driving impairment and increased use of other illicit drugs.

All three longitudinal studies are part of the Cannabis Cohort Consortium convened by the National Drug and Alcohol Research Centre at the University of New South Wales. The Christchurch Health and Development Study is funded by grants from the Health Research Council of New Zealand.