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Cantabrians in large study on impact of teenage cannabis use

Christchurch campus

Wednesday 10 September 2014 11:13am

Professor D Fergusson
Professor D Fergusson

Teenagers who use cannabis daily are 60 per cent less likely to complete high school or get a degree compared with non-users, latest research shows. The study, published in the latest edition of The Lancet Psychiatry, also shows daily users are nearly seven times more likely to attempt suicide than peers who do not use cannabis.

The study combined data from three large, long-running Australasian studies to examine associations between cannabis use in adolescence and later life outcomes. One of the studies was the University of Otago’s Christchurch Health and Development Study (CHDS).

Researchers, including the CHDS’s Professor David Fergusson, found a strong connection between the extent of use of cannabis before age 17 and a number of outcomes assessed up to the age of 30.

Compared with those who never use cannabis, daily users (aged under 17) were:

  • 60% less likely to complete high school and 60% less likely to attain a university degree qualification
  • 18 times more likely to become cannabis dependent
  • 8 times more likely to use other illicit drugs
  • Nearly 7 times more likely to attempt suicide

The study also found that the risks of these adverse outcomes increased steadily with the amounts of cannabis used, with daily users having higher risks than weekly users and weekly users having high risks than monthly users.

Professor Fergusson says these associations are consistent across studies, and cannot be explained by differences in the family background or childhood experience of cannabis users and non-users.

He says the findings reinforce the message that cannabis use in adolescence, and particularly early onset regular cannabis use, is not without harm. Preventing the onset of cannabis use amongst young people could reduce harm.

Any changes to legislation around cannabis use should be carefully assessed against the potential for increasing the availability and/or use of cannabis to young people, and the likely adverse effects on adolescent development, Professor Fergusson says.

The New Zealand part of the study was funded by the Health Research Council of New Zealand and by a grant from the Australian Government National Health and Medical Research Council.

For further information contact

Professor David Fergusson
Tel 64 3 372 0406
Kim Thomas
Senior Communications Advisor 
Tel 64 27 222 6016

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