Teenagers who regularly use cannabis before they turn 17 are much more likely to drop out of high school or university, or attempt suicide, than those who never smoked a new study has found.
Australian research by the National Drug and Alcohol Research Centre (NDARC) at the University of New South Wales has been hailed as the best evidence yet of the harms of marijuana during teenage years.
“Our findings are particularly timely given that several US states and countries in Latin America have made moves to decriminalise or legalise cannabis, raising the possibility that the drug might become more accessible to young people,” study author Professor Richard Mattick said.
In the study, Australian and New Zealand researchers combined data on 3,765 participants who used cannabis from three large, long-running studies to look at the link between the frequency of cannabis use before age of 17.
Researchers also looked at seven developmental outcomes up to the age of 30 years, including whether the teenagers completed high school, obtained a university degree, were dependent on cannabis, used other illicit drugs, attempted suicide, suffered depression or were on welfare.
It found teenagers who were daily users of cannabis before age 17 were more than 60 per cent less likely to complete high school or obtain a degree compared to those who had never used the drug.
The large meta-analysis also indicated daily users of cannabis during adolescence were seven times more likely to attempt suicide.
In addition, those teenagers had a chance of cannabis dependence 18 times higher than others, and were eight times more likely to use other illicit drugs later in life.
Associate Professor Simon Denny from the Faculty of Medical and Health Sciences at the University of Auckland said the paper showed increasing frequency of cannabis use also increased the risk of poor outcomes in adulthood.
“This paper provides the best evidence to date on the harms of marijuana use during adolescence as it combines three large longitudinal studies that track the lives of children through to adulthood,” he said.
Cannabis is one of the most widely used illegal drugs with around 1 per cent of 14 to 19 year olds in Australia daily users of the drug, while 4 per cent use it weekly.
Lead author of the study Dr Edmund Silins said the findings are timely.
“Our results provide strong evidence that the prevention or delay of cannabis use is likely to have broad health and social benefits,” Dr Silins said.
“Efforts to reform cannabis legislation should be carefully assessed to ensure they reduce adolescent cannabis use and prevent potentially adverse effects on adolescent development.”
The research was published in The Lancet Psychiatry journal.