Cannabis use among New Zealand high school students has fallen across all socioeconomic and ethnic groups, with the biggest declines seen in Māori, younger students and those in low decile schools, new research shows.
The research by the University of Otago, Wellington shows there has been a long term decline in lifetime cannabis use among high school students, from 38 per cent in 2001, to 23 per cent in 2012.
The proportion of teens who use cannabis weekly, or more often, halved, from 6.7 per cent to 3.2 per cent over the 11-year period.
In contrast, weekly cannabis use in the adult population remained relatively stable, at about five per cent of the population in 1998 and 2007/2008, and just under four per cent in 2012/13, according to Ministry of Health figures.
The new research comes ahead of next year's referendum on legalising personal cannabis use.
Researcher Jude Ball says not only are teenagers less likely to use cannabis, but they're increasingly staying away from alcohol, tobacco and other drugs too.
The proportion of students who reported they had never used other psychoactive drugs increased over the study period from 89 per cent in 2001 to 95 per cent in 2012, she says.
Ms Ball says the decline in drug taking in adolescents is welcome news, with regular cannabis use associated with a range of adverse health impacts, especially in adolescents.
"Early age of initiation (under 16 years of age) particularly in combination with alcohol and/or tobacco use is associated with greater risk of psychosis, addiction, poor educational outcomes and long-term functional impairment, so preventing or delaying cannabis use is important," she says.
Ms Ball also says the decline in cannabis use among teens is surprising "given our increasingly liberal attitudes towards cannabis", but is in line with trends overseas.
"Studies suggest that adolescent cannabis use is influenced by tobacco and alcohol trends, so tighter regulations on tobacco and alcohol use may play a role in mitigating the potential harm of cannabis liberalisation for teenagers."
With New Zealanders to vote on legalising personal cannabis use at the 2020 general election, Ms Ball says it's vital that any law changes minimise the risk of increasing youth cannabis use.
"Despite recent decreases, New Zealand adolescents are still much more likely to smoke cannabis than teens in Australia or England, so there is no room for complacency," she says.
The study is based on an analysis of data from the Youth 2000 National Youth Health and Wellbeing surveys undertaken in 2001, 2007 and 2012 by the Adolescent Health Research Group at the University of Auckland.