From puff, puff, pass, to passing altogether, more young people are staying away from cannabis, with research showing the proportion of teens using the drug each week halving in a decade.
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But it remains unclear whether that's a conscious, sensible decision or because teens are going out less, partying less, and so - the opportunities to try the drug simply aren't there.
"The big factors do seem to be changes in parenting, changes in young people's unsupervised time, and attitude change among young people," Jude Ball said.
Jude Ball Photo: Supplied
Ms Ball, who is the lead researcher and Otago University doctoral candidate, is trying to find out what is behind the decline in risky behaviour among young people.
Those changes meant it was unclear whether young people were choosing not to smoke weed, or were so busy, and persistently supervised that they could not.
"The opportunities for cannabis use will often come up in a social situation where young people might be drinking or smoking - a joint gets passed around," she said.
"So if there are fewer drinking occasions then it stands to reason there are fewer opportunities to try cannabis," she said.
The research shows weekly cannabis use among teens halving from 6.7 percent in 2001 to 3.2 percent in 2012.
The trend closely follows smoking and binge drinking rates, Ms Ball said.
A co-author on the paper, Auckland University associate professor Terryann Clark (Ngāpuhi), said the biggest declines in use were among Māori and poorer young people who were disproportionately affected when they get caught.
"One of the most significant harms from cannabis is around criminalisation. So it's the young person who's getting kicked out of school, it's the young person who's getting in trouble with the police for using cannabis. Actually, those things are far more impactful on young people's long-term outcomes," she said.
A referendum on the legalisation of cannabis would be held at next year's general election.
Drug Foundation executive director Ross Bell said this study relied on old data, and fresh research was needed.
"What this highlights is a massive gap in data and information about drug use in New Zealand. We have talked to government about this for the last few years, particularly in the lead up to the referendum. If New Zealanders do vote for cannabis regulation next year, then we have to have good data now to be able to monitor any changes and trends," he said.
Cannabis could harm young, developing brains, leading to health and social problems later in life, Mr Bell said.
Ms Clark said she was now starting work on the latest Youth Health survey - and hoped that would show a continued decline in use among young people.