Whether young people would use more cannabis was a hot topic during a debate tonight on the October 17 referendum to make recreational cannabis legal.
Police Association president Chris Cahill said that education was key to turn young people off cannabis, and it had previously worked to make methamphetamine a "dirty drug" before Government money dried up during the GFC and "we lost a generation".
Drug Foundation executive director Ross Bell said a key part of the controls that legalisation would bring were the hundreds of millions of dollars to be used for education and health services.
But Say Nope To Dope spokesman Aaron Ironside said youth use would rise simply because "it will be everywhere".
He added that it would also be advertised on social media, even though the proposed law explicitly bans advertising.
"The social media world is more agile than we are anticipating. SnapChat images appear and disappear - this is an impossible thing to police."
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Cahill, Bell, Ironside and Associate Professor of Law Khylee Quince debated the merits and demerits of legalisation tonight in a Herald-ZB debate hosted by Newstalk ZB's Heather du Plessis-Allan.
Ironside said a legal market that made it harder for young people to get weed would lead to gangs competing for the youth market.
That would see prices drop, and youth use would rise, he said.
Bell cited the PM's chief science adviser's expert panel, which Quince was a member of, which showed that youth use in Canada had not gone up since legalisation.
Canada legalised two years ago, and since then there's been a moderate increase in occasional adult use, an increase in daily or almost daily use for those over 65, and no reported change in use among those aged 15-24 for occasional or frequent use.
Bell added it was easier to talk to young people about a legal product, and it was easier for them to ask for help if it was legal.
Quince added that being caught with cannabis brought about social harms - such as getting kicked out of school or being unable to find work - that were arguably worse than the health harms.
She cited Ministry of Justice statistics showed 230 people in 2019/20 were convicted for cannabis use/possession alone, and five of them were jailed.
But Cahill said it was "nearly impossible" to get thrown in jail for use/possession of cannabis.
He said most cops were against legalisation because of the harm they've seen, especially in rural, deprived communities.
Bell said cannabis was already here, and it was about how to reduce harm. "We aren't inventing cannabis."