Drug-control policy in New Zealand can be simplified into a tale of two campaigns.
The first, New Zealand's campaign against tobacco, roared into life in 1984. Thirty-two per cent of Kiwis smoked at the time, leading to some of the highest cancer rates in the world. This was a catastrophe in slow motion.
An immense public education programme was implemented, a tax on tobacco products was introduced and stronger health warnings were prominently displayed on cigarette packs.
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Within a decade, a ban on selling tobacco to Kiwis under 16, and later 18, was introduced. Previously inescapable tobacco advertising was dramatically restricted. And it worked.
Between 1985 and 1990, tobacco use declined faster in New Zealand than anywhere else in the developed world. By 2000, just 25 per cent of Kiwis regularly smoked. By 2018, that number had dropped further to 13 per cent. In other words, over the past four decades New Zealand has consistently won against the Big Tobacco goliath.
The second campaign, our fight against cannabis, began in 1975. That year, to great fanfare, the Misuse of Drugs Act introduced harsh fines and jail time for cannabis possession and use.
Since then, the government has spent unfathomably large amounts to enforce these laws - the NZ Institute of Economic Research used government data in 2016 to show that it cost $180 million to enforce our criminalisation of cannabis each year. That doesn't include the social toll of voluntarily forcing tens of thousands of Kiwis through our criminal system for minor offences - simultaneously traumatising them and pushing them onto a path they will find difficult to escape.
Meanwhile, the people profiting are the gangs who are growing and selling the crop.
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And it has failed. Evidence from the Christchurch Health and Development Study shows that almost 80 per cent of Kiwis will try cannabis before their 25th birthday. That's one of the highest rates in the developed world. In fact, data from the Ministry of Health shows that the number of Kiwis who have recently used cannabis is actually growing - fast.
In 2011, just 8 per cent of Kiwi adults would admit to having used cannabis within the last 12 months. In 2018, that had almost doubled to 15 per cent.
Either the number of Kiwis using cannabis recently really is growing, or the anti-cannabis campaign has failed so spectacularly that twice as many Kiwis felt comfortable admitting their use to a government agency. Neither is a sign of success.
Simply put: the campaign against tobacco is working. The campaign against weed isn't. And that's despite the fact that nicotine is more addictive and tobacco more toxic than cannabis.
The lesson to draw here is simple: we can only control cannabis if we can regulate it, and we can only regulate it if it is legal.
There's been plenty of concern that voting yes in the 2020 referendum on cannabis legalisation might lead to a surge in the number of Kiwis using cannabis, and in particular, young Kiwis.
Thankfully, New Zealand isn't the only country in the world considering changing its approach - we can learn from others' experiences.
The most authoritative information on youth cannabis use comes from a 2019 meta-analysis of 1.4 million American teenagers. That analysis showed that in states where recreational cannabis has been legalised, young people are now 8 per cent less likely to try cannabis and 9 per cent less likely to use it frequently. These are incredibly significant victories, and consistent with previous studies.
Why did youth cannabis use go down after legalisation? It's likely a combination of factors: dispensaries won't sell to underage customers for fear of losing their license, gangs are pushed out of the market because it's easier and more profitable to sell legally, cannabis loses some of the cultural edge once it's taken out of the dark and it becomes less appealing once we can talk about it honestly and without fear.
None of this should be a surprise. While the fight against cannabis has ineffectively struggled on, we've championed the health approach to drug control with our campaign against tobacco.
For four straight decades we've been able to steadily whittle down the number of people using it, saving and prolonging hundreds of thousands of lives in the process, all while allowing it to remain legal.
In 2020, Kiwis will have to choose: continue to fight an unwinnable war, or change strategies and turn the tide. I hope we choose the latter.
• Pete McKenzie is a journalist and researcher focused on youth, foreign affairs and health. Follow him on Twitter at @PeterTMcKenzie