Illegal cannabis has led to a cascade of health and social harms that could potentially be addressed through legalisation, an expert panel has found - but whether that would transpire is unknown.
It also says that getting the regulatory framework wrong and allowing big business to take over could exacerbate the social inequities the current system enables.
The panel, led by the Prime Minister's chief science advisor Juliet Gerrard, released its work this morning to help inform the public debate in the lead up to the referendum in September. The work has been peer-reviewed nationally and internationally.
The referendum, which is part of the Labour-Greens confidence and supply agreement, is about legalising cannabis for recreational use.
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The illegal status of cannabis is meant to deter its use, but the panel says this isn't working because most Kiwis have used it, 15 per cent of New Zealanders have used it in the past year - increasing to 29 per cent for those aged 15 to 24 - and a third of those who use it do so at least once a week.
Nor is criminal punishment much of a deterrence - 95 per cent of users "either continue or increase their cannabis use after arrest or conviction".
And the current "systemic racism" status quo disproportionately affects Māori, the young, and the male.
"Cannabis being illegal isn't stopping people using it and, as a result, society experiences substantial social and health harms related to cannabis," the panel says.
The panel compares the proposed legal framework with the status quo; looks at what has happened overseas where cannabis has been legalised; dives into how it can be harmful; and considers how legalisation might increase health services.
The panel says that harm exists regardless of its legal status, and legalisation has "the potential to undercut the illegal market for cannabis, help reduce cannabis-related harm through regulated product safety, better facilitate intervention and treatment services, and separate access to cannabis from the illegal market for more harmful drugs".
"Whether this plays out in reality is yet to be determined, as legalisation reforms in other places have not been in place for long enough for a full evaluation of long-term impacts."
Overseas data also needed to be interpreted with caution because each jurisdiction has its own unique regulatory framework.
Broadly speaking, use among adults overseas has increased moderately in the short-term, and there is no clear impact on groups that are most susceptible to harm: heavy users or young people, it says.
The panel includes Professor Tracey McIntosh (co-chair, Auckland University), Professor Joseph Boden (Otago University), Professor Benedikt Fisher (Auckland University), Dr Hinemoa Elder (Auckland University), Professor Michelle Glass (Otago University), Associate Professor David Newcombe (Auckland University), Associate Professor Khylee Quince (AUT), Associate Professor Tamasailau Suaalii-Sauni (Auckland University), Professor Doug Sellman (Otago University) and Associate Professor Chris Wilkins (Massey University).
Recap: The proposed legal framework
The framework is outlined in the Cannabis Legislation and Control Bill, which Parliament is expected to progress in the event of a 'yes' vote in September.
"It is not clear how rates of cannabis use would change if recreational use is legalised but it is reasonable to expect that legalisation will 'normalise' cannabis use in society," the panel says.
Among the proposed controls are a purchase age of 20, a ban on public consumption, advertising and online sales, and a daily purchase limit of 14g of dry leaves a day - or the equivalent of about 30 joints.
Cannabis use would only be allowed at home or in specialised cafes, where products in plain packaging and with health warnings could be bought.
Pricing cannabis correctly would be critical, the panel says, as too low a price could increase use and too high a price would draw few people from the black market to regulated legal products.
The bill would place a 15 per cent limit on THC, the psychoactive component of cannabis, for dried plant material. Limits on other products are yet to be determined, but a balance must also be struck: too low a limit could see users shunning legal products.
"Stronger cannabis could still be grown through home-grow provisions in the law."
What are the health harms?
"Illegal cannabis use is common and the majority of people who use cannabis have not experienced harms from their use," the panel says.
It is "generally accepted" that cannabis is less harmful than alcohol or tobacco.
The harms are broadly called "cannabis use disorder", which can manifest as anxiety, sleeping problems and depression.
"People who use cannabis have a one in five risk of developing cannabis use disorder, with risk increasing for those who use cannabis early, often, and use more potent cannabis."
Around one in 10 people who started using cannabis before they are 15 will go on to develop psychosis by age 26.
Risks are greater for pregnant women, and for people with a family history of psychosis, substance abuse or heart problems.
There is also a weak association between cannabis use and depression.
The panel found little to no evidence of cannabis as a gateway drug, and legalisation could even reduce a person's exposure to other illicit drugs.
"Cannabis use has health impacts regardless of whether it is legal or illegal, but the impacts may change depending on how the legal market is regulated," the panel says.
Social harms, the status quo, and 'systemic racism'
The panel says these harms are not just about being locked up. Being prosecuted can lead to life-long stigma, which can lead to reduced job prospects, difficulty in finding housing, or missing out on an education.
Māori are three times more likely to be arrested and convicted of a cannabis-related crime than non-Māori, the panel says.
It is estimated that legalising cannabis could reduce Māori cannabis convictions by up to 1279 per year.
"Systemic racism in the justice system means that Māori are disproportionately more likely to be arrested, sentenced and convicted for drug offences, including cannabis-related crimes."
This exacerbates inequality and social problems: "Criminalisation of cannabis use may cause more harm than cannabis use itself."
"Legalisation has the potential to formally address some of the bias in the justice system by placing Māori on a substantively equal footing with other citizens regarding cannabis use."
Legalising cannabis could help deprived communities whose incomes rely on the black market; the bill includes a "social equity" clause that would see the national production cap shared fairly.
The panel also says that allowing big businesses to dominate the legal market could exacerbate social inequity.
To counter this, the bill includes a clause so that one business would not be able to contribute more than 20 per cent of the national supply.
More health services - maybe
The panel says that problematic users don't seek help out of fear of judgment or arrest, nor is there enough help available.
In 2012/13, one in 100 cannabis users had received help in the last year, and one in 25 people who wanted help did not get it.
"There is currently no or very minimal resource for treatment of cannabis-related harms, especially for young people, and availability of treatment for people with cannabis use disorder varies widely across the country."
Legalisation could reduce stigma or fear of prosecution, the panel says.
"If legal, more people may seek help and more help could be available."
Funding for treatment services could come from cannabis taxes, as well as from money redirected from enforcement.
"Spending on enforcement currently outweighs spending on harm reduction."
Gerrard told the Herald that the panel did not look at how much funding could be redirected.
"It's absolutely clear it's much easier to provide health and social support for
legal drugs than illegal ones.
"People are much more likely to seek help if cannabis is legal, presuming that health and social services are made available - and that could reduce harm."
Overseas evidence: More adult use, little change to youth or daily use
The panel found that legalisation overseas was too recent to draw firm conclusions, and data could be misleading as people may be more likely to report their use.
"It is too early to tell what the impact of legalisation on use rates will be, and we are unlikely to know long-term outcomes on patterns of use for some time," the panel says.
The short-term trends include a moderate increase in adult use, and no clear change in use patterns among groups that are most susceptible to harm: young users and heavy users.
The proposed framework for New Zealand is similar to what exists in Canada, tighter than US jurisdictions, and looser than state-controlled Uruguay.
The short-term trends include:
• A moderate increase in occasional adult use in Canada: "Two per cent more people used cannabis in the past three months, mainly among males, adults over 25 and those from certain regions."
• US studies also showed small increases - 1 to 5 per cent - in past-year use, particularly among college students and people older than 25.
• Between 2011 and 2014 in Uruguay, there was a 1 per cent increase in past-year use and a 1.6 per cent increase in past-month use, but this may be a continuation of a pre-existing trend.
• There are different patterns of problematic use, including a small increase in cannabis harm - 0.9 per cent to 1.23 per cent - in the US for those over 26. An increase in daily or almost daily use in Canada, however, has only occurred in those over 65.
• There is no clear change in use among young people. Studies in the US have shown increases and decreases of around 2 to 4 per cent, or no change, depending on who is surveyed and in which states. In Canada, there has been no reported change in those aged 15-24 for occasional or frequent use. In Uruguay, cannabis legalisation has not appeared to affect youth use.
In US states where cannabis is legal, there has been an increase in the number of children who accidentally ate products containing cannabis, sometimes leading to hospitalisation.
Early evidence from the US also showed more ED visits for cannabis-related reasons, and since legalisation, there has been a 67 to 77 per cent increase in reports of cannabis exposure to the US National Poison Data System.
"No significant burden on the healthcare system has been reported elsewhere, suggesting that any changes are small," the panel says.
There is also limited data on cannabis-influenced traffic fatalities overseas.
Cannabis-impaired driving is not part of the bill, but is included in wider drugged-driving work that the Government is looking at.
Gerrard: The known harms versus the unknown harms
Gerrard told the Herald the overseas data from Canada was promising.
"The fact there hasn't been major changes for youth use or at risk groups is promising. The over 65s are the least at risk. The younger you start to use, the more risk."
She said the social experts on the panel thought that legalisation could be effective in reducing the consequences of systemic racism in the justice system.
"Certainly the social justice experts on the panel think [the proposed legal framework] would make a big difference to those communities."
She said people often had a kneejerk reaction when thinking about the referendum.
"They think, 'It does harm. Why would you legalise?' But there's plenty of harm happening at the moment."
The key question is the harm it might do and whether that harm increases or decreases in a legalised framework compared to the status quo.
On that, Gerrard stuck to the panel's remit and remained steadfastly silent.
"We're pretty sure of the situation at the moment. We're much less sure of what will happen if we legalise it."