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OPINIONSocietyOctober 14, 2020

Cannabis is linked to a greater risk of schizophrenia. Why isn’t that part of the legalisation debate?

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We’ve heard a lot about the social benefits a law change would bring, but precious little on the mental health risks it could also pose, writes Sophie Vreeburg.

Read a response to this column by psychopharmacologist Suresh Muthukumaraswamy here.

Editor’s note: An earlier version of this article made the claim that cannabis can cause schizophrenia. Cannabis has not been proven to cause schizophrenia; rather, there is evidence of a link between some types of heavy usage and a higher risk of developing schizophrenia. The Spinoff regrets the error.

Like every New Zealander who is enrolled to vote, several weeks ago I received an Electoral Commission envelope in the mail. In it was a letter asking me if my enrolment details were correct, some general guidance on voting, and two brochures: one on the End of Life Choice Referendum and the other on the Cannabis Legislation and Control Referendum.

For many, a quick flick through these brochures could be the extent of their research on the proposed changes to cannabis law; others may have delved further into the pros and cons of legalisation on sites such as The Spinoff. Still, no matter how much attention a voter has paid to the issue, it’s likely they’ve seen no mention at all of one incredibly important factor: the link between cannabis and schizophrenia.

Schizophrenia is a form of psychotic illness which affects the way we think. It is characterised by a loss or re-interpretation of reality through delusions, hallucinations, and other bizarre thinking. Episodes of the illness are referred to as psychosis. Research shows a significant connection between schizophrenia and Tetrahydrocannabinol (THC), the chemical component responsible for cannabis’s psychological effects. This form of schizophrenia is also known as cannabis-induced psychosis.

There is no evidence that cannabis can cause schizophrenia. There is, however, significant evidence that, in some situations, heavy use of high potency cannabis can increase the risk of developing schizophrenia.

According to Robin Murray, professor of psychiatric research at the Institute of Psychiatry at London’s Kings College, the risk of schizophrenia increases with the potency of the cannabis used: “if the risk of schizophrenia for the general population is about 1%, the evidence is that, if you take ordinary cannabis, it is 2%; if you smoke regularly you might push it up to 4%; and if you smoke ‘skunk’ (high-strength cannabis) every day you push it up to 8%”. Evidence shows the risk is concentrated in users of high strength cannabis in adolescence; it should be noted here that the proposed law would set an age limit of 20 to use or purchase cannabis.

Auckland University psychiatry professor Graham Mellsop has further found that the proportion of patients diagnosed with schizophrenia is significantly higher in instances of prolonged illicit substance abuse than in prolonged alcohol abuse.

So why are the links between cannabis and schizophrenia not a greater talking point in this referendum?

One of the most significant factors in favour of legalisation is the criminalisation of Māori, particularly rangatahi (youth), as a result of cannabis possession. Studies show that Māori are 1.8 times more likely than non-Māori to face legal consequences of their cannabis use. While legalisation would reduce the criminalisation of Māori, it should be noted that Māori would still be at a significantly increased risk of developing cannabis-induced psychosis or schizophrenia due to high rates of usage among Māori.

If the referendum passes, the resulting legislation will establish a Cannabis Regulatory Authority that will in turn set limits on THC. We already know that the strength of cannabis available in New Zealand has increased significantly over the last 30 years. Remember those figures from Robin Murray – that 8% of users of high-potency cannabis (or around 8000 out of every 100,000) will develop schizophrenia? In an email to me, Brendan Kelly, professor of psychiatry at Trinity College in Dublin, made an important point: all 100,000 of those users are at risk:

“Yes, 8,000 of them will actually develop schizophrenia, but the problem is, it is not possible to pick out which 8,000 that will be. So, all are at risk. [High strength] cannabis multiplies the risk of schizophrenia eight-fold. That is a huge multiplication of risk.”

Commercial pressure not only spurs widespread accessibility of cannabis but can also pressure producers into developing strains with an ever-higher THC content. The UK in particular has had considerable issues with “skunk” cannabis, which naturally contain higher levels of THC. This high-potency cannabis contains approximately 14% THC.

In New Zealand, there is evidence that high potency cannabis use increases the rate of schizophrenia in those genetically predisposed to its onset by approximately five or six times compared to non-users. At this stage, the government has suggested unadulterated cannabis available for commercial sale would have an initial maximum potency of 15% THC – higher than the potency shown to increase the risk of schizophrenia in UK users. Evidently, this presents a significant risk to uninformed users and to those genetically predisposed to schizophrenia.

The significance of this medical evidence can be boiled down to one simple principle: informed consent. Just as those who are being treated in the healthcare system have the right to give informed consent, those who are voting in the referendum are entitled to be informed of the link between cannabis and schizophrenia.

It is evident voters are currently not adequately informed. Not only is there no reference to the link between cannabis and schizophrenia in the referendum material recently mailed to New Zealand voters, the public debate has tended to gloss over the health risks of cannabis in favour of the social benefits of legalisation. At the same time, it is unlikely that many people will read through all 65 pages of the bill to understand the full extent of the legalisation before they vote yes or no. So can they say they are truly giving informed consent?

Under the proposed law, a cannabis product label would have to include the amount of THC it contained. While that information is valuable, it’s largely ineffective if users are unaware of the psychiatric effects of particular levels of THC. Should cannabis be legalised as a result of the referendum, the government must acknowledge there is a risk that some users may develop cannabis-induced psychosis, and that the risk is particularly acute for those users who are ill-informed about the effects of THC or who have a genetic predisposition to schizophrenia. Just as cigarette packets carry graphic warnings of the effects of smoking, cannabis users should have the right to know that “cannabis use can increase the risk of schizophrenia”.

Sophie Vreeburg is a fourth year law student at the University of Auckland, the co-director of the Equal Justice Project and a student representative on the Auckland District Law Society Mental Health and Disability Committee. She is passionate about mental health advocacy and issues surrounding access to justice. 

Anthony Rogers assisted in the editing of this article. He is a senior barrister and former member of the Auckland District Law Society Mental Health and Disability Committee who specialises in criminal law, traffic accident prosecutions, parole hearings and Mental Health Act applications. He has extensive experience working with clients exposed to the psychiatric effects of cannabis consumption.

Read more: Everything you need to know about the 2020 cannabis referendum

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Associate health minister Jenny Salesa, National Party health spokesperson Dr Shane Reti and Jacinda Ardern are all promising to address the health inequities faced by many in South Auckland (Image: Tina Tiller)
Associate health minister Jenny Salesa, National Party health spokesperson Dr Shane Reti and Jacinda Ardern are all promising to address the health inequities faced by many in South Auckland (Image: Tina Tiller)

PoliticsOctober 13, 2020

Finding a remedy for South Auckland’s health issues

Associate health minister Jenny Salesa, National Party health spokesperson Dr Shane Reti and Jacinda Ardern are all promising to address the health inequities faced by many in South Auckland (Image: Tina Tiller)
Associate health minister Jenny Salesa, National Party health spokesperson Dr Shane Reti and Jacinda Ardern are all promising to address the health inequities faced by many in South Auckland (Image: Tina Tiller)

Covid has highlighted South Auckland’s potential vulnerability to a health crisis, so what are our politicians promising to do about the region’s ongoing problems?

Updated with statistics minister James Shaw’s comments.

Mary* is a GP in South Auckland. 

She’s on the frontline, helping those with often complex health issues in one of New Zealand’s most vulnerable regions, and she is growing more and more frustrated with the support for her patients from Counties Manukau DHB, particularly through Middlemore Hospital.

“There are so many examples of people falling through the gaps and it’s because they are probably overworked in the hospital,” says Mary. “It seems we’re just providing band aid solutions – and we’re not fixing the root causes of the issue. I have no idea what kind of wrap-around service they have there, but there seems to be a disconnect between us and the hospital.”

She raises a number of examples, including a situation where a patient needed to be tested for cancer but due to delays he had to wait 13 days for a diagnosis after the initial appointment. She says this delay may have resulted in the cancer getting worse. 

“He wasn’t really listened to,” she says. “He had delays in getting extra scans, delays in getting his case reviewed and then the specialists were delayed. It’s unacceptable in the sense that there was a high chance he had cancer, and this is an aggressive cancer – if he had been diagnosed within the first week, would it have progressed as much? That’s a question we just don’t know the answer to.”

She gives another example of a patient whose heart issues were not picked up early enough and as a result, treating him is proving difficult. She says communication breakdown is often part of the problem. 

“The language barrier is a huge thing,” she says. 

“A lot of diagnoses come from understanding family history – so if you don’t have an interpreter there, you’re not going to fill in the gaps and it’s going to be incorrect and it’s just too simplistic to blame the individual.”

Steve* is another South Auckland-based GP, who has also worked at Middlemore, and he shares Mary’s concerns.  

“There was a Pacific support team who would provide Pacific patients with support and help navigating the hospital system – but apparently the service was downsized. In an environment where people are unwell and suffering and the way things work are unfamiliar or even hostile, this was extremely disappointing from a clinical perspective, considering how important that support is for patients getting the best health outcomes from their stay in hospital.”

He believes the DHB is being forced into choosing between clinical services and the wrap-around support that can ensure clinical services are more effective. 

“It kind of showed that when the financial shove comes, it’s some of the less clinical services that get pushed out, but this support service is arguably one of the most important with regards to how the hospital engages with Pacific patients.”

As pointed out by Counties Manukau Health’s director of population health Dr Gary Jackson in an earlier interview on this subject, census undercounts of South Auckland’s Pacific population are resulting in the DHB missing out on much-needed operational funding. 

“It’s incredibly frustrating,” he said in our previous article. “We’re a DHB which is dealing with the largest number of Pasifika people, the second-largest number of Māori people, the highest number of people living in the most deprived areas, and yet we’re the DHB that’s getting penalised by the population count. We do a reasonable job at being efficient at allocating money, but we’re going to be running a $30 million deficit this year, which is essentially this [missing] money.”

So how will the next government deal with the inequities being experienced by those in South Auckland? 

National Party health spokesperson and Whangārei electorate MP Dr Shane Reti says it starts by ensuring the next census isn’t botched like the last one.  

“It just seems like they [the government] were distracted, they took their eye off the ball … they didn’t follow the methodology, and they were late to react when they realised it wasn’t working, but the implications of this are wide ranging. Northland, for example, doesn’t get the health funding that it truly should have. The census is a baseline for so much government funding that if you get that wrong, you fundamentally miss out on funding. 

“[For Census 2023] I would be making sure we wouldn’t be making the same mistakes as the 2018 census. We would project manage this more closely, monitor it more closely, and react more quickly and have other portfolio holders keeping an eye on it.”

To address inequities, National is also promising to fund a “primary-care navigator” for every general practice to boost frontline health services’ capacity and require DHBs to annually report against a Māori health strategy.

Labour Party leader Jacinda Ardern says, if re-elected, her party will deal with how DHBs are funded, taking into account regions with high levels of deprivation. 

“I haven’t received anything specific to the information that Counties Manukau has raised,” she says. 

“But more generally when it comes to health funding, we have had an ambition and a concern that currently the way we calculate the support for our DHBs is often very heavily weighted on population growth and it doesn’t necessarily take into account some of those health disparities. So in the work we are doing around health sector reform, that is something I hope we will be able to address.”

Labour’s Jenny Salesa is the associate health minister and electorate MP where Middlemore Hospital is located. She says part of her government’s efforts is the $17 million Ola Manuia: Pacific Health and Wellbeing Action Plan 2020-2025, announced earlier this year, which aims to develop new and innovative methods to improve Pacific health. 

“Population-based funding is not an issue that has arisen just over the last three years,” she says. 

“Improving the health and wellbeing of all Pacific people in New Zealand has been a priority of mine, and of this government. Alongside [Ola Manuia], inequalities and funding distribution will be considered during the implementation of the Simpson report into the health and disability sector.”

Auckland councillor and Ōtara Health chairperson Fa’anana Efeso Collins with Auckland mayor Phil Goff (Photo: Todd Niall/RNZ)

And when it comes to the next census in 2023, statistics minister James Shaw says there will will be better, more targeted engagement with population groups that were undercounted in the 2018 Census.

Stats NZ has $210 million available to run the 2023 Census – a two thirds increase on the total cost of the 2018 Census,” he says. “This funding boost means there will be more boots on the ground for the census operation and more paper based forms available from the outset. On top of this, Stats NZ is working hard to design and execute targeted engagement strategies with communities, including the Pacific community, and the South Auckland community.”

This extra funding will also go towards implementation of a Pacific engagement strategy and see a 150% increase in door-knocking staff.

Auckland councillor Fa’anana Efeso Collins is also the chairperson of Ōtara Health, which has been helping run a food bank and testing station over the last six months. He says while South Aucklanders might feel a little bit cynical about the different proposals being suggested to turn around the region’s dire health statistics, he believes Covid has highlighted ways the region is also starting to take a greater lead in resolving its own issues. 

“What this year has shown us is that our Pacific community and South Aucklanders in general are able to step up time and time again,” he says. “Our people got tested in large numbers and so many of our local organisations mobilised to provide food support during the two lockdowns. I think we can see there’s a growing community resilience that hopefully can translate into ensuring better health outcomes for our community into the future.”

Comment was sought from the Counties Manukau District Health Board, but a spokesperson said the DHB did not wish to comment at this time. 

*Mary and Steve are not the real names of the doctors mentioned in this article.