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No longer the healthy option

1 Nov 2013
Keri Welham
This article was published 11 years ago. Content may no longer be relevant.

20 years on from the New Zealand Drug Foundation’s first cannabis and health conference, Keri Welham takes a look at Aotearoa’s most widely used illegal drug to see what has changed since 1993.

It is 20 years since Professor Wayne Hall gave his first public lecture on cannabis and health. The platform was the 1993 New Zealand Drug Foundation symposium.

He had been asked to review research on cannabis and health by the Australian government earlier that year, and his presentation focused on mental health. That first lecture, at a concurrent session late on the second day of the symposium, led Hall down a research tangent he’s been following ever since.

This year, the Drug Foundation and leading international researchers will again turn their attention to issues of cannabis and health. And Hall, now a member of the International Narcotics Control Board and a Queensland University professor, will give the keynote address. These days, his expertise extends to various aspects of mental health, cannabis dependence and medicinal cannabis use.

Reflecting on those two decades, Hall says there have been significant shifts.

“The big change is acknowledging people can experience problems with cannabis use. Back then, no one got into trouble with cannabis.”

It was believed cannabis users mostly had jobs, homes, relationships. They were functioning at a higher level than heavy users of alcohol or opiates. However, the view of cannabis as a harmless drug has faded.

“It is quite clear that there are some groups in the community who do experience difficulties,” Hall says. What else have the decades between these symposia revealed? What do we now know that wasn’t known 20 years ago?

Homegrown breakthrough

Let’s go back to 1993. Bill Clinton moves into the White House, Czechoslovakia ceases to exist and the European Union is formally established, actress Audrey Hepburn dies and One Direction singer Niall Horan is born. People wear dreadlocks, waistcoats, berets. Meatloaf wails, “I would do anything for love”, fuel injection becomes a standard feature in the top-selling Ford Escort and, on Coronation Street, brassy Bet Lynch bawls her eyes out when she realises her miserable ex-husband Alec Gilroy has a new love interest.

In some ways, 1993 seems a world away, but many of the issues that were front of mind in drug prevention live on. In 1993, the Drug Foundation symposium featured sessions on cannabis use among Māori and youth, the psychology and educational philosophies of counselling users of cannabis, the drug’s impact on sporting performance, and mental health.

But there were also sessions on music as a healer, motivational interviewing, and the Rastafarian movement and cannabis use in Jamaica.

Agitation for legislative reform cut a backdrop to the 1993 symposium, and it is an even more visible and heated factor of the political landscape today. The same can be said of concern at the impacts of youth cannabis use and high levels of use among Māori. But fear over rising cannabis use, which was a key feature of the landscape 20 years ago, has fallen away as newer, more alarming drugs such as methamphetamine take hold and cannabis use among young New Zealanders drops.

In 1993, a drugs survey from three years earlier was used to gauge cannabis use. It canvassed more than 5,000 New Zealanders, aged 15 to 45, and found 43 percent had tried cannabis, 12 percent had used it within the past year and had not stopped using and 3 percent had used it at least 10 times in the previous 30 days.

Today, a 2010 report is used. It found 14.6 percent of adults, aged 16 to 64, used cannabis in the 12 months leading up to the 2007/8 survey on which the report was based. Meanwhile, the Health and Wellbeing of New Zealand Secondary School Students in 2012 report reveals 38.2 percent of teenagers had tried cannabis in 2001, but this had fallen to 23 percent by 2012.

The Christchurch Health and Development Study found 75 percent of New Zealanders try cannabis by the age of 25. The study tracks 1,265 children born in Christchurch in the winter of 1977. It has been the source of some 400 reports and academic papers, including some focused on cannabis and mental health.

Hall says, thanks to the development study, we now know a lot more about the impacts of regular cannabis use on young adults than we did in 1993 (when the participants were 16). The groundbreaking work of Professor David Fergusson and his team at the University of Otago, Christchurch, has established a link between cannabis use and psychosis symptoms such as paranoia, delusion and perhaps hallucination. The linkage is strongest among users who are both young and report heavy use

This research has offered one of the most pronounced advancements in the understanding of the impacts of cannabis and is supported by the findings of Australian and European research. 

Young people and cannabis

Cannabis remains something of a societal oddity. It is both illegal and commonplace.

Otago University Associate Professor Joseph Boden works on the Christchurch Health and Development Study (CHDS). He finds the drug’s status intriguing: “It’s normal, even in an environment where it’s not legal.”

He says the Otago study shows most Kiwis try cannabis once or twice but never return to the drug. “It doesn’t fit in that well with people’s lifestyles.”

There is no known fatal dose for humans. There is a listed LD50 (lethal dose) for rats, mice and dogs, but it is very large; so large that an analogous dose for humans would be pretty much impossible to consume. Cannabis has been used by humans much longer than the 50-odd years it’s had a profile in the western world.

“Humankind has a very long history with the drug; has had an awareness for a very long time,” Boden says.

That’s perhaps evidenced by the fact humans have THC receptors in the brain. Boden says these ‘set points’ mature or harden in adulthood (sometime around 18–21years). Before the set points mature, heavy cannabis use can cause changes to the brain that make a person more susceptible to some of the adverse effects of cannabis use.

“What we do know is that the dangers of cannabis use are strongest for young users and heavy users.” Heavy use is defined as somewhere between daily and weekly use.

“Young brains are really susceptible to the … effects of the drug.” 

Adopting cannabis culture

Boden says Māori have much higher levels of cannabis consumption and dependence than non-Māori. In the CHDS, Māori at age 25 had nearly twice the rate of cannabis dependence (20.2 percent, against 11.9 percent for non-Māori). The risk of dependency is particularly high for Māori males.

This is why psychologist and film maker Paora Joseph says Māori appear to have a particular fondness for cannabis and the culture around it. Although it is not a traditional element of Māoritanga, the drug has been given something of a cultural status in some Māori communities.

“What I see is it’s kind of built into the culture,” Joseph says. “It’s been adopted as the norm.”

In his work and in the making of his acclaimed documentary Hiding Behind the Green Screen, Joseph has met many Māori who have adopted aspects of the Rastafarian culture associated with cannabis as their own – from music to dress to drug use.

“When it becomes habitual, a part of the culture, a part of daily life, that’s when it’s a problem.”

The habit is not only problematic for the health of the user but also the health of the user’s whānau. People talk past each other in a family where cannabis use is prevalent, Joseph says, and their interactions lack the depth necessary to adequately communicate.

Joseph says use of cannabis among Māori is increasingly intergenerational; he believes the drug becomes more embedded among Māori as each new generation is introduced to it. 

Cannabis and mental health

Hall says many researchers believed cannabis was a drug of dependence back in 1993, but they had no proof to offer those who said it was an easy drug to stop using. Since then, Hall says dependence has been proven, and this has been bolstered by evidence of large numbers of young adults presenting to treatment services requesting help to get off cannabis.

Today, researchers are largely agreed on the adverse effects of dependence. Young people using cannabis are more like to leave school early, fail to develop satisfying personal relationships and be dependent on welfare.

In 1993, researchers suspected a modest association between cannabis use and major depression. Boden says, in the intervening years, the Christchurch cohort has provided evidence of an association, although it is relatively weak and difficult to detect. There is a stronger association between cannabis use (in particular, cannabis dependence) and anxiety disorder.

Research has also established a link between cannabis and suicidal ideation, particularly in males. Boden says, by the age of 30, the vast majority of heavy users are male.

Hall says the link between cannabis and psychotic symptoms is strong, but the association with depression is harder to understand. Did users turn to cannabis because they were depressed, or did cannabis use drive their depression? 


Nadia Solowij is an Associate Professor at the University of Wollongong. For more than 20 years, she has focused her research on cannabis use. Her team works with key laboratories across the globe on projects utilising the latest neuro-imaging technology.

In 1993, as Solowij was just completing her PhD, she also presented at the Drug Foundation symposium. She discussed novel evidence showing the long-term effects of cannabis on cognition.

Cognition concerns brain function. Cannabis use seems to have the most impact on memory. Other aspects of cognition that are often impaired by cannabis use tend to be higher-functioning skills such as information processing, planning and executive abilities.

Impairment in these areas is most evident when the pressure is on, in cognitively demanding tasks. In 1993, this was not understood.

“Most people suspected there weren’t any long-term effects,” Solowij says.

It is still not certain whether cognitive recovery is possible after the damage has been done. Solowij suspects it is possible, but it could take a long time for the brain to normalise – particularly after long-term heavy use.

“The longer you use, and the more heavily, the more likely you are to be impaired.”

Solowij says the majority of the effects on cognition are relatively subtle. The effects may combine to make a person function less well, but they will still function in the community.

“So maybe, in the scheme of things, it is not so bad, but they do not function as well as they would if they hadn’t used cannabis.”

Solowij says IQ is another area impacted by cannabis use. Studies have shown that, over time, cannabis use will reduce a person’s IQ.

The most definitive study was a Dunedin cohort assessed during adolescence and again at age 38. Those who persisted with cannabis were shown to have lost eight IQ points over those 20-odd years.

In recent years, Solowij’s focus has turned to the complex area of schizophrenia and the key question: why do some people develop psychosis when they use cannabis and others don’t?

Predisposition to schizophrenia can’t be explained by a single gene. There are a range of individual differences, including genetic make-up.

Within the general population, about 1 percent of people develop psychosis. Researchers now know that, of these, 13 percent would not have developed psychosis if cannabis hadn’t triggered their vulnerability to the condition.

Back in 1989, a groundbreaking study revealed a link between cannabis and schizophrenia.

“Most of us didn’t believe it,” Solowij says.

Scientists stood alongside the general population in a belief that cannabis was “not that harmful”.

She says, “It took quite a long time before new studies started to emerge – a wide range of studies, large studies … It is fairly widely acknowledged now that there is a link [to schizophrenia]. It’s almost, I would say, undeniable.”

Like Hall, Solowij says recognition of the harmful effects of cannabis is a major change in the 20 years since 1993. It’s no longer considered the “healthy option” in terms of drug use.

“I don’t associate cannabis use as being particularly healthy at all. We know that there are a lot of harms associated with cannabis.

“I do think most people would recognise and acknowledge that it is harmful.” 

Cannabis and the human body

There is emerging evidence cannabis has a harmful effect on cardiovascular function. Regular users may also suffer from poor respiratory function and a higher risk of chronic bronchitis.

However, Hall says the cancer link you might expect to see with a product that is predominantly smoked hasn’t yet been conclusively proven or adequately quantified. The research is muddied because most people who smoke cannabis also smoke tobacco. Hall insists, due to the difficulties involved in isolating cannabis’s impact, the absence of evidence does not equate to exoneration.

But cannabis also offers health benefits.

Solowij says there is some evidence that cannabis use lowers intra-ocular pressure in glaucoma sufferers. Of all the medicinal claims associated with cannabis, this one is perhaps the most substantiated.

However, because the drug’s impact is short-lived, the positive impacts would subside after about three hours.

There is some research suggesting cannabis retards the growth of some forms of cancer. Studies showed breast cancer cells in Petri dishes stopped in their tracks when faced with cannabis, while a Spanish study found the chemicals in cannabis promoted the death of brain cancer cells.

(However, other research revealed testicular cancer was 70 percent more likely to develop in men who use cannabis.)

One of the major developments in cannabis research in recent years has been the identification of potential health benefits associated with cannabidiol (CBD).

Tetrahydrocannabinol (THC) is the compound responsible for the most infamous impacts of cannabis use – the stoned feeling, memory loss and, in an unfortunate minority, psychotic episodes.

CBD is another compound of cannabis. Over the decades, breeders have sought to increase the THC in their product, and Solowij says the CBD content has subsequently diminished or even been eliminated. This is of particular interest to researchers because early studies have shown CBD may have anti-psychotic and anti-anxiety properties. It’s believed CBD could provide neuro-protective and anti-inflammatory benefits in multiple sclerosis sufferers, control chemotherapyinduced nausea, prevent the formation of deposits in the brain associated with Alzheimer’s disease and help reduce HIV-related neuropathic pain. It is early days in terms of definitive results, but Solowij says CBD is now a major area of research for teams like hers.

Other new avenues for research

Canadian researcher Amy Porath-Waller regularly reviews Police reports. She says it’s now common for people to be using multiple drugs at once.

Porath-Waller says, 20 to 30 years ago, the levels of THC present in cannabis were much lower. Police hauls tested in Canada in 1985 showed 3.5 percent THC – in 2008, the average had risen to 12.5 percent. In the United States, THC levels averaged 9.8 percent in 2009, while in Australia, they were around 15 percent.

This increasing potency, combined with what is now known about the impact cannabis can have on the developing adolescent brain, provides an alarming backdrop to prevention efforts.

Steve Allsop, Director of Australia’s National Drug Research Institute, says 2013 is a fascinating moment in time for those interested in the criminal status of cannabis and the impact that status may have on the health of a population.

He values the opportunity to watch and learn from the experiences of Colorado and Washington, as they legalise cannabis use, production and sale, and other jurisdictions around the world that are decriminalising cannabis possession and use.

“A number of countries are making some substantial changes,” Allsop says. “There is an opportunity to watch and learn from that experience.”

Boden, who is American, is also intrigued by the changes under way as Colorado and Washington transition to a fully legalised cannabis trade.

“This could be the beginning of the end for prohibition in the States.”

With the legalisation of cannabis, he expects research into the impacts of the drug will expand and develop greater sophistication, and the next 20 years will reveal even greater knowledge of the impacts of cannabis use on human health. 

Sean Plunket: not a poster boy, just another New Zealander

Sean Plunket last smoked cannabis with doctors and surgeons at a New Year’s Eve party near Auckland.

The RadioLIVE presenter sees nothing extraordinary in that fact – or in the fact he’s talking about it.

Earlier this year, during a talkback segment on cannabis law reform, Plunket outed himself as an occasional cannabis smoker.

Health Ministry figures from 2010 suggest 14.6 percent of adults used the drug in the past year, and the Christchurch Health and Development Study reveals 75 percent of people have tried the drug by the time they are 25. While discussing cannabis, Plunket revealed he was among those who had used the drug in the past year.

The revelation was met with little response from the mainstream media, his audience or his bosses. “I didn’t consult anyone, and I don’t think it was regarded as a big deal.”

But he wouldn’t have been so complacent in 1993.He says, back then, he probably wouldn’t have had the confidence to speak openly about his drug use.

“It’s become less of an issue over the last 20 years.”

Plunket first tried cannabis in Standard 2, aged about eight, at parties he went to with his mother. This demystified the drug for him, and although starting young, he has never been a regular cannabis user.

“It was never a big deal.”

He purchased what he thought was cannabis at age 17 and was caught and suspended from boarding school. In retrospect, he believes he actually purchased herbal tea.

These days, there’s no chance he’ll be duped into buying a tinny of tea. Plunket doesn’t buy cannabis and doesn’t keep any in his house. He draws the line at purchasing cannabis because he doesn’t want his discretionary dollar going into the pockets of criminal enterprise.

But when he’s offered some at a party, he sometimes says yes. He says he smokes cannabis about five or six times a year.

“I don’t buy illicit or illegal drugs. If I’m offered marijuana in a social setting and I feel comfortable ... about my privacy, and I think it would be a social lubricant, like having a drink, I’ll have some.”

His preference for cannabis control would be a system where the drug is treated similarly to home-brewed beer: you could grow a small amount for yourself and have some mates over, but you couldn’t legally sell your crop.

Plunket, 49, says he will not be mirroring his childhood and exposing his son to marijuana to demystify the drug.

“I do not advocate minors using any form of drugs [including] cannabis or alcohol.”

Rather, his strategy is to raise a child equipped to make sound judgements regarding his safety and informed decisions about risk. It’s a plan that clearly acknowledges marijuana’s prevalence in New Zealand society

Plunket says he has no intention to become a poster child for cannabis law reform; his motivation was simply about honesty. He felt he couldn’t host a thorough debate about cannabis on his show without admitting that he was among the half a million New Zealanders who use cannabis.

“I’m a very, very average New Zealander, actually. I wouldn’t die in a ditch for alcohol law reform, and I wouldn’t die in a ditch for drug law reform. But how on earth are we going to have an honest discussion if grown adults won’t [admit] the place it has in New Zealand life?

“I’m keen for us to say as a country that, let’s be honest, marijuana permeates much of society. It’s not an uncommon recreational drug.”

Harms: the known, the probable and the unclear

In 2009, Professors Wayne Hall and Louisa Degenhardt wrote a review for leading journal The Lancet titled ‘Adverse health effects of non-medical cannabis use’. Below are excerpts of their findings:

What is known or probable?

  • Acute adverse effects of cannabis use include anxiety and panic in naïve users and a probable increased risk of accidents if users drive while intoxicated.
  • Use during pregnancy could reduce birthweight but does not seem to cause birth defects.
  • Chronic cannabis use can produce a dependence syndrome in as many as one in 10 users.
  • Regular users have a higher risk of chronic bronchitis and impaired respiratory function and psychotic symptoms and disorders (most probably if they have a history of psychotic symptoms or a family history of these disorders).
  • The most probable adverse psychosocial effect in adolescents who become regular users is impaired educational attainment.
  • Regular cannabis use in adolescence might also adversely affect mental health in young adults, with the strongest evidence for an increased risk of psychotic symptoms and disorders.
  • The public health burden of cannabis use is probably modest compared with that of alcohol, tobacco and other illicit drugs.

What is unclear?

  • In the case of depressive disorders and suicide, the association with cannabis is uncertain.
  • For cognitive performance, the size and reversibility of the impairment remain unclear.
  • Whether cannabis contributes to behavioural disorders in the offspring of women who smoked cannabis during pregnancy is uncertain.
  • Adolescent regular cannabis users are more likely to use other illicit drugs, although the explanation for this association remains contested.

The ‘gateway’ drug

Canadian researcher Amy Porath-Waller has analysed various studies into the role of cannabis as a gateway drug. Does cannabis use lead to the use of synthetic drugs capable of causing more harm? The debate was raging 20 years ago, and there’s still no definitive answer.

Dr Porath-Waller, a senior research and policy analyst at the renowned Canadian Centre on Substance Abuse (CCSA), says, unfortunately, there is no definitive answer to this recurring question. The findings are mixed. There is quality research to prove it and equally sound and compelling research to disprove it.

However, researchers in her network say young people report that they do see cannabis as a gateway drug.

She and her colleagues hear that young people go to their drug dealer to pick up cannabis and are offered ecstasy.

“Just by using cannabis, they are getting exposed to other drugs.”





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