A leading researcher says the health impacts of cannabis on young people needs to be taken into account before any law change.

Associate Professor Joe Boden was responding to the news this week that the Government may push ahead with a public referendum on legalising cannabis for personal use before the 2020 general election to make sure it did not overshadow the election campaign.

Labour agreed to hold a referendum “at or before” the 2020 general election as part of its confidence and supply agreement with the Greens.

Boden, a researcher with the University of Otago’s longitudinal Christchurch Health and Development Study (CHDS) said any move to free up the drug’s availability needed to take account of scientifically-robust data showing regular use in young people was associated with a higher risk of mental health issues, use of other substances, and lower levels of achievement.  He recently outlined his study’s more than 20 years of data on cannabis use and its effects at a public talk.

He said CHDS findings shows more than 80 percent of middle-aged Kiwis have used cannabis at least once with little long-tern harm. But it also crucially found that in young, regular users, the drug could later effect their mental health, use of other illegal drugs and earning potential; which suggested any law change should restrict access to protect this vulnerable group.

The CDHS is a world-renowned longitudinal study whose researchers have followed more than 1000 Cantabrians born in Christchurch in 1977, including their substance use.

Boden crunched the numbers relating to cannabis use and harm for the public talk, and found:

  • More than 80 per cent of CHDS participants, now aged in their early 40s, had used cannabis at least once in their lives.
  • For the majority of people, casual or infrequent use of the drug is not associated with long-term negative outcomes.
  • Those who used the drug at least weekly during their teenage years were almost twice as likely as others to experience symptoms of psychosis than infrequent or non-users.
  • Those who used the drug at least weekly up to age 25 were over 10 times more likely to use other illegal drugs.
  • Less than 20% of those who started using cannabis before age 15 achieved a tertiary qualification, compared with nearly 30% among those who did not use cannabis before 18.
  • By age 25, those who used cannabis at least weekly as a teenager were three times more likely to experience long-term unemployment than those who did not use cannabis, or who used cannabis very infrequently.

Boden said the public should be aware of scientific evidence around cannabis before the proposed referendum on legalising cannabis.

“The CHDS data, along with data from other New Zealand and international studies, suggests that the harms of cannabis are most pronounced for those who begin using at younger ages, or who use cannabis heavily during adolescence. Any change to the law concerning cannabis needs to be undertaken in a way to reduce harm in this group, and in particular to provide resources for the treatment of those who develop cannabis dependence”

Boden said the evidence from his research group over more than 20 years suggested it was important any law change protects the most vulnerable and is not just a change to the ‘open slather free market’ model alcohol currently enjoys, with the many known associated harms. The impact of any law changes needs to be carefully studied, he said.

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  1. Sorry association is not causation

    When the UK downgraded cannabis from B to Class C for three years use among young people dropped!

    Holland decriminalised cannabis more than two decades ago and use among young people is lower than most countries who fiercely prohibit the drug

    Poortugal decriminalised all drugs almost two decades ago and have much lower rates of addiction than other countries, fewer fatal overdoses and lower HIV infection rates.

    I think you’d be better talking about the very real harms to young peoples lives and future by drug prohibition and criminalisation

  2. The harms caused by drug prohibition to young people who may use banned drugs:

    Additional risks arise when drug possession is made illegal, the user:

    1. Has no idea of the strength of the drug – it could be so strong it could result in risk of overdose or death.

    2. Has no guarantee about the purity or indeed content of the drug – it could be contaminated or even mixed with toxic ingredients that could cause serious harm, even death.

    3. Has to buy the drug ‘underground’ – exposing the person to the vagaries of a potentially dangerous criminal underworld.

    4. Buying, using and sharing illegal drugs puts the person at risk of serious criminal sanctions such as a community sentence with a drug rehabilitation requirement or even imprisonment.

    5. A person using an illegal drug risks acquiring a criminal record for a drugs offence – which could have lifelong consequences upon employment prospects, opportunities for world travel and housing.

    6. Has to use the drug in secret. For some people this may mean using in an isolated location which could be potentially dangerous especially when intoxicated – such as a condemned building, under a railway bridge, by a river or canal etc.

    7. Has to hide the use of illegal drugs making it more difficult to manage and harder to seek help, support or advice if a problem arises.’

    Buchanan J (2009) Understanding and misunderstanding problem drug use: working together, in R Carnwell & J Buchanan (eds) Effective Practice in Health, Social Care & Criminal Justice: A partnership approach, Open University Press, Maidenhead.


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