Cannabis concerns: What experts say as referendum on legalisation looms

As the question whether or not to legalise cannabis for people aged 20 and over is set to be voted on by the public, the implications of a New Zealand with a legalisaed cannabis model are not yet known.

File picture. Source:

However, concerns around possible impacts have been widespread. We ask experts that have studied legalisation to share their findings: 

Will legalising cannabis increase the use of hard drugs and crime?

Economics senior lecturer Yu-Wei Luke Chu studied the impact of medical cannabis and recreational cannabis legalisation in the US - with decreases found in some areas of hard drug use and no increase in violent and property crime.

Drug use (file picture). Source:

"The empirical evidence from the US on medical marijuana and recreational marijuana finds that marijuana use, especially heavy marijuana use had increased.

"There is direct social cost associated with the increase in marijuana use, for example, more people go to rehab facility due to marijuana addiction. However, there isn't much negative impact on other social outcomes. In fact, most research find positive outcomes.

"There appear to be decreases in heroin and opioid usage, no change in cocaine use, decreases in drunk driving, suicide, obesity, no increase (perhaps small decrease) in violent and property crime, no change in labour market participation. There isn't much research finding negative effects from these laws, although I have a paper actually finding negative effects on university students study time (they study less and watch more TV)."

Yu-Wei Luke Chu expected legalisation in New Zealand would have similar impacts.

"We will see increases in cannabis consumptions but probably not strong negative impacts on other social outcomes like crime or hard drug use. I won't rule out small increases in petty crimes like break-ins as the industry is largely a cash business."

I’ve heard cannabis is bad for your health, especially for people under 25. What are the health implications and how could legalisation effect that?

Otago University’s Department of Psychological Medicine Associate Professor Joe Boden says the three major areas that can be impacted by frequent cannabis use (once a week or more) by people under the age of 25 (under a prohibition model) are:

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Social psychologist Dr Joe Boden say those people can’t seek help because of current laws making cannabis illegal. Source: Breakfast

1. Amotivational syndrome – "The younger you are and the more you use cannabis, the less likely you are to complete education programmes, NCEA, or to enrol in university. You are less likely to complete a degree compared to people who use cannabis later in life or not at all, and the more likely you are to experience long periods of unemployment under 25 or to be reliant on welfare."

Professor Boden said the higher use of cannabis by people under 25 sees people more likely to get trapped "into this amotivational cycle where your life is passing you by".

2. Gateway effect – the use of cannabis increases the likelihood more illicit drugs may be used.

"The younger you start, and the more heavily you are using the greater your risk of using more illicit drugs. However, in the Netherlands (there it is decriminalised), it was found there was not a gateway effect from cannabis, which could be due to not being in contact with drug dealers. The idea would be if you were to legalise recreational cannabis this gateway effect would likely disappear."

3. The link between cannabis use and the experience of psychotic symptoms when not directly under the influence of the drugs – Particularly at younger ages you are much more likely to experience psychotic symptoms (which is still quite rare). There is an 80 per cent increase for those under 25, compared to those who did not use cannabis.

I asked what he thought of the proposal to limit cannabis purchases to those aged 20 and over.

"It’s a good compromise... sensible regulation with cannabis reduces consumption and harm."

What about incarceration rates and what will happen to the black market?

Dr Marta Rychert of Massey University's College of Health told the Science Media Centre more than 2000 people in New Zealand are convicted of cannabis use or possession annually, but from 2016/17 "cannabis possession was the only offence in just 400 cases, and only three of these resulted in imprisonment".


"This would suggest that incarceration rates will not change dramatically... but the length of incarceration and life impacts from conviction will be reduced.

"This is significant, as a cannabis conviction can have life-long implications for employment, travel opportunities and living arrangements, and these disproportionately affect Māori."

"Early evidence from Colorado shows black market activity is likely to persist, at least in the early stages of legalisation. A legal, regulated cannabis market can offer a number of advantages over the black market, including quality, consistency and safety of products. The impact of legalisation on the black market will depend on how well these aspects are controlled and how well they respond to cannabis user expectations," Dr Rychert told Science Media.

How are high doses in edible cannabis controlled? Will there be cannabis-infused gummy bears?

CEO of the National Institute for Cannabis Health and Education in Canada, Jenna Valleriani, said it was a balancing act "of trying to compete with the unregulated market and ensuring these products are packaged properly and have appropriate limits".

"For example, setting a standard dose so consumers know what one serving looks like, as well as restricting maximum THC in one package. Colorado and Canada uses a 10mg maximum."

"This is fairly low compared to what's available on the unregulated market (up to 400mg of THC in one package)."

Associate Professor Joe Boden said there needed to be strict labelling requirements of THC, as well as charging by the amount of THC in the product which he said discourages the consumption of high THC products.

He also said requirements such as that in Colorado prohibited any configuring or shaping of the products as lollies to be marketed to children. Colorado's regulation came after edibles were accidentally ingested by children. 

What happens with driving rules? How will drivers on cannabis be tested? Will cannabis use impair driving?

Dr Rychert also told Science Media, "cannabis intoxication affects driving abilities, it has been estimated to increase crash risk approximately two times".

"Drug driving is a challenging policy issue and many countries that have legalised cannabis implemented policies to ensure safety on roads. These include tests of behavioural impairment, saliva and blood testing. Unlike alcohol, cannabis impairment is much harder to detect by standardised methods. It seems that some combination of behavioural impairment and laboratory testing can be a feasible way forward to detect cannabis-impaired drivers.

"Just like with alcohol, a strong education campaign and enforcement is needed."

Will legalisation stop people from using synthetics?

Head of the Otago's Department of Pharmacology and Toxicology Professor Michelle Glass told the Science Media Centre that in the international market this has not been the case.

Source: 1 NEWS

"People are continuing to use synthetics despite the clear evidence of harm from them. There seem to be two main reasons for this, one, they aren't detected in most work place drug testing; and two, they are generally cheaper than cannabis."