Q&A: New Zealand Voters, Soon To Decide on Adult Use, Have Science in Their Corner


With the recent rollout of a medical cannabis program in April, cannabis operators in New Zealand have barely gotten up and running. But this week, on October 17, voters will get to say Yes or No to a measure with more sweeping implications—one that would allow people twenty and over to buy up to fourteen grams of cannabis a day at licensed outlets, grow up to four plants per household, and consume cannabis privately and at licensed locations. The referendum is not “binding,” meaning, a “Yes” vote would not immediately trigger a legislative change unless the government agrees to enact the results.

For New Zealanders on the fence, there are a number of considerations: the health impacts of cannabis, the social consequences, and the impact of past prohibition. And fortunately, a group of New Zealand researchers, armed with a pair of long-term studies, are here to help. 

An overview of the studies, published in the Journal of the Royal Society of New Zealand, evaluates the two long-term studies, which followed thousands of participants in New Zealand born in the 1970s. The Christchurch and Dunedin studies, as they’re informally known, collected information about participants’ lives, including their cannabis use, at various ages. Because the studies sampled a large, diverse swath of the population and monitored participants over decades, the overview provides a rare look into New Zealand’s relationship with cannabis. 

Some results: Almost 80% of study participants had tried cannabis, and most did so without serious consequences. A small portion (five to ten percent of the population)—because they started using cannabis as adolescents and continued into adulthood, used cannabis frequently (more days than not), or had become dependent on it—were at a higher risk than the rest of the population for negative effects. These effects include psychological impairment, respiratory problems, lowered cognitive capacity, lower educational achievement, and risk of incarceration. 

Yet the criminalization of adult-use cannabis does not make people more safe, the authors conclude. “The illegal status of marijuana does not prevent some people from using, and arrests and convictions do not lead to a reduction in use,” they write. “Further, criminalising drug use can deter individuals from seeking or getting appropriate help.” But they do urge the government, if voters choose legalization, to prioritize measures to keep cannabis out of the hands of adolescents, who the studies show were the most affected by continual use. 

Cannabis Wire spoke with Kirsten Robertson, a University of Otago researcher who contributed to the review. We spoke about the studies themselves, the conclusions one can draw, and what’s on the horizon for New Zealand and cannabis. (This Q&A has been lightly edited for clarity.)

Sophie Putka, Cannabis Wire: How did you come to study this area?

Kirsten Robertson, University of Otago: Credit for the study has to go to the two directors, professor Richie Poulton and Joseph Boden, because I’ve only really come on to this team recently. So how did I get into this area? My background is psychology and I ended up in marketing. But I’ve always done research looking at psychosocial factors. I’ve done quite a lot of research on student alcohol consumption, and recently I’ve also been doing research in cannabis and students’ use of cannabis and what controls how regularly they use. 

Cannabis Wire: Did the idea for the study arise out of the upcoming referendum, or had it already been in the works? 

Kirsten Robertson: This particular paper was born out of the fact that the referendum was coming up. There’s been lots of research on the area, but this one was directed at informing the voting public. Part of the reason was, basically, we feel that debate should be informed by robust research. Obviously, as you know, cannabis legalization is a hotly contested topic. There are really polarized views. And we just wanted to make sure that we could provide a view based on reliable and robust evidence. It was because we had all this world class information on the natural history of cannabis, and its use and its consequences, and we wanted to bring that all together to inform the voting public. 

Cannabis Wire: Is that common? Of course, people reference studies when they’re creating legislation, but as far as a study that’s specifically geared toward the public to inform them…?

Kirsten Robertson: I suppose it’s aligned with the move more towards, “research should have real world implications.” And I guess a lot of research wouldn’t be so bold to be able to say that’s what they were doing, but because these are world renowned studies, and they are so robust, you can have confidence. 

Cannabis Wire: What were some of the things that surprised you or the rest of the team in what you found?

Kirsten Robertson: One of the main points that came through is that cannabis use is quite normative and commonplace in New Zealand. So despite it being illegal, the majority of New Zealanders, or approximately 80% born in the 1970s, had used cannabis at least once by the time they were approximately thirty. Despite it being illegal, it’s really common. Probably roughly half the population in the studies had used in any one year during their twenties. One of the main findings, and this isn’t unique to the study, is that the law is not working. It’s ineffective. Ninety-five percent of those arrested or convicted either continued using at a similar rate or even increased the rate post-arrest. So the law is not stopping people from using cannabis. 

But unfortunately, those people that are arrested or convicted for using cannabis, which we now know is a normative behavior, it has a significant impact on their life. It can affect their employability, their freedom to move globally, and it leads to ongoing discrimination and stigma. Another problem we have in New Zealand is that cannabis law has been found to be enforced inequitably, so there is a racial bias towards arresting and convicting Māori compared to non-Māori. So in terms of the current law, it is not working. And one of the other things that surprised us was that the majority of cannabis users did so with little or no harm. So it was only—it was approximately five to ten percent of the overall population who were at heightened risk. And these risks were pretty much confined to those who began using an early- to mid-adolescence, or were using frequently.

Cannabis Wire: In terms of the landscape of what New Zealanders do and don’t know about the effects of cannabis, has there been much public health education that would inform people about cannabis? What is the level of knowledge? 

Kirsten Robertson: Unfortunately, because cannabis is illegal, that actually muddies the water and prevents those kinds of education programs happening in schools. So that’s one of the reasons why people need to consider carefully what’s best going to lead to a harm minimization focus. It’s really difficult to teach people about something that is illegal.

Cannabis Wire: How will you reach folks with this study? 

Kirsten Robertson: Richie Poulton has been played on two of our main television channels, and he’s also done an interview on one of our main radio stations. So I believe that information is already reaching the voting public, which is great. 

Cannabis Wire: Outside the referendum itself, what kinds of policy implications does this information provide for the future?

Kirsten Robertson: Regardless of the outcome of the referendum, the most important policy beyond legalization is protecting adolescents. So we really need early intervention approaches. We need to concentrate on delaying the onset of cannabis use until adulthood. And to help this happen, we need education programs targeting adolescents.

Cannabis Wire: What would those look like? 

Kirsten Robertson: We haven’t gone into that in the paper, so anything that I say is more my opinion than based on the research. But if you consider the fact that at the moment, adolescents are told that cannabis is illegal, so to them, it’s like the fun police telling them ‘just don’t do something.’

But if you’re actually telling adolescents, ‘If you put off using cannabis until you’re eighteen, you’re going to reduce your chances of having all of the risks of negative outcomes such as impairments in your psychological functioning, the loss of cognitive capacity, negative psychosocial outcomes.’ If you actually told them the honest and non-judgmental truth about the consequences they could suffer and how they can minimize that risk, it’s essentially just giving them the facts based on evidence. It’s got to be a lot more compelling to an adolescent than just be told ‘you can’t do that. It’s illegal.’

Cannabis Wire: This isn’t necessarily related to the research itself, but is there a general sense of what people are leaning toward, in terms of the referendum? 

Kirsten Robertson: So unfortunately, there are polls and they are just fluctuating. So it is definitely too hard to call. One poll will come out with people more in favor and another poll comes out and they’re not quite—it’s very close. 

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