Health – Legalising cannabis in NZ: what does the evidence say?

Legalising cannabis could have important positive implications for social equity outcomes, particularly for Māori.

The Office of the Prime Minister’s Chief Science (PMCSA) has released an accessible evidence summary, titled ‘Legalising cannabis: What does the evidence say?’ (

Produced by a multidisciplinary expert panel, the internationally peer-reviewed summary is designed to support informed decision making in the upcoming cannabis referendum.

The panel was convened by the PMCSA, Professor Juliet Gerrard, and co-chaired by Professor Tracey McIntosh (Tūhoe), the Chief Science Advisor to the Ministry of Social Development.

The expert panel’s work arose from a request in 2019 from the Prime Minister.

The website does not tell readers how to vote, but rather guides them through the available evidence, with all its uncertainties and flaws.

Gerrard says that, “The key question isn’t whether cannabis does harm – we know it does for some users, but not for others. This is true whether we legalise it or not. Rather the vote asks us to decide whether a legal regulated framework will increase or reduce cannabis-related harm.”

We recognise that the topic is complex and multifaceted, so it is important that people have trusted and accessible information on which to base their decision, McIntosh says. “We have drawn on evidence from here and overseas to consider the wide-ranging impacts of changing this law – from how it might impact health-related harms, to how it could change social and community outcomes.”

The overseas experiences in Uruguay, Canada and some states in the US give us clues about the possible impacts of legalisation in Aotearoa New Zealand, but the evidence is uncertain, reflecting the short time since changes were made and the different regulatory approaches.

“The evidence is mixed and constantly evolving. As an example, the impact of legalisation on rates of cannabis use among young people is unclear. Some studies show no change, others show a small increase and others a small decrease. What we haven’t seen is evidence of any dramatic changes in cannabis use by young people. It’s important to remember that our local experience would depend on our unique environment and approach,” Gerrard says.

What we do know is that the current law causes harm to sectors of our community, McIntosh says. “The evidence shows that Māori are more likely to be arrested for and convicted of cannabis-related offences than non-Māori, even after adjusting for rates of use. The social harms from contact with the criminal justice system, especially from having a drug conviction, are lifelong and impact the wider whānau too. Legalising cannabis could have important positive implications for social equity outcomes, particularly for Māori, and could broaden and empower community responses to prevent social harm.”

Making an evidence-based decision is not clear-cut, Gerrard says, but the experience overseas provides a useful guide. “It comes down to personal judgement. Is the proposed regulatory framework likely to reduce harm, or not? And how much weight do you give to the social harm that is caused by the current illegal status of cannabis?” The panel hopes this body of work helps people to consider the wide-ranging impacts of legalising cannabis and to make an informed decision in the referendum.

What’s covered in the evidence summary?

  • an explanation of current laws and why Aotearoa is considering legalisation
  • an at a glance summary of what might happen if we vote ‘yes’ or ‘no’ to legalising cannabis
  • detailed FAQs that address a range of issues related to cannabis legalisation
  • overseas case studies of cannabis law reform
  • further reading for a deeper dive into certain issues
  • links to key cannabis articles in the news
  • more detail about our panel members

Independent documentary on cannabis legalisation evidence

Alongside the website, documentary filmmaker Shirley Horrocks is releasing a short film summary of some issues surrounding cannabis legalisation and the referendum. This is the second film in her independent series covering the role of science advice to government. The film includes commentary from some researchers and clinicians who were part of the Chief Science Advisor expert panel, as well as other experts. It is independent of the work of the panel but supports the efforts to communicate the evidence to the public to help inform people ahead of the referendum. The documentary is available at

Prime Minister’s Chief Science Advisor

Professor Juliet Gerrard is the Prime Minister’s Chief Science Advisor, Kaitohutohu Mātanga Pūtaiao Matua ki te Pirimia. This is a wide-ranging role centred around advising the Prime Minister on how science in its very broadest sense can inform good decision making in Aotearoa New Zealand. Gerrard has a vision for the role around four principles: rigorous, inclusive, transparent and accessible. She aims to create a trusted bridge between science, society and government.

Chief Science Advisor to the Ministry of Social Development

Professor Tracey McIntosh is the Chief Science Advisor to the Ministry of Social Development. This role, like other CSA roles, aims to enhance evidence-based policy development and to provide sustainable, inclusive and equitable outcomes for Aotearoa New Zealand.