In 2018, Canada became the second country to legalise cannabis. This was the topic of a recent Addiction Audio podcast with Dr Janni Leung. The SSA’s Natalie Davies unpacks some of the key findings from Janni’s work and considers what it means to judge the effectiveness of a policy or intervention from a public health perspective.

It is five years since cannabis was legalised in Canada, and its impacts are debated. It is a complex and evolving issue with significant local, legal, and health implications.

Dr Janni Leung is a National Health and Medical Research Council Emerging Leadership Fellow at the National Centre for Youth Substance Use Research, The University of Queensland. Dr Elle Wadsworth interviewed Janni on episode seven, season two, of Addiction Audio about her research into the implementation and public health impact of cannabis legalisation in Canada.

In 2001, it became legal in Canada to use cannabis for medical reasons. Then, in 2018, the Cannabis Act was introduced, and it became legal to produce and sell cannabis for non-medical reasons to adults. The aim of the legislation was to: protect the health of young people by restricting their access to cannabis; minimise incentives to use cannabis; allow the legal production of cannabis to replace the illicit cannabis market; deter illicit cannabis production and sale by appropriate sanctions and enforcement; reduce the burden that dealing with cannabis offences imposed on the criminal justice system; enable cannabis users to have a quality-controlled supply of cannabis; and increase public awareness of the health risks of using cannabis.

Janni and colleagues examined the public health impact of this legislation. They conducted a systematic literature review and published a narrative summary of their findings in the journal Addiction.

Broadly speaking, public health is “the science and art of preventing disease, prolonging life and promoting health and wellbeing, through the organised efforts of society”. In their study, Janni and co. reported on a wide variety of public health-related outcomes, including:

  • cannabis-related arrests
  • potency of cannabis products
  • legal cannabis prices
  • cannabis-related car crashes
  • cannabis-related visits to the emergency department

Two of the headline findings were: (1) evidence of a substantial reduction in cannabis-related arrests; and (2) evidence of a substantial decrease in the price of legal cannabis.

Police data on cannabis-related arrests between 1987 and 2019 reportedly showed a sharp decline in the number of people arrested for cannabis possession and cannabis use after legalisation. These results are promising for public health. A reduction in cannabis arrests means “less police time and resources have been spent on arresting people for cannabis use, and the individuals were no longer being criminalised for possessing and using cannabis”.

After legislation, there was also evidence of a marked decrease in the price of cannabis products, which meant that “Canadians have been able to buy more cannabis products at lower prices after legalisation”, including “a larger selection of different products such as edibles and drinks, various concentrated products”. Although this would make cannabis more accessible, it would also arguably promote safer consumption practices because people would be using products that are monitored and regulated. Again, this would be promising for public health.

Janni notes that, overall, there is evidence that the legislation is achieving what it intended to, for example, reducing the burden on the criminal justice system and allowing legal cannabis to replace the illicit cannabis market. However, she also says that the impact of cannabis legalisation is a “complex and evolving issue”. Elle asks her more about this, including the limitations of a systematic review.

“Because this is a systematic review, that means we have relied on data that have been already been published…and there’s often a lag between what’s happened in the population when the data were collected, and then when the data have been written up, peer-reviewed, and published.”

Janni says that any systematic review is limited by the available data. In this case, most of the data went up to 2020, which was only two years after legalisation, and therefore, doesn’t leave a big window of time to assess the impact of the legislation. Elle adds to this that the market has changed quite a lot in a short period of time. For example, in 2018, only dried flowers and some cannabis oils were available, and then in 2020, other non-flower products entered the market. Janni talks about what it means to conduct a systematic review in this type of context, agreeing with Elle’s words that “a systematic review of the impact of legalisation is something the academic world should frequently repeat as the markets age”.

“I agree that the monitoring and review should be ongoing and repeated, so that more updated information can be made available to everyone.”

It is now five years since cannabis was legalised in Canada, and Janni hopes that this review will be a resource that policymakers, researchers, and the public can refer to “to make informed decisions based on a comprehensive understanding of all the research evidence”.

Listen to the full episode of the Addiction Audio podcast to hear more from Dr Thomas Brothers, including about cannabis marketing and packaging, and the impact of more widely-accessible edible cannabis products on young people.

Original article: The implementation and public health impacts of cannabis legalization in Canada: a systematic review. By Wayne Hall and colleagues. Published in Addiction (2023).

by Natalie Davies

Editor’s note: Quotes have been condensed and edited for clarity.

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