Legalisation of adult-use cannabis not linked to rise in problematic use – study

The legalisation of adult-use cannabis in Canada has not led to an increase in problematic use, according to a new study.

Researchers at the University of Waterloo have explored the potential changes in problematic cannabis use, following the legalisation of adult-use cannabis in Canada in 2018.

As part of the study, they assessed rates of ‘high risk’ cannabis use among people aged 16 to 65 in the years immediately prior to and following the legislation change. They also examined differences in problematic use by socio-demographic and socio-economic factors and changes over time.

Their findings, which are published in the journal Drug and Alcohol Review, show that in the two years following legalisation, there was ‘no evidence of a change in the proportion of those whose cannabis use would be classified as ‘high risk’’.

They also identified that problematic use differed by socio-demographic factors. According to the paper, cannabis consumers who lived in more deprived neighbourhoods were more likely to experience ‘moderate’ vs ‘low risk’ compared to those living outside deprived neighbourhoods.

The researchers concluded: “The risk of problematic cannabis use does not appear to have increased in the two years following cannabis legalisation in Canada. Disparities in problematic use persisted, with some racial minority and marginalised groups experiencing higher risk.”

Evidence that legalisation can be implemented ‘without compromising public safety’

Previous studies from Canada and the US, have also failed to identify any increase in problematic cannabis use following legalisation.

Research published in 2022 funded by the National Institutes of Drug Abuse (NIDA), explored whether US state legalisation of adult-use cannabis was associated with increased use among adolescents. The authors concluded that the change in legislation was ‘not significantly related to within-person change in the probability or frequency of self-reported past-year cannabis use’ among adolescents.

Other studies have found that legalisation of adult-use cannabis is not associated with an increase in other substance misuse, refuting the well-known ‘gateway drug’ theory. A paper published last year by researchers at the University of Washington, also found that young people consumed less alcohol, nicotine, and non-prescribed pain medication after legalisation. 

While the legalisation of cannabis may lead to an increase in consumption, this doesn’t necessarily mean a rise in problematic use. A study of more than 3,400 adult twins, from the  University of Minnesota and the University of Colorado, found a 24% increase in cannabis use in states where it had been legalised, but the increase in use was not accompanied by ‘increased problems’ or ‘adverse consequences’.

Commenting on the latest study, US NORML’s deputy director, Paul Armentano, said: “Canada’s real-world experience with marijuana legalisation, much like the experiences in many US states, affirms that these policies can be implemented in a way that provides regulated access for adults while simultaneously limiting youth access, discouraging misuse, and not compromising public safety.”

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