Study: Cannabis prohibition does not deter young people from using it

At a time when policy-makers are increasingly faced with the choice of reforming cannabis policies - and in particular abandoning the prohibitionist model for more liberal policies - research on the subject is essential. It enables policy choices to be based on evidence.

Nevertheless, this so-called evidence is often open to interpretation. In 2015, for example, a study often cited to justify continued prohibition suggested that liberalizing cannabis policies was associated with a significant increase in teenage use. A recent re-analysis of these results shows that a simple change of method leads to different results.

Further analysis

Researchers at the University of Kent wanted to test the validity and relevance of the study's findings. They used the same database, an HBSC survey of over 100,000 teenagers in 38 countries. Using a different method, their re-analysis revealed different results. Firstly, they took into account the entire survey, parts of which had been sacrificed by previous researchers. Secondly, they used a linear mixed-effects model in which they included lines for gender and country, as these are variables that can have an effect on the likelihood of juvenile consumption.

By adding these variables, expanding the database and opting for a more advanced statistical model, it was possible to find a different statistical relationship between cannabis policy liberalization and growth in the rate of youth use. The association between the two becomes statistically insignificant. The researchers conclude that the conclusions of the original study are not supported by a detailed and convincing interpretation of the numerical results.

Research and policy

“This is useful information for governments as they seek the best way to deal with cannabis. As things stand, the harms and costs associated with imposing criminal convictions on individuals using cannabis do not appear to be justified by any effect in terms of reducing consumption,» explains Professor Alex Stevens, who oversaw the study. What's more, these results are corroborated by other studies in states that have legalized cannabis.

For Ian Hamilton, Senior Lecturer in Mental Health and Addiction at the University of York, the illegality of cannabis is not a deterrent for young people - on the contrary: «For some people, the fact that it's illegal is part of the appeal, so if a country decides to open up access to regulated cannabis, this is likely to reduce some of the appeal». At the same time, regulated access means government-controlled access. In Canada, for example, cannabis can only be purchased with an identity card. Supplying cannabis to a minor is considered a crime punishable by up to 10 years' imprisonment.

In any case, this analysis shows that research findings are always open to interpretation. For example, other anti-cannabis arguments supported by the research may be qualified by factors that the researchers deliberately or unconsciously failed to take into account. Concerning cannabis and mental health for example, no causal link has yet to be discovered. These are simply statistical associations, which may be influenced by the fact that some users already have mental health problems, or find themselves in difficult life situations that influence both their mental health and their drug use.