The impact of cannabis policy changes on cannabis use among adolescents: evidence from Europe

Background and aims: According to the most recent European Drug Report (EMCDDA, 2018), cannabis remains the most widely used illicit drug and accounts for the largest share of the illicit drug retail market in the European Union. To tackle this longstanding problem, over the last two decades a broad set of reforms to national cannabis control policies have been implemented, but their effectiveness in achieving the desired results is unclear.

In recent years increasing attention has been devoted to the effects that these reforms might have on the consumption behaviour of young people, particularly because of the high prevalence of use and because the onset of cannabis use typically occurs among adolescents who are particularly vulnerable to the development of related disorders. However, few empirical studies investigated the policy impact on adolescent cannabis use, and even less adopted an European perspective. To address this gap, the present work analyses the impact of selected categories of policy reforms on cannabis perceived availability and use among European adolescents over 17 years.

Methods: Using the categorisation proposed by EMCDDA, cannabis control policy reforms were classified into five main types based on the treatment of cannabis possession for personal use. Data about cannabis consumption and perceived availability among 309,235 students aged 16 from 20 European countries between 1999 and 2015 were drawn from the European school Survey Project on Alcohol and other Drugs.

Our identification strategy is based on a difference-in-difference model, which application is allowed by the fact that only thirteen out of twenty of the countries included in our analysis implemented relevant reforms in the period, leaving us with a control group of seven countries.

As regards the outcome measures, self-reported perceived availability was analysed among the whole population, frequent users (20 times of more in the last month) and non-frequent users. Cannabis use in the past year was analysed among all users, experimenters (one or two times), non-frequent users and frequent users.

Results: Concerning cannabis availability, none of the more liberal reforms displayed an effect, and only some of the more restrictive had an impact on the availability perceived by the whole adolescent population. This effect persists only among non-frequent users, whilst no relevant effect is shown on the frequent ones.

With respect to the use of cannabis, only some drug policy reforms had an impact, and this impact was different for experimental and non-frequent users. However, as for the perceived availability no reforms had an effect on frequent users.

Conclusions: The results suggest that selected categories of reforms do affect the availability and prevalence of cannabis among adolescents. In particular, some forms of restrictive intervention reduce the extent of its use. Consistently, more liberal reforms seem to cause an increase in the share of students approaching cannabis. However, no policy reforms, notwithstanding their nature, seem to be able to reduce the proportion of those adolescents that making a frequent use among all are more at risk of experiencing use-related harms, nor their perception of the availability of the substance.