This originally appeared at


, Silvia S. Martins d, Magdalena Cerdá baViolence Prevention Research Program, Department of Emergency Medicine, UC Davis School of Medicine, United StatesbDepartment of Population Health, Division of Epidemiology, New York University School of Medicine, United StatescSociety and Health Research Center and School of Public Health, Universidad Mayor, ChiledDepartment of Epidemiology, Mailman School of Public Health, Columbia University, United StateseNational Drug Observatory of Uruguay, Executive Tower Building, 10th Floor, Plaza Independencia 710, Montevideo C11000, Uruguay

Available online 6 May 2020, Version of Record 6 May 2020.



In 2013, Uruguay became the first country in the world to legalize recreational cannabis, instituting a non-commercial state regulatory model of production and supply. This study provides the first empirical evidence on its impacts on adolescent use of cannabis and related risks.


We use a generalization of the synthetic control method (SCM) to estimate the impact of legalization in Uruguay on adolescent past year and month cannabis use, perceived availability of cannabis and perceived risk of cannabis use. We compare biennial high school student self-reported survey data from Montevideo and regions in the interior of Uruguay post-legalization (2014–2018) and post initial implementation (2015–2018) to a synthetic counterfactual constructed using a weighted combination of 15 control regions in Chile.


We find no evidence of an impact on cannabis use or the perceived risk of use. We find an increase in student perception of cannabis availability (58% observed vs. 51% synthetic control) following legalization.


Our findings provide some support for the thesis that Uruguay’s state regulatory approach to cannabis supply may minimize the impact of legalization on adolescent cannabis use. At the same time, our study period represents a period of transition: pharmacy access, by far the most popular means of access, was not available until the summer of 2017. Additional study will be important to assess the longer-term impacts of the fully implemented legalization regime on substance use outcomes.


In December 2013, Uruguay became the first country in the world to legalize the sale, cultivation, and distribution of recreational cannabis, putting it at the forefront of a growing list of nations and states in the U.S. that have liberalized their cannabis laws in recent years. Unlike the for-profit commercial models that have been adopted in a number of U.S. states such as Colorado, Washington, and California, Uruguay’s approach to legalization is a non-commercial regulatory one. In Uruguay, the government controls all large-scale production, requires registration and limits the weekly quantities that a user may purchase, and prohibits advertising in all its forms (Cerdá & Kilmer, 2017). Given the unprecedented changes in cannabis policy that are taking place across the globe, and the growing number of jurisdictions considering some form of legalization, it is critical that we understand the impacts of different legalization models on drug use and related health and social outcomes.

The present study provides the first empirical evidence on the impact of legalization in Uruguay, examining adolescent cannabis use. The effect of cannabis legalization on adolescent use is of particular importance given evidence that heavy and chronic cannabis use in adolescents is associated with an elevated risk of developing cannabis use disorder (Stinson, Ruan, Pickering & Grant, 2006), cognitive impairment, and neurodevelopmental complications (Batalla et al., 2013; Meruelo, Castro, Cota & Tapert, 2017). Although those under the age of 18 are not legally permitted to purchase or consume cannabis in Uruguay, nor, for that matter, in any other jurisdiction that has legalized, there are a number of mechanisms by which legalization may nonetheless impact adolescent cannabis use. Legalization may affect perceptions of the risk of use (Joffe & Yancy, 2004; Khatapoush & Hallfors, 2004) and the social stigma associated with use (Cruz, Queirolo & Boidi, 2016), increase youth access via third-party purchases (Cerdá et al., 2017), alter illicit market availability (MacCoun, 2011), and/or impact market price (Hall & Weier, 2015). Further, legalization may have an even broader effect on adolescent substance use if it impacts cannabis use and cannabis serves as a substitute or complement to alcohol and other illicit drugs (Cameron & Williams, 2001; Hopfer, 2014; Subbaraman, 2016; Williams, Liccardo Pacula, Chaloupka & Wechsler, 2004).

Unlike cannabis reform legislation in the U.S., which has largely been passed by popular referendum, legalization in Uruguay was enacted by a top-town effort from the president and his ruling party (Walsh & Ramsey, 2015). In fact, at the time of enactment, legalization was opposed by more than 60% of Uruguayans (Cerdá & Kilmer, 2017). By contrast, recent Pew polling data suggests that more than 60% of Americans support legalizing recreational use (Geiger, 2018). The expressed motivation of the legalization of recreational cannabis in Uruguay was to eliminate the illicit drug trade and its associated violence and public health related harms (Cruz et al., 2016; Hudak, Ramsey & Walsh, 2018). Drug possession for personal use had been decriminalized in Uruguay since 1974 (Walsh & Ramsey, 2015).

Uruguay’s law provides for citizens and permanent residents over the age of 18 to legally acquire cannabis by one of three means: (1) home cultivation, (2) cannabis social clubs, or (3) pharmacies. In an effort to discourage problematic use, individuals are only allowed to access one of these three supply mechanisms, and there are limits as to the amounts that may be grown (six plants) or purchased (no more than 10 g per week) (Cerdá & Kilmer, 2017). Uruguay’s law was rolled out in phases, and, importantly for the present study, access through pharmacies only became available in July of 2017. The registry for home-growers began in August of 2014, and cannabis club registration began in October of 2014 (Walsh & Ramsey, 2015). As of November 2018, of an estimated population of 3.5 million people, 31,565 people had registered to purchase in pharmacies (18,110 in Montevideo, the capital city of Uruguay, and 13,455 individuals in the Interior, the other urban regions in the country); 6,980 individuals had registered as home growers (2,101 in Montevideo and 4,879 in the Interior); and 2,831 were members of cannabis clubs (1,326 in Montevideo and 1,505 in the Interior) (Mercado regulado de cannabis Informe V., 2018).

Most of the research on the relationship between cannabis legalization and adolescent cannabis use has focused on the impact of medical marijuana laws (MML) in the United States. Studies have shown that while adolescent use tends to be higher in states that allow medical marijuana (Wall et al., 2011), it does not appear to increase after the passage of MMLs (Choo et al., 2014; Hasin et al., 2015).

More recently, studies have begun to report on the effects of the legalization of recreational cannabis in U.S. states, with mixed findings that offer some indication of increased use among adolescents in some contexts. Using a difference-in-difference approach that compared past 30-day cannabis use among students in Washington and Colorado to students in non-legalizing states before (2010–2012) and after (2013–2015) the passage of the laws, Cerdá et al. (2017) find an increase in past-month cannabis use among 8th and 10th graders following legalization in Washington State, but find no significant impact among 12th graders, and no effect among adolescents of any age in Colorado. A study of legalization in Oregon compared pre and post legalization cohorts of youth and found that there was no effect on the initiation of use, but there was evidence of increased use among youth who were already using cannabis at the time of legalization (Rusby et al., 2018). A more recent study, using household data from all US states (Cerdá et al., 2020), shows no increase in adolescent frequent use, past month or past year cannabis use after the passage of recreational cannabis legalization, although it finds some indication of small increases in cannabis use disorders among adolescent cannabis users.

Section snippets


We compare observed post-intervention cannabis use outcomes in Uruguay to those predicted in the absence of legalization using a generalization of the synthetic control method (SCM) (Abadie & Gardeazabal, 2003; Abadie, Diamond & Hainmueller, 2010; Doudchenko & Imbens, 2016). SCM, rather than using a single control unit or the simple average of control units to estimate a counterfactual time trend for the treated unit in the absence of the treatment, creates a weighted average of a set of


Table 1 shows the weights applied to each Chilean donor region to form the synthetic controls using the pre-legalization data (2001 – 2013, 2003- 2013, 2005 – 2013, 2007–2013). The resulting Mean Squared Prediction Error (MSPE) is shown for each of the outcomes of interest, along with the percentile of the MSPE in the distribution of MSPEs of all the placebo experiments. The weights for the synthetic Uruguay based on pre-intervention (through 2014) trends are shown in the Supplementary


We found the passage and early implementation of recreational cannabis legalization in Uruguay was not associated with changes in the prevalence of adolescent cannabis use or self-reported frequency of use. We did find some indication of an increase in student reports of cannabis availability in the Interior of the country. Given that we did not see a rise in use, this increase, insofar as it is real, may simply represent student perceptions of the new state of affairs post legalization with


The present study provides the first effort to estimate the effect of the first non-commercial model of national cannabis legalization on cannabis use outcomes. As analysts have noted (See e.g., Caulkins & Kilmer, 2016), there is a wide range of potential policies towards cannabis and it should not be viewed as a binary choice between prohibition and for-profit commercial models. It is thus critical that we study and evaluate the different models of legalization and the associated social and

Author contributions

HL supervised the statistical analyses, interpreted the results, and drafted and revised the manuscript. ARA performed the primary statistical analyses, and reviewed and commented on manuscript drafts . AS performed additional statistical analyses and provided statistical consulting. KR provided additional statistical consulting and reviewed and commented on manuscript drafts. ACC, JR, SM reviewed manuscript drafts and provided feedback and comments. MC obtained project funding, guided study

Conflict of Interest Statement



This work was supported by the National Institute on Drug Abuse, R01DA040924-01 (Cerdá).

Research data for this article

Data not available / The authors do not have permission to share data

Further information on research data

References (35)