Education efforts about the adverse impact marijuana use can have on depression are needed, with a focus on subgroups at risk for poor outcome. Together, our results warrant replication and indicate a need for providers to ask depressed patients about their marijuana use, to inform those using marijuana of its potential risks and determine treatment needs. Patients were participants in a randomized controlled trial of alcohol and drug use among psychiatry outpatients and had PHQ-9 depression of ≥ 5, limiting generalizability. Patients were using substances other than marijuana, limiting our ability to draw firm conclusions, although all models adjusted for non-marijuana use. Models were unadjusted for patient’s premorbid functioning/marijuana use, which could have impacted the results. Substance use variables were dichotomized due to low frequency, reducing statistical power, our ability to determine quantity/frequency, and our understanding of patterns over time. We do not know how patients used marijuana , whether problems were associated with use, or the primary reason/condition for medical use. Longitudinal analyses are limited to a 6-month follow-up, suggesting further research will be needed over longer periods of time. Marijuana is the most widely used controlled substance in the world . In 2016, 192.2 million people used marijuana . Regular marijuana use, particularly initiated in adolescence, is associated with a range of adverse consequences,grow benches including poor cognitive and educational outcomes, low self-reported life satisfaction , downward socioeconomic mobility , psychiatric illness , marijuana-involved injury , and substance use disorders .
Perceived risk and perceived availability of marijuana have historically been important drivers of adolescent marijuana use, and often targets of interventions to prevent or reduce adolescents’ use . However, these relationships may be changing. Most extant research on the changing associations between adolescent perceived risk, availability, and use of marijuana has been conducted in the United States , where 28 states and the District of Columbia have legalized medical marijuana since 2000, and 10 states and DC have legalized recreational marijuana since 2012 . In this context, more adolescents now perceive no/low risk of marijuana use, but the prevalence of marijuana use has not increased simultaneously . Research on changes in the individual-level association between no/low perceived risk and use has been mixed. Some have found that the association weakened in recent years , while others have reported that it strengthened or remained stable . Additionally, perceived easy availability of marijuana has largely declined among US adolescents . Evidence suggests that the association between perceived availability and use of marijuana has remained strong and stable over time . Understanding these relationships is particularly important in light of recent liberalization of marijuana access, as perceived risk and availability are two key mechanisms through which legalization could impact use. In this study, we focus on the Southern Cone context for two reasons. First the Southern Cone has recently experienced changes in marijuana regulation, which could impact perceived risk and availability. Second, trends in adolescent marijuana use and perceived availability are different from those in the US, which could suggest distinct relationships between perceived risk and availability and use of marijuana. In 2013, Uruguay enacted a law providing the government full regulation over the largescale production and sale of recreational marijuana.
Adults in Uruguay can purchase marijuana at pharmacies, grow marijuana at home, or acquire it through a cannabis club . In Argentina, possession of marijuana for personal use continues to be illegal ; however, a 2009 court judgment marked the beginning of a paradigm shift in the criminalization of marijuana since it raised a contradiction between Law 23,737 and Article 19 of the Constitution, which protects individuals’ freedom from state regulation . In 2017, Argentina approved access to medical marijuana under specific circumstances . In Chile, marijuana is decriminalized, a limited set of cannabis-based pharmaceutical products are available for medical use, and a new bill allowing other sources of access and formulations is under debate . Since the early 2000’s, past-month adolescent marijuana use has increased in Uruguay , Chile , and Argentina . These trends are distinct from the US where marijuana use has remained stable , and from other South American countries where past-year use is less than 5% . Although perceived risk of marijuana use has decreased in both the Southern Cone and the US, perceived availability has increased in the Southern Cone, but decreased in the US . We know of no study that has assessed the individual-level relationships between adolescent perceived risk, availability, and use of marijuana in the context of the Southern Cone. Such research may inform the priority and scope of context-specific public health interventions to prevent adolescent marijuana use and help identify the drivers of use during these historical shifts. As more regions debate or enact policies to decriminalize or legalize marijuana use, the impetus for cross-country comparisons increases. In this study, we used survey data from adolescents in Argentina, Chile, and Uruguay to 1) estimate associations between perceived availability and perceived risk of marijuana use and past-month marijuana use, and 2) describe how these associations changed over time.
Individual-level data from adolescents enrolled in secondary education in Uruguay, Chile, and Argentina were obtained from the National Surveys on Drug Use Among Secondary School Students . These cross sectional surveys, carried out every 2–3 years, collect information on substance use and related risk factors. The sampling design and survey instruments are similar to the Monitoring the Future Surveys and were implemented comparably across countries. Surveys were self-report and administered confidentially in students’ classrooms. The sample included 8th, 10th, and 12th graders in schools classified as public, private, and other in mostly urban areas. Net secondary school enrollment was 80–90% in Chile and Argentina over the last decade and increased from 67.6–82.8% from 2007 to 2016 in Uruguay . The sample was selected via clustered, multistage random sampling from areas with 10,000+ and 30,000+ inhabitants in Uruguay and Chile, respectively, and schools with at least 20 students in the grades under study in Argentina. In Uruguay and Argentina, strata were types of school within urban areas of geographical regions in each country; primary sampling units were schools followed by classrooms. In Chile,grow racks with lights strata were school type by grade within mostly urban areas and primary sampling units were classrooms. Individual-level survey weights were used. Recent school cooperation rates ranged from 76–86%. This study was determined not human subjects research by the University of California, Davis Institutional Review Board. We restricted the sample in two ways. First, we removed adolescents with poor quality data [i.e. those who responded “yes” to any past-month use of five or more illicit substances , lifetime users of a fictional drug, and those with more than four inconsistencies in reporting age of initiation of use, past month, past year, and lifetime use of marijuana] based on criteria used in Uruguay before data entry. To maintain comparability, we removed observations in Chile and Argentina based on the same criteria. Second, we restricted the sample to the years our variables of interest were collected. Analyses were done in Stata 15.1 and SAS 9.4 and conducted separately per country. We used the svy suite in Stata for descriptive analyses and weighted time-varying effect modeling in the SAS macro %Weighted TVEM to estimate odds ratios for past-month marijuana that vary smoothly over time, accounting for the complex survey design . This method, made available in 2017 with the %Weighted TVEM macro, uses unpenalized B-splines to estimate coefficients and point-wise 95% confidence intervals as continuous functions over time, thus relaxing parametric assumptions about how the relationships between perceived risk, availability and marijuana use vary over time, and allowing for non-linearity . TVEM has been used to assess historical trends in the US in associations between adolescent marijuana use and related attitudes .
TVEM models were run on each imputed data set, and then estimates and standard errors were combined with the PROC MIANALYZE procedure in SAS. For each country and analytic sample, we present bivariate TVEM results. Graphs are shown with consistent x-axes , but different y-axes per country to aid interpretation. Because of the small sample sizes given the relatively low prevalence of marijuana use, our ability to adjust for covariates was limited. When possible, we adjusted for grade and gender, alcohol use, and tobacco use. Additionally, in Chile, the only country with enough observations and overlapping years of data to run TVEM models, we also included risk and availability simultaneously. For this analysis, we used a separate imputation model that included both variables in the same process. All covariates were time-varying. Finally, to better understand trends in the relationships between perceptions and use, we examined how the prevalence of marijuana use changed over time within each level of perceived risk and availability.Across countries and years, approximately 5–10% of adolescents reported past-month marijuana use, with greater prevalence in Chile followed by Uruguay . Marijuana use generally increased over time , and there was a notable increase in use among Chilean adolescents from 2009–2013 . On average, approximately 7–25% of adolescents perceived no/low risk of regular marijuana use, with greater prevalence in Chile followed by Uruguay . The proportion of adolescents who perceived marijuana to pose no/low risk increased over the study period despite year-to-year fluctuations . In Chile, there was a large increase in the proportion of adolescents who perceived no/low risk from 2011–2013, in addition to greater overall change and yearly variation, compared to Argentina and Uruguay, where the prevalence increased to a lesser degree with less variation . On average, one-third to one-half of adolescents perceived marijuana to be easily available, with greater prevalence in Uruguay followed by Chile . Trends varied over time . In Argentina, perceived availability increased from 2005 to 2009–2011 and then decreased or plateaued until 2014 . In Chile, perceived availability of marijuana generally declined from 2001 to 2009–2011 and increased thereafter . In Uruguay, perceived availability increased from 2005 to 2007–2009, plateaued or declined slightly until 2011, then increased until 2016 . Consistent with prior studies from South America and the US, our results indicate that the less risk an individual attributes to marijuana use, the more likely he/she is to use marijuana . However, in the Southern Cone countries, the overall magnitude of this association weakened, although it strengthened again most recently in Argentina. This suggests that risk perceptions became a weaker correlate of adolescent marijuana use over time. There are several implications of these results. First, given the overall increase in the proportion of adolescents who perceive marijuana use to pose no/low risk of harm, marijuana use would have likely increased to a greater degree in the Southern Cone had the risk/use relationship not weakened. Second, factors other than risk perceptions, such as marijuana availability, may have played a greater role in the increase in adolescent marijuana use observed during our study period. This highlights the need to consider changes in multiple individual and environmental determinants of marijuana use. Third, there may be a cross-national weakening of the risk/use relationship. We found this trend in all Southern Cone countries, and some have identified the weakening of this relationship in the US as well . This would suggest that risk perceptions may be, at least in part, shaped by broader societal norms that extend beyond local or national context. Increases in global information sharing via internet use, social media, and international news coverage may contribute to this trend . Consistent with extant research in Europe and the US , we found that adolescents who perceive marijuana to be easily available are more likely to use marijuana. However, the stability of this association varied over time and between countries. In Chile, the availability/use association weakened, and became increasingly similar to the risk/use association, both in magnitude and trajectory, when risk and availability were modeled together. In contrast, the relationship between availability and use strengthened in Argentina and Uruguay, becoming stronger at times than the relationship between perceived risk and use in both countries. However, because we were not able to model both variables together in Argentina and Uruguay due to finite sample limitations, it is unclear how the associations relate to one another. Variation in the relationship between perceived availability and use of marijuana over time and between countries may be explained by several factors.