Adolescent Substance Use and Proximal Risk Factors in the Context of Changes in Medical Marijuana Legislation in Washington State

Background

Emerging state-level legalization of marijuana for medical and recreational use has raised concerns that such legislation may lead to more favorable attitudes and norms, lower perception of harm among youth, and subsequent increases in marijuana and other substance use among adolescents. However, studies on the effects of medical marijuana legislation (MML) on adolescent marijuana use yielded mixed results. Few studies have examined the effects of MML on other substance use and none has systematically evaluated changes in proximal risk factors, such as perceptions of harm, before and after MML. This study examines changes in adolescent substance use and proximal risk factors for substance use before and after the passage of MML that occurred in WA in November 1998.

Methods and Results

Data come from biennial cross-sectional surveys of students in grades 6, 8, 10, and 12 across Washington State collected from Spring 1998 through Spring 2004 (average N=21,855 per year) as a part of the collaborative effort between the state agencies and the 6-state and Diffusion projects. Proximal risk factors included students’ perceptions of harm from substance use and laws and social norms favorable to drug use. The substance use outcomes included prevalence of past month marijuana, alcohol, and tobacco use.

Preliminary analyses using cross-classified fixed effects models stratified by grade and controlling for gender revealed no increase in substance use over time. In fact, the prevalence of past month marijuana as well as alcohol and tobacco use was significantly higher in the spring of 1998 than at any of the post-MML time points for each of the four grades, and the perceived harm from marijuana use was higher in the years after MML than before. However, there was some evidence of an increase in prevalence of those indicating being unsure about harmfulness of marijuana use at the time point immediately after MML, but this trend was reversed in the following years. Next steps in the analyses will include (1) examination of changes in additional risk factors such as the youth’s perceived availability of marijuana; and (2) systematic examination of the precision of estimates as related to the inclusion of additional pre- and post-MML time-points and additional control variables such as race/ethnicity.

Conclusions

This study is the first to comprehensively evaluate changes in substance use as well as proximal risk factors among youth before and after passage of MML in WA. The limitations of the study as well as the implications of these findings for prevention efforts aimed at decreasing adolescent substance use will be discussed.