Medical marijuana laws not linked to an increase teen marijuana use

1. In states that passed a medical marijuana law at any time before 2014, there was a higher prevalence of marijuana use among adolescents within the previous 30 days than in states that had not passed medical marijuana laws.

2. In states that passed medical marijuana laws, there was not a significant difference in the risk of marijuana use in adolescents before passing medical marijuana laws compared to after passing the laws.

Evidence Rating Level: 3 (Average)

Study Rundown: The relationship between laws permitting medical marijuana use and marijuana use in adolescents is frequently debated. This study used national data to examine the relationship between adolescent use of marijuana and state medical marijuana laws. Data was collected for 24 years by administering a self-administered questionnaire on marijuana use to more than one million 8th, 10th, and 12th-grade students in nearly 400 schools across the United States. This study sought to assess if marijuana use was higher overall in states that had passed a medical marijuana law before 2014, and if the risk of marijuana use changed after the passage of medical marijuana laws.

The results showed that in states that had passed a medical marijuana law at any time until 2014, the prevalence of marijuana use in adolescents was higher than in states that had not passed any medical marijuana laws. However, in states that passed medical marijuana laws, there was not a significant increase in the risk of marijuana use among adolescents after passing the laws compared to before the laws were passed. This study was strengthened by its large sample size and the comprehensive analysis across a long time-span, however, variations in individual state laws were not examined, and some states had only recently passed medical marijuana laws before this study was conducted.

Click to read the study in The Lancet Psychiatry

Relevant Reading: Effects of State Medical Marijuana Laws on Adolescent Marijuana Use

In-Depth [cross-sectional study]: This study was based on data collected in annually repeated cross-sectional surveys. The Monitoring the Future study instrument is a self-administered questionnaire conducted annually since 1991 by 8th, 10th, and 12th-grade students across the US (modal ages 13-14, 15-16, and 17-18 years, respectively). The primary outcome of the study was any marijuana use in the past 30 days, and the secondary outcome was whether or not the risk of marijuana use in adolescents changed after the passage of medical marijuana laws. Co-variables for individual, school, and state-level characteristics were controlled for in the study.

1,098,270 adolescents in 48 states were surveyed between 1991 and 2014. The results showed that in states that had passed a medical marijuana law any time up to 2014, there was a higher prevalence of marijuana use among adolescents within the previous 30 days than in states that had not passed medical marijuana laws (adjusted prevalence 15.87% vs. 13.27%; adjusted odds ratio [OR] 1.27, 95% CI 1.07-1.51; p=0.0057). However, in states that passed medical marijuana laws, there was not a significant difference in the risk of marijuana use in adolescents before passing medical marijuana laws compared to after passing the laws (adjusted prevalence 16.25% vs. 15.45%; adjusted OR 0.92, 95% CI 0.82-1.04; p=0.185).

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