The Effect of Medical Marijuana Laws on Drug Use by Adolescents

An interesting study in the February 1, 2018 issue of Drug and Alcohol Dependence suggests that medical marijuana laws led to a decline in use of marijuana and other substances by 8th graders, had no effect on 10th graders, and increased usage among 12th graders.

Background

Historical shifts have taken place in the last twenty years in marijuana policy. The impact of medical marijuana laws (MML) on use of substances other than marijuana is not well understood. We examined the relationship between state MML and use of marijuana, cigarettes, illicit drugs, nonmedical use of prescription opioids, amphetamines, and tranquilizers, as well as binge drinking.

Methods

Pre-post MML difference-in-difference analyses were performed on a nationally representative sample of adolescents in 48 contiguous U.S. states. Participants were 1,179,372?U.S. 8th, 10th, and 12th graders in the national Monitoring the Future annual surveys conducted in 1991–2015. Measurements were any self-reported past-30-day use of marijuana, cigarettes, non-medical use of opioids, amphetamines and tranquilizers, other illicit substances, and any past-two-week binge drinking (5+ drinks per occasion).

Results

Among 8th graders, the prevalence of marijuana, binge drinking, cigarette use, non-medical use of opioids, amphetamines and tranquilizers, and any non-marijuana illicit drug use decreased after MML enactment (0.2–2.4% decrease; p-values:?<0.0001–0.0293). Among 10th graders, the prevalence of substance use did not change after MML enactment (p-values: 0.177–0.938). Among 12th graders, non-medical prescription opioid and cigarette use increased after MML enactment (0.9–2.7% increase; p-values: <0.0001–0.0026).

Conclusions

MML enactment is associated with decreases in marijuana and other drugs in early adolescence in those states. Mechanisms that explain the increase in non-medical prescription opioid and cigarette use among 12th graders following MML enactment deserve further study.