Does Marijuana Legalization Cause an Increase in Marijuana Use Disorder?

A recent study published in JAMA Psychiatry found that in states enacting recreational marijuana legalization (RML) there may be an increase in frequent marijuana use among adolescents and a higher risk cannabis use disorder (CUD) among adults.

In this survey study, researchers queried 505,796 participants (52% female, 65% white, 12% black, 15% Hispanic) using repeated cross-sectional survey data from the National Survey on Drug Use and Health, which was conducted in the US between 2008-2016 among participants in three different age groups: 12 to 17, 18 to 25, and 26 years or older.

The key endpoint of this study was defined as self-reported past marijuana use, past-month frequent marijuana use, past-month frequent use among past-month users, CUD over the past year, and past-year CUD among past-year users. The researchers used multilevel logistic regression models to estimate the before and after changes in marijuana use among respondents in states who implemented RML and states who did not.

A Potential Public Health Concern

According to the results of the study, past-year CUD increased from 2.18% to 2.72% after RML enactment in the 12 to 17 year age group,  and past-year CUD increased from 2.18% to 2.72% after RML enactment, a 25% higher increase than that for the same age group in states that did not enact RML (OR=1.25; 95% CI, 1.01 to 1.55). The researchers also observed that among past-year marijuana users in this age group, CUD increased from 22.80% to 27.20% (OR=1.27; 95% CI, 1.01 to 1.59).

The findings further showed that unmeasured confounders would need to be more prevalent in RML states and increase the risk of cannabis use by 1.08 to 1.11 times to explain observed results, indicating results that are sensitive to omitted variables. The researchers observed no associations among the respondents aged 18 to 25 years. However, among respondents 26 years or older, past-month marijuana use after RML enactment increased from 5.65% to 7.10% (OR=1.28; 95% CI, 1.16 to 1.40), past-month frequent use from 2.13% to 2.62% (OR=1.24; 95% CI, 1.08-1.41), and past-year CUD from 0.90% to 1.23% (OR=1.36; 95% CI, 1.08 to 1.71). Overall, marijuana users in this age group showed no increase in past-month frequent marijuana uses, and past-year CUD.

“This study’s findings suggest that although marijuana legalization advanced social justice goals, the small post-RML increase in risk for CUD among respondents aged 12 to 17 years and increased frequent use and CUD among adults 26 years or older in this study are a potential public health concern,” the research authors wrote in their conclusion.

They added that “to undertake prevention efforts, further studies are warranted to assess how these increases occur and to identify subpopulations that may be especially vulnerable.”