This article is more than 5 years old. Information may no longer be current.

Medical marijuana laws do not increase adolescent use of marijuana

Results from multiple annual cross-sectional surveys indicate that passing state medical marijuana laws did not increase marijuana use among adolescents, although adolescent use is higher in states with medical marijuana laws.

“Although the specific provisions of state medical marijuana laws differ, they all have a common purpose: to legalize the use of marijuana for medical purposes. However, by conveying a message about acceptability or an absence of harmful health consequences, passage of such laws could affect youth perception of harms, leading to increased prevalence of marijuana use,” study researcher Deborah S. Hasin, PhD, of Columbia University’s Mailman School of Public Health, and colleagues wrote in Lancet Psychiatry.

Deborah S. Hasin

To assess associations between state medical marijuana laws and adolescent marijuana use, researchers analyzed data from 1,098,270 adolescents who completed annual national surveys administered to students in eighth, tenth and twelfth grades from 1991 through 2014.

Marijuana use within the past 30 days was more common in states that passed medical marijuana laws than those that did not (15.87% vs. 13.27%; P = .0057).

Risk for marijuana use did not significantly change after passage of medical marijuana laws (16.25% pre-law vs. 15.45% post-law).

However, the association between grade and risk before and after passage of medical marijuana laws was significant (P = .001): Marijuana use significantly decreased among eighth-graders after passage of medical marijuana laws, but did not among tenth- and twelfth-graders.

Risk for adolescent marijuana use pre- and post-passage varied from state to state, as did the interaction between grade and effects of medical marijuana laws.

“The results of this study showed no evidence for an increase in adolescent marijuana use after passage of state laws permitting use of marijuana for medical purposes,” Hasin and colleagues wrote. “Whether access to a substance for medical purposes should be determined by legislation rather than biomedical research and regulatory review is debatable.”

Kevin P. Hill

According to Kevin P. Hill, MD, MHS, of McLean Hospital, the importance of scientific research is strengthened by these study findings.

“This study draws attention to the importance of undertaking rigorous scientific research to test hypotheses and using the results to develop sensible health policies,” Hill wrote in an accompanying editorial. “Policies might sometimes be shaped by preconceived notions that do not end up being true, and Hasin and colleagues’ study is an example of such an occurrence… The growing body of research that includes this study suggest that medical marijuana laws do not increase adolescent use, and future decisions that states make about whether not to enact medical marijuana laws should be at least partly guided by this evidence.” – by Amanda Oldt

Disclosure: Hasin and colleagues report no relevant financial disclosures. Hill reports financial ties with NIDA and Hazelden Publishing.