Legalizing medical marijuana has not increased recreational use of the substance among U.S. adolescents, according to a new study conducted at Columbia University’s Mailman School of Public Health. The findings are published online in the journal Addiction.



“For now, there appears to be no basis for the argument that legalizing medical marijuana has increased teens’ use of the drug,” says Deborah Hasin, PhD, professor of Epidemiology at Columbia’s Mailman School and senior author of the study. “However, we may find that the situation changes as commercialized markets for medical marijuana develop and expand, and as states legalize recreational marijuana use.”



The researchers analyzed the results of eleven separate studies dating back to 1991 using data from four large-scale U.S. surveys: Monitoring the Future, National Longitudinal Survey of Youth, National Survey on Drug Use and Health, and the Youth Risk Behavior Survey. No significant changes, increases, or decreases occurred in adolescent recreational use following enactment of medical marijuana laws.

In 1996, California became the first U.S. state to legalize marijuana use for medical purposes. Medical marijuana is now legal in 29 states. Opponents of medical marijuana have argued that such laws increase recreational marijuana use among adolescents.

Far fewer studies have examined the effects of medical marijuana laws among adults, according to Hasin, who is also a professor in the Department of Psychiatry at Columbia University Medical Center. “Although we found no significant effect on adolescent marijuana use, existing evidence suggests that adult recreational use may increase after medical marijuana laws are passed.” She continues, “The $8 billion cannabis industry anticipates tripling by 2025. Obtaining a solid evidence base about harmful as well as beneficial effects of medical and recreational marijuana laws on adults is crucial given the intense economic pressures to expand cannabis markets.”



Hasin also points out that the intensity of marijuana use in teens has not been explored thoroughly. “This warrants additional consideration, especially with the decreasing national trend of risk perception among adolescents and as the current perception gives rise to more medical marijuana stores and commercial opportunities.”



The first author of the paper is Aaron L. Sarvet. Co-authors are Melanie M. Wall, Katherine M. Keyes, David S. Fink and Emily Greene, Mailman School of Public Health; Aline Le, Columbia University Medical Center; Anne E. Boustead, University of Arizona; Rosalie Liccardo Pacula, Rand Corp.; Magdalena Cerdá, University of California, Davis; and Sandro Galea, Boston University.



The study was supported by the National Institute on Drug Abuse (R01DA034244, R01DA040924, K01DA030449, T32DA031099), National Institute on Alcohol Abuse and Alcoholism (K01AA02151, and by the New York State Psychiatric Institute.

