No uptick in marijuana use by adolescents after states pass medical marijuana laws

October 19, 2016 — Adults over the age of 25 increased their use of marijuana after their home states made changes to medical marijuana laws, according to new research by scientists at Columbia University's Mailman School of Public Health. However, there was no difference in the prevalence of marijuana use reported for 12 to 17 or 18 to 25 year-olds after the laws passed. The findings are published online in the journal Drug and Alcohol Dependence.

The study is the first to link state medical marijuana laws with marijuana availability and use among adults. Results were based on 10 years of annual survey data from respondents to the National Survey of Drug Use and Health.

Until now there had been little information on how perceived availability is associated with marijuana use among the general population and, in particular, for adults, who are the majority of licensed medical marijuana users. Because medical marijuana laws are largely intended for older patients who suffer from illnesses such as chronic pain or cancer, it was considered likely that medical marijuana laws affect different age groups differently, and through different modes of access.

"While the evidence had suggested there is a link between the passage of laws and increases in marijuana use by those 21 and older, it was not clear if all sub-groups of adults were influenced in the same way," said Silvia Martins, MD, PhD, associate professor of Epidemiology. "Before medical marijuana laws changed there was a concern that this type of legislation could potentially increase recreational marijuana use in adolescents and adult populations. At least for now, we do not see an increase in use among adolescents."

The study found that adults 26 years and older increased their past-month use of marijuana from 5.87 percent to 7.15 percent after medical marijuana laws had passed in their state.

In addition to increasing marijuana use among those 26 years of age and older, the perceived availability of marijuana also increased after the laws were passed. And for all age groups, the perception that marijuana became easily available was higher in states that had passed medical marijuana laws by 2013. However, similar to marijuana use, there was no effect of medical marijuana laws on a change in perception of availability of marijuana among adolescents (ages 12 to 17) or young adults (ages 18 to 25) but there was a significant increase in perceiving marijuana as easily available among those 26 and older, from 59 percent to 62 percent.

According to Dr. Martins, while not all states with medical marijuana laws have enforced patient registration, the number of patients registered in medical marijuana programs have increased over time in those states, particularly after 2009 when there were substantial changes in federal prosecution laws regarding marijuana cultivation, distribution, and possession.

"Understanding how the passage of medical marijuana laws affects different age groups improves our understanding of the effects of marijuana policies and provides information about the types of public health responses that should accompany major policy changes related to marijuana," said Martins.

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Co-authors are Christine M. Mauro, Julian Santaella-Tenorio, June H. Kim, Katherine M. Keyes, Deborah S. Hasin, and Melanie Wall, all of Columbia University's Mailman School of Public Health; Magdalena Cerda, University of California, Davis; and Sandro Galea, Boston University.

This study was supported by the National Institutes of Health, National Institute on Drug Abuse (NIH-NIDA) (grants R01 DA037866, R01 DA034244, K01DA030449 and T32 DA031099); National Institutes of Health, National Institute of Alcohol and Alcoholism (NIH-NIAAA) (grant K01AA021511). Dr. Santaella is funded by the J. William Fulbright and the Colciencias doctoral scholarships. Dr. Hasin is funded by the New York State Psychiatric Institute. The authors have no conflicts of interest.

Columbia University's Mailman School of Public Health

Founded in 1922, Columbia University's Mailman School of Public Health pursues an agenda of research, education, and service to address the critical and complex public health issues affecting New Yorkers, the nation and the world. The Mailman School is the third largest recipient of NIH grants among schools of public health. Its over 450 multi-disciplinary faculty members work in more than 100 countries around the world, addressing such issues as preventing infectious and chronic diseases, environmental health, maternal and child health, health policy, climate change & health, and public health preparedness. It is a leader in public health education with over 1,300 graduate students from more than 40 nations pursuing a variety of master's and doctoral degree programs. The Mailman School is also home to numerous world-renowned research centers including ICAP (formerly the International Center for AIDS Care and Treatment Programs) and the Center for Infection and Immunity. For more information, please visit http://www.mailman.columbia.edu.

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