Illicit cannabis use and cannabis use disorders increased at a greater rate in states that passed medical marijuana laws than in other states, according to new research at Columbia University's Mailman School of Public Health and Columbia University Medical Center. The findings will be published online in JAMA Psychiatry.
Laws and attitudes regarding cannabis have changed over the last 20 years. In 1991, no Americans lived in states with medical marijuana laws, while in 2012, more than one-third lived in states with medical marijuana laws, and fewer view cannabis use as entailing any risks.
The new study is among the first to analyze the differences in cannabis use and cannabis use disorders before and after states passed medical marijuana laws, as well as differentiate between earlier and more recent periods and additionally examine selected states separately.
The researchers used data from three national surveys collected from 118,497 adults: the 1991-1992 National Longitudinal Alcohol Epidemiologic Survey, the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions and the 2012-2013 National Epidemiologic Survey on Alcohol and Related Conditions-III.
Overall, between 1991-1992 and 2012-2013, illicit cannabis use increased significantly more in states that passed medical marijuana laws than in other states, as did cannabis use disorders. In particular, between 2001-2002 and 2012-2013, increases in use ranged from 3.5 percentage points in states with no medical marijuana laws to 7.0 percentage points in Colorado. Rates of increase in the prevalence of cannabis use disorder followed similar patterns.
"Medical marijuana laws may benefit some with medical problems. However, changing state laws -- medical or recreational -- may also have adverse public health consequences, including cannabis use disorders," said author Deborah Hasin, PhD, associate professor of Epidemiology at the Mailman School of Public Health and in the Department of Psychiatry at Columbia University Medical Center. "A prudent interpretation of our results is that professionals and the public should be educated on risks of cannabis use and benefits of treatment, and prevention/intervention services for cannabis disorders should be provided."
While illicit use of marijuana decreased and marijuana use disorder changed little between 1991-1992 and 2001-2002, both use and disorder rates increased between 2001-2002 and 2012-2013. In 1991-1992, predicted prevalences of use and disorder were higher in California than other states with early-medical marijuana laws (use: 7.6 percent vs. 4.5 percent; disorder: 2 percent vs. 1.15 percent). However, the predicted prevalence of past year use in California did not differ significantly from states that passed laws more recently. In contrast, the prevalences of use and disorder increased in the other 5 states with early medical marijuana laws.
"Future studies are needed to investigate mechanisms by which increased cannabis use is associated with medical marijuana laws, including increased perceived safety, availability, and generally permissive attitudes," Dr. Hasin also noted.
Co-authors: Aaron Sarvet and Malka Stohl, Columbia University Medical Center; Katherine Keyes and Melanie Wall, Mailman School of Public Health; Sandro Galea, Boston University School of Public Health; and Magdalena Cerda, University of California, Davis.
The study was supported by the National Institute on Alcohol Abuse and Alcoholism (grant K01AA021511), National Institutes of Health (R01DA034244, National Institute on Drug Abuse (grants K01AA021511, R01Dao40924-01A), and the New York State Psychiatric Institute.
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.
Columbia University Department of Psychiatry Columbia Psychiatry is ranked among the best departments and psychiatric research facilities in the nation and has contributed greatly to the understanding and treatment of psychiatric disorders. Located at the Columbia University Medical Center campus in Washington Heights, the department enjoys a rich and productive collaborative relationship with physicians in various disciplines at Columbia University's College of Physician's and Surgeons. Columbia Psychiatry is home to distinguished clinicians and researchers noted for their clinical and research advances in the diagnosis and treatment of depression, suicide, schizophrenia, bipolar and anxiety disorders, eating disorders, and childhood psychiatric disorders. Visit http://columbiapsychiatry.org for more information.