March 16, 2016--The percentage of Americans who reported using marijuana in the past year more than doubled between 2001-2002 and 2012-2013, and the increase in marijuana use disorders during that time was nearly as large, according to a new study in the American Journal of Psychiatry. The research also showed that 2.5 percent of adults--nearly 6 million people--experienced marijuana use disorder in the past year, while 6.3 percent had met the diagnostic criteria for the disorder at some point in their lives.

The collaborative study was carried out by scientists at Columbia University's Mailman School of Public Health, Columbia University Medical Center, and the National Institute on Alcohol Abuse and Alcoholism (NIAAA), part of the National Institutes of Health.

The study also found that marijuana use disorder is often associated with other substance use disorders, behavioral problems, and disability, and goes largely untreated.

The data were collected in the 2012-2013 wave of NIAAA's National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), the largest ever conducted on the co-occurrence of alcohol use, drug use, and related psychiatric conditions. For this study, over 36,000 U.S. adults were interviewed about alcohol, drug, and related psychiatric conditions. The data showed that marijuana use disorder is about twice as common among men than women, that younger age groups are much more likely to experience the disorder than people age 45 and over, and that those at the lowest income levels were at the highest risk.

This is the first national survey to use the diagnostic criteria from Diagnostic and Statistical Manual of Mental Disorders (DSM-5). In DSM-5, the old categories of marijuana dependence and abuse are combined into a single disorder. To be diagnosed with the disorder, individuals must meet at least two of 11 symptoms that assess craving, withdrawal, lack of control, and negative effects on personal and professional responsibilities. Severity of the disorder is rated as mild, moderate, or severe depending on the number of symptoms. As the severity of marijuana use disorder increased, so did associated disability levels and frequency of marijuana use.

Deborah Hasin, PhD, lead author and professor of epidemiology in the Department of Psychiatry at CUMC with a joint appointment in the Columbia University Mailman School of Public Health Department of Epidemiology, was on the workgroup responsible for making the changes in DSM-5 substance use diagnostic criteria, including marijuana use disorders. In a study published last year, Dr. Hasin reported that three out of 10 marijuana users experienced marijuana abuse or dependence in 2012-13.

"An increasing number of American adults do not perceive marijuana use as harmful," said Hasin. "While some can use marijuana without harms, other users do experience negative consequences, which can include mental and physical problems, and impaired functioning. This paper helps provide information on some of those risks."

The researchers found that only about 7 percent of people with past-year marijuana use disorder receive any marijuana-specific treatment, and only about 14 percent of people with lifetime marijuana use disorder receive treatment.

"The new analysis complements previous population-level studies conducted by the National Institute on Alcohol Abuse and Alcoholism that show marijuana use can lead to harmful consequences for individuals and society," said George F. Koob, PhD, director of NIAAA.

"These findings demonstrate that people with marijuana use disorder are vulnerable to other mental health disorders," said Nora D. Volkow, MD, director of the National Institute of Drug Abuse (NIDA), which contributed funding to the study. "The study emphasizes the need for such individuals to receive help through evidence-based treatments that address these co-occurring conditions."

The study authors note the urgency of identifying and implementing effective prevention and treatment for marijuana use disorder and call for more research to understand the combined effects of marijuana and alcohol. "We feel strongly that more public education about the dangers associated with marijuana use is imperative," stated Hasin. "This is especially critical since we are learning more about public beliefs that marijuana use is harmless."