In an important nationwide study involving more than 34,000 adults, researchers have determined that people who use marijuana are more likely to develop drug or alcohol use disorders than those who do not use the drug. The findings were reported February 17 in the journal JAMA Psychiatry.

Understanding how marijuana use affects mental health is important for informing current debates about the drug's legal status for both medical and recreational use. Earlier studies have found a link between marijuana use and psychotic disorders, including schizophrenia, among those who are genetically vulnerable to the disease. But it has been unclear how marijuana use affects the likelihood that an individual will develop a substance abuse or mood disorder.

To evaluate these relationships, scientists led by NARSAD Distinguished Investigator Mark Olfson, M.D., at Columbia University Medical Center, and including NARSAD 1999 and 2001 Young Investigator Carlos Blanco, M.D., Ph.D., at the National Institute on Drug Abuse and 1989 Young Investigator Deborah S. Hasin, Ph.D., also at Columbia University, turned to data from the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC), a large survey of adults that includes detailed psychiatric information.

During an initial survey, participants in NESARC were asked if they had used marijuana at any time in the last year; 1,279 respondents reported that they had. In a follow-up interview three years later, participants were assessed for specific substance abuse disorders, mood disorders, and anxiety disorders.

When the researchers analyzed the NESARC data, they found no independent association between marijuana use and later development of major depression, bipolar disorder, or anxiety disorders. Use of the drug was, however, associated with an increased incidence of substance abuse disorders. People who reported marijuana use at the outset of the study were more than six times as likely as others to be diagnosed with substance abuse disorders at the three-year follow-up. They were nearly 10 times as likely to have cannabis use disorder, but also significantly more likely to have other drug or alcohol use disorders, including nicotine dependence.

The increased incidence of drug and alcohol use disorders among marijuana users has important consequences for public health, say the researchers, who recommend that policy-makers exercise caution in considering legalizing marijuana for recreational use.