"Clinicians should routinely assess marijuana use in their patients. Patients who use cannabis, especially heavy users, should be monitored closely, referred for treatment as necessary, and cautioned against their risks of developing drug use disorders," lead investigator Mark Olfson, MD, MPH, New York State Psychiatric Institute, Department of Psychiatry, College of Physicians and Surgeons of Columbia University, New York City, told Medscape Medical News.
"Attitudes toward marijuana, both medical and recreational, have changed a great deal in the last several years, and this new study sounds a note of caution about underappreciated risks linking marijuana use to subsequent development of drug abuse and dependence," added Carlos Blanco, MD, PhD, National Institute on Drug Abuse, Bethesda, Maryland.
The study was published online February 17 in JAMA Psychiatry.
Big Risks
The researchers examined marijuana use and the risk to mental health and for substance use disorders in a nationally representative sample of 34,653 US adults (47.9% male) participating in the National Epidemiologic Survey on Alcohol and Related Conditions. They were interviewed in 2001-2002 (wave 1) and again 3 years later, in 2004-2005 (wave 2).
"What prompted this analysis is the recent increase in marijuana use and abuse in the United States, which have both approximately doubled in the last decade and are likely to increase further in the changing legal environment," Dr Olfson said.
In multiple regression analysis, cannabis use in wave 1, which was reported by 1279 adults, was significantly associated with substance use disorders in wave 2 but not with mood or anxiety disorders.
Table. Odds of Psychiatric Disorders With Cannabis Use
| Disorder | Odds Ratio (95% Confidence Interval) |
| Any substance use disorder | 6.2 (4.1 - 9.4) |
| Any alcohol use disorder | 2.7 (1.9 - 3.8) |
| Any cannabis use disorder | 9.5 (6.4 - 14.1) |
| Any other drug use disorder | 2.6 (1.6 - 4.4) |
| Any nicotine dependence | 1.7 (1.2 - 2.4) |
| Any mood disorder | 1.1 (0.8 - 1.4) |
| Any anxiety disorder | 0.9 (0.7 - 1.1) |
Dr Olfson said he was "somewhat surprised" that there was no increased risk of developing mood and anxiety disorders with cannabis use. "I think it's still possible that had we had a somewhat younger sample we might have found a different profile, because the earliest period of risk of onset of these problems is in early adulthood," he told Medscape Medical News.
Dr Blanco said he was also a "little bit surprised because I was thinking cannabis use was going to affect all disorders, but it seems to be more specific to drug and alcohol disorders."
Although the study cannot establish a causal association between cannabis use and the onset of substance use disorders, "these adverse psychiatric outcomes should be taken under careful consideration in clinical care and policy planning," the authors write in their article.
"Policy makers should step back and consider potential adverse effects of marijuana on the risks of developing drug and alcohol abuse problems. In states with marijuana laws that permit recreational marijuana use, regulators and public health officials should develop means of monitoring and communicating this risk as well as other potential cannabis-related harms," said Dr Olfson.
"We know that marijuana use has been associated with a range of psychiatric disorders, but one of the problems in those studies is that you never know whether the cannabis per se is causing the psychiatric disorders or things like impulsivity to use cannabis, which may also increase the risk of psychiatric disorders independently. In this study, we used statistical techniques to try to isolate the effects of cannabis use," said Dr Blanco.
"The point of the study was to provide objective information to policy makers so they can take into account the risks of cannabis and balance that when they make decisions. From the research that has been done, there is relatively little evidence about the benefits of using cannabis, and this study quite convincingly shows that there are big risks in using cannabis, even at relatively low doses, like once a month."
The study was supported by the Agency for Healthcare Research and Quality and the New York State Psychiatric Institute. The authors report no relevant financial relationships.
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