Medical Marijuana Laws Spark Uptick in Illicit Cannabis Use

Megan Brooks

April 27, 2017

Illicit cannabis use and cannabis use disorders have increased more in states that passed medical marijuana laws than in those that did not, according to an analysis of national survey data.

"Medical marijuana laws may benefit some with medical problems. However, changing state laws (medical or recreational) may also have adverse public health consequences," write the authors, led by Deborah Hasin, PhD, of Columbia University Medical Center in New York City.

Laws and attitudes regarding cannabis have changed during the past 20 years. In 1991-1992, no Americans lived in states with medical marijuana laws, whereas in 2012, more than one third lived in states with medical marijuana laws, and fewer view marijuana as risky, they note.

Dr Hasin and colleagues analyzed data collected from 118,497 adults who took part in three national surveys on drug and alcohol use that were conducted in 1991-1992, 2001-2002, and 2012-2013.

They found that from 1991-1992 to 2012-2013, illicit cannabis use increased significantly more in states that had passed medical marijuana laws than in other states (1.4 percentage points more, P = .004), as did cannabis use disorders (0.7 percentage point more, P = .03).

In states without medical marijuana laws, the average prevalence of illicit cannabis use was 4.54% in 1991-1992 and 6.70% in 2012-2013. By comparison, in states with medical marijuana laws, the prevalence of illicit use jumped from 5.55% in 1991-1992 to 9.15% in 2012-2013.

A similar pattern was seen for cannabis use disorder. The average prevalence went from 1.35% in 1991-1992 to 2.30% in 2012-2013 in states without medical marijuana laws, and from 1.48% to 3.10% in states that did legalize medical marijuana.

"Holding population size and demographic distributions constant from 1991 to 2012, an additional 1.1 million adult illicit cannabis users and an additional 500,000 adults with a DSM-IV-diagnosed cannabis disorder may be attributable to medical marijuana law passage," the investigators note.

The study was published online April 26 in JAMA Psychiatry.

New Reality

"Americans increasingly see marijuana as a harmless substance. While some can use marijuana without harm, it does have some risks, including the risk for cannabis use disorder and its symptoms," Dr Hasin told Medscape Medical News.

"The public should take this into account when making personal decisions about use, and when voting on new marijuana laws. Health providers should take this into account when working with patients. Policy makers should take this into account when considering new legislation so that if new laws are passed, the laws can incorporate regulations to reduce the likelihood of unintended health consequences from increased use," said Dr Hasin.

The researchers say future studies are needed to determine the reasons for the association between medical marijuana laws and increased cannabis use.

"Our study wasn't designed to answer this question, but reasonable explanations are that medical marijuana laws could convey to the public that marijuana is safe and acceptable, and that a proliferation of dispensaries and advertising could further normalize marijuana use and possibly increase diversion of marijuana," said Dr Hasin.

In an accompanying editorial, Wilson M. Compton, MD, deputy director of the National Institute on Drug Abuse (NIDA), and colleagues say the analysis confirms two earlier reports linking changes in medical marijuana laws to increases in cannabis use and disorders in adults.

"Understanding the nuances of the laws to determine which components of a policy are associated with positive and negative effects and to balance potential harms and benefits should be necessary considerations for policymakers and those implementing state laws," write Dr Compton and colleagues.

"While research continues to gather evidence to that end, clinicians are faced with the reality reinforced by the findings from Hasin et al that cannabis use is increasing among adults living in states that have legalized medical marijuana," they add.

"In the meantime, it is clear that a robust system of education, prevention, and treatment is needed to minimize the negative consequences that might arise if cannabis use continues to increase," the authors conclude.

The research was funded by NIDA and the National Institute on Alcohol Abuse and Alcoholism. The authors have disclosed no relevant financial relationships.

JAMA Psychiatry. Published online April 26, 2017. Full text, Editorial

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