Legal Marijuana Making Roads Less Safe?

Megan Brooks

May 29, 2014

Since Colorado legalized medical marijuana in 2009, there has been an increase in the number of drivers involved in fatal motor vehicle crashes who test positive for marijuana, a new federally funded study shows.

"I think that this raises very important concerns," study investigator Stacy Salomonsen-Sautel, PhD, of the Department of Psychiatry, University of Colorado, in Aurora, told Medscape Medical News. "There is definitely a need for better education and prevention programs" to prevent marijuana-impaired driving," she added.

The study was published online April 23 in the journal Drug and Alcohol Dependence.

Lack of Research

Legal medical marijuana has been commercially available in Colorado since mid 2009. Yet, little is known about the impact of marijuana commercialization on impaired driving.

The investigators analyzed data from the 1994 to 2011 Fatality Analysis Reporting System, which tracks fatal car crashes in the United States.

They noticed an upward trend in Colorado in the proportion of drivers in a fatal motor vehicle crash who tested positive for marijuana since mid 2009 (change in trend, 2.16; P < .0001).

This coincides with a "large increase in registered medical marijuana users in the middle of 2009, and a lot of medical marijuana dispensaries opened around that time," Dr. Salomonsen-Sautel noted. In contrast, there was no significant change in 34 states that had no medical marijuana laws.

The authors note that the proportion of drivers in a fatal motor vehicle crash who tested positive for marijuana in Colorado was decreasing during the premarijuana commercialization period but that it now seems to be increasing.

For Colorado and for nonmedical marijuana states, no significant changes were seen in the proportion of drivers in a fatal motor vehicle crash who were alcohol impaired.

Dr. Salomonsen-Sautel emphasized that this study cannot determine a cause and effect relationship between the marijuana use and the vehicle accidents. However, research shows that both alcohol and marijuana impair driving.

APA Position

Reached for comment, Didier Jutras-Aswad, MD, a psychiatrist with the University of Montreal, in Quebec, Canada, said that although the study underlines trends that may be useful in conducting other more detailed, focused research, it does not allow for "any definitive conclusions about causal effect between any exposure/factor ― that is the change in cannabis legal status ― and an outcome."

"This study simply suggests that more well-designed research is needed on the impact of cannabis legalization/use," he told Medscape Medical News.

Regarding state initiatives to authorize the use of marijuana for medical purposes, the American Psychiatric Association (APA) notes in a position statement that medical treatment "should be evidence-based and determined by professional standards of care; it should not be authorized by ballot initiatives. Marijuana that is dispensed under a state-authorized program is not a specific product with controlled dosages. The buyer has no way of knowing the strength or purity of the product, as cannabis lacks the quality control of FDA-approved medicines."

"Prescribers and patients should be aware that the dosage administered by smoking is related to the depth and duration of the inhalation, and therefore difficult to standardize. The content and potency of various cannabinoids contained in marijuana can also vary, making dose standardization a challenging task. Physicians who recommend use of smoked marijuana for 'medical' purposes should be fully aware of the risks and liabilities inherent in doing so," the APA statement adds.

The study was supported by the National Institute on Drug Abuse and the National Institute on Alcohol Abuse and Alcoholism. The authors have disclosed no relevant financial relationships.

Drug Alcohol Depend. Published online April 23, 2014. Abstract

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