REPLY FROM: The Authors of The Study....

There is no arguing with the fact that driving fatalities resulting from substance impairment is a critical public health issue. However, I feel that some of your comments as they relate to our study are off base.

First, our methods are quite rigorous, and much detail is provided in the narrative. Our multiple time series design is considered by many (e.g., Campbell) to be one of the strongest research designs in the social sciences when an experiment is not feasible, as is the case here. Perhaps more important, our focus was on "medical marijuana legalization" and "crime", you seem to be more concerned with use in general and driving, which is a related, but different topic.

Second, the focus of our paper was on crime rates, as opposed to accidents. Crimes and accidents are completely different behaviors--there's this legal concept called "mens rea" the commenter seems to be ignoring. And we know of NO evidence that pot legalization has led to increased car fatalities involving marijuana users with prescriptions. We would argue that for most prescription marijuana smokers who routinely drive under the influence, the laws do nothing more than legalize behavior they were preciously engaged in illegally. In order for this commenter’s theory to be valid one would have to believe that:

1) A significant share of marijuana users obtain prescriptions to legalize their previously illegal behavior and as a result are more willing to driving under the influence of pot, and/or

2) There is a significant increase in the number of persons who become first time marijuana users as a result of marijuana legalization and are also willing to drive under the drugs influence.

While both scenarios are entirely plausible, for now they must remain idle speculation. Perhaps future research will show there is a correlation between the laws and fatal car crashes. But as is the case for any piece of legislation, there can be both unintended benefits and consequences.

Furthermore, the study the commenter mentions regarding driving fatalities is clearly a needed work (see Brady and Li, 2014), and the authors of that study should be commended, however, they do not (and cannot) make any causal claims about what’s actually behind the accidents. Rather they find an increase in the prevalence of toxicology detection, which is an important and telling finding. From that alone, we cannot know whether the cause of the fatality was due to the marijuana use or something else such as more cars on the road in those states, or perhaps in conjunction with substance use, such as icy roads, another driver (perhaps impaired as well), etc.

Marijuana has been shown to impair driving (e.g., Arterberry et al 2013), and the link between alcohol and impairment needs no citation. The real issue should be about per se laws and education to reduce the risk of accidents resulting from marijuana use; just like with alcohol, these tactics can lead to marked reductions in fatalities on the road and should be the focus of your discussion in my opinion (e.g. see Giesbrecht & Greenfield, 2003).

Again, there is no downplaying the importance of educating the public about the hazards of impaired driving, but that doesn't change the fact that we found no link between medical marijuana legalization in increases in state crime rates.

References:

Arterberry, Brooke J.; Treloar, Hayley R.; Smith, Ashley E.; Martens, Matthew P.; Pedersen, Sarah L.; McCarthy, Denis M. "Marijuana Use, Driving, and Related Cognitions" Dec 31 , 2012, doi: 10.1037/a0030877

Giesbrecht, N., & Greenfield, T. K. ( 2003). Preventing alcohol-related problems in the US through policy: Media campaigns, regulatory approaches and environmental interventions. The Journal of Primary Prevention, 24, 63– 104. Retrieved from: http://www.springerlink.c... doi: 10.1023/A:1025027701426