Marijuana Law, Policy & Reform

Editor: Douglas A. Berman
Moritz College of Law

Thursday, January 10, 2019

"Driving under the influence of cannabis among medical cannabis patients with chronic pain"

X03768716The title of this post is the title of this notable new study just published in the journal Drug and Alcohol Dependence. Here is its abstract:


Driving under the influence of cannabis (DUIC) is a public health concern among those using medical cannabis.  Understanding behaviors contributing to DUIC can inform prevention efforts. We evaluated three past 6-month DUIC behaviors among medical cannabis users with chronic pain.


Adults (N = 790) seeking medical cannabis certification or recertification for moderate/severe pain were recruited from February 2014 through June 2015 at Michigan medical cannabis clinics.  About half of participants were male (52%) and 81% were White; their Mean age was 45.8 years.  Participants completed survey measures of DUIC (driving within 2 h of use, driving while “a little high,” and driving while “very high”) and background factors (demographics, alcohol use, etc.). Unadjusted and adjusted logistic regressions were used to examine correlates of DUIC.


For the past 6 months, DUIC within 2 h of use was reported by 56.4% of the sample, DUIC while a “little high” was reported by 50.5%, and “very high” was reported by 21.1%. G reater cannabis quantity consumed and binge drinking were generally associated with DUIC behaviors.  Higher pain was associated with lower likelihood of DUIC.  Findings vary somewhat across DUIC measures.


The prevalence of DUIC is concerning, with more research needed on how to best measure DUIC. Prevention messaging for DUIC may be enhanced by addressing alcohol co-consumption.

Medical Marijuana Data and Research | Permalink


Here are a few concerns.

Before I present my concerns, let’s start with some (what I assume are) common goals. No person should be driving impaired. Regardless of the cause of the impairment. No matter whether the cause is the consumption of THC, ethanol, or simply lack of sleep the results of impaired driving can devastating.

Obtaining meaningful information about the effects of marijuana is important to understanding the limitations we should (and shouldn’t) put on drivers who consume marijuana. What does not help achieve these goals is misinformation, flawed methodologies or biased data.

I have a hard time understanding the value of this paper. While the authors are honest about its limitations, they still engaged in a process that did not even seem capable of proving anything scientifically meaningful.

To illustrate:

1. The Chosen Sample - “among medical cannabis users with chronic pain.” Why use only this group? Wouldn’t you also want users without the variable of “chronic pain”? (801/770 people is a good size, but why only this criteria).

2. Relying on Self-Reporting – THC impairs a person’s mental abilities. That is why we care about its use while driving. Accordingly, it doesn’t make much sense to assume, a person’s memory about what happened while impaired would be reliable.

3. Lack of Defined Terms – asking a person about their degree of being “high” is problematic. This is not a standardized term. What we want to know is whether “impairment” occurred while driving. Impairment being - a measurable difference below - a person’s normal baseline driving ability - resulting from the consumption of THC.

It’s a credit to the authors that they acknowledged this paper’s limitations. However, the limitations were obvious before they began. Why not conduct something that is capable of providing the data we want and meets our common goals?

Posted by: Lawrence Koplow | Oct 10, 2019 10:25:33 AM

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