Posted by & filed under Noah's Notes.

I was alarmed in February when I read reports of a study performed by the Governors Highway Safety Association (a national group) which showed that while pedestrian fatalities decreased by 6% in the first 6 months of 2017 compared to the first 6 months of 2016, in the 7 states with legalized recreational marijuana pedestrian fatalities were up more than 16% in the same time period.

Of course, association does not mean causality, but with the inevitability of legalized recreational marijuana and its growing use for a wide range of health issues. I thought it important to understand more about how marijuana can impact driver performance. Fortunately the April 17 edition of JAMA included a piece entitled “Driving Under the Influence of Marijuana: An Increasing Public Health Concern” by Johannes Ramaekers, PhD, who is a at Maastricht University in the Netherlands where they have longer experience with legalized marijuana. In that piece Dr. Ramaekers summarizes what we know about the impact of marijuana on driving:

  • Cannabis is the most frequently detected illicit drug among drivers involved in car crashes and it is often in combination with alcohol.
  • Studies have shown that cannabis impairs driving performance and increases crash risk.
  • Impairment is most significant in the first hour after smoking or consumption and then declines over the next 2 to 4 hours.
  • The impact is equivalent to a blood alcohol level of 0.05 g/dl (legal limits in Maine are 0.08 for adults over 21).
  • Cannabis produces dose related impairments of distance keeping and reaction time (similar to alcohol) and the affect is additive when it is combined with alcohol.
  • Driving impairment occurs in regular users of cannabis as well as those who use infrequently.
  • Cannabis use is associated with a 1.2 to 2 fold increase in crash risk and combining it with alcohol creates a greater risk than the use of either substance alone.
  • Driving under the influence of cannabis was estimated to be responsible for 8700 traffic deaths worldwide in 2013. As a comparison, alcohol accounted for 188,000 such deaths.
  • Regular users of cannabis often admit to driving under its influence and believe that cannabis does not affect their driving, or that they can compensate for it (studies have shown that they cannot).

None of this is to say that we ought to fight legalization (which seems inevitable). Many people, including me, have concerns about the broad application of cannabis for myriad unrelated medical conditions with scant evidence to support its use, but that cat is out of the baggie and it may take decades to gather the real science needed to guide rational decision making. However, the public health impact of the broader availability of marijuana in our state ought to be considered as we develop education programs for users of marijuana and for the public at large. Think of the impact that Mothers Against Drunk Driving has had on our perceptions of that practice. The risks of driving under the influence of marijuana are not as severe, but they are real and they can be reduced by thoughtful consideration of evidence, education and public awareness.

Noah Nesin, MD

Dr. Nesin, Vice President of Medical Affairs for PCHC, is a family doctor with 30 years of experience.

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