If Medical Marijuana Laws Cause a 'Surge in Drugged Driving Deaths,' Why Are Fatalities Falling?


A study published by the American Journal of Epidemiology last month found that 12.2 percent of drivers killed by car crashes in six states tested positive for cannabinol, a marijuana metabolite, in 2010, up from 4.2 percent in 1999. Here is how NBC News translated that finding in the headline over a story posted on Saturday: "Pot Fuels Surge in Drugged Driving Deaths." The article, which begins by describing the deaths of a Colorado woman and her infant son in a crash caused by "a driver who admitted he smoked pot that day," links the purported surge in marijuana-related traffic fatalities to laws allowing medical use of cannabis. "As medical marijuana sales expanded into 20 states," writes health reporter Bill Briggs, "legal weed was detected in the bodies of dead drivers three times more often during 2010 when compared to those who died behind the wheel in 1999." There are several problems with reading the trend described by this study as evidence that legalizing medical marijuana causes an increase in fatal car crashes:

1. The fact that cannabinol was detected in a driver's blood does not mean he was under the influence at the time of the crash, let alone that marijuana caused the crash. "It is possible for a driver to test positive for cannabinol in the blood up to 1 week after use," the researchers note. "Thus, the prevalence of nonalcohol drugs reported in this study should be interpreted as an indicator of drug use, not necessarily a measurement of drug impairment."

2. Only three of the six states included in the study (which were chosen because they routinely do drug testing on drivers killed in crashes) have medical marijuana laws: California, Hawaii, and Rhode Island. 

3. Traffic fatalities fell by more than 20 percent nationwide during the study period, even as "medical marijuana sales expanded." Between enactment of its medical marijuana law in 1996 and 2010, California saw a 31 percent drop in traffic fatalities. The number of traffic fatalities also fell in Hawaii and Rhode Island after they legalized medical marijuana—by 14 percent and 21 percent, respectively.

4.  A study published last year by the Journal of Law & Economics found that adoption of medical marijuana laws is associated with a decline in traffic fatalities, possibly because people in those states are substituting marijuana for alcohol, which has a more dramatic impact on driving ability. Briggs mentions that study in the 17th paragraph of his article.

It is important to keep these points in mind as more states liberalize their marijuana laws, especially since "preventing drugged driving" is one of the "enforcement priorities" that the Justice Department says might justify federal interference with legalization in Colorado and Washington. If "drugged driving" means operating a motor vehicle with any detectable amount of cannabinol in your blood, "drugged driving" inevitably will rise after legalization as consumption rises. But having cannabinol in your blood is not the same as being intoxicated. And even if the share or absolute number of traffic fatalities caused by marijuana-related impairment rises, the total number of traffic fatalities could still drop thanks to substitution effects. Regardless of what happens with traffic fatalities, the possibility of marijuana-related accidents is a reason for discouraging people from driving while impaired, not a reason for prohibiting the drug altogether. 

NEXT: Project SAM's Patrick Kennedy: "Treatment or Jail" for Pot Users

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  1. Many years ago I was on a bicycle and some fifteen year old kid hit me in a crosswalk after running a red light.

    Because I’d had a couple drinks, the cop gave me a DUI and let the kid go.

    So an accident resulting from a fifteen year old kid running of a red light was chalked up to alcohol.

    Remember that the next time something is described as alcohol or drug related.

    1. Teenagers are manic for alcohol. Clearly the fifteen year old sensed it in your blood and drove through the red light to get to it.

    2. I had a similar incident happen to me. A guy backed into me in the parking lot of the PX when I was in the Marine Corps. I had been out the night before and I guess the MP smelled a little alcohol on my breath. So, they take me down to the station and do a sobriety test, and a breath test on their best breathalyzer (I blew a .01). Anyway, I passed both with flying colors. So, they said sorry for the trouble. You are free to go. I didn’t think anything about until I had to get a copy of the accident report for my insurance company. At which point I found out that, even thought alcohol had nothing to do with the accident. It was still labeled an alcohol involved accident.

      1. This is a pattern one can see wherever officious busybodies are trying to demonize something. Many people, Mr. Sullum among them, have pointed out that in the absence of objections from family, pretty much any death in the U.S. caused by those illnesses that “have been determined” to be associated with smoking are likely to be recorded as smoking related deaths, whether the deceased was ever exposed to tobacco smoke or not.

        I sometimes wonder just how much of this unmitigated hogwash influences all Public Heath policy, and if anything can be done about it.

        1. I guess if you still don’t have the results you where hoping for after cherry picking data, you might was well skew the data set too.

  2. So if you are a stoner quietly driving along one night and a drunk driver comes over into your lane, hits you and kills you, you will be counted as having died from pot (or it will be considered a contributing factor) because of the metabolites in your system, yes?

    1. Not only will you be counted as having died from pot, but the drunk’s lawyer just might be able to use it in the guy’s defense.

      1. Ugh, unfortunately you’re not using sarc.

        1. He’s probably right and the drunk driver could argue you were stoned and pot is higher up on the scale of “evil substances” so they’d rather label it a pot-caused crash and let the drunk off.

          I don’t understand why people want to eff themselves up so much. If your life sucks so much you need depressants/stimulants to feel better (for a brief time) there are underlying problems you’re just sweeping under the rug. Really the law is the least of your problems.

          1. That said legalization still has merits mainly because it will end the drug pushers on the streets, bring down prices (which lowers the percentage of the economy wasted on drugs), and allow some pot smokers to at least keep their low-level jobs (like a guy in retail I knew was to be fired even though the company wanted to keep him, because of drug testing). Plus once a person is labelled a felon they can never get a job again basically and are forced into a life of crime. Which is a complete shame in the case of non-violent drug users who should be in therapy not prison.

  3. “Alt-text’s not here, man.”


  4. Expect the jackboots and drug warriors to fight legalization tooth and nail. Anything that is not an expansion of the police state will always inspire hysteria in these types. Fortunately they are going to lose this one, but brace yourself for every lie, deception and desperate tactic they can conjure up.

    I am shocked that NBC news would be going along with the statist control freaks on this. Shocked I tell you.

  5. No PM links?

    This is the first day for some time that I was not going to miss them. Geez.

    1. It’s President’s Day, so no PM Links. Go do something Presidential instead, like pardon a turkey or drone someone. If you’ve offended anyone lately, apologize for not getting the messaging right.

  6. I get home from a long day at the office and this is the best Reason can do for today?

    I’ll bet we won’t even get a proper Independents thread! Although at least this one isn’t about child porn.

  7. Everybody go & get into a crash while sober to drive down the stats!

  8. NPR interviews Caro the LBJ biographer. His latest volume covers 1958 to 1964.

  9. Don’t bother Nazis with the truth. It’s a mindset: set on telling others what to do.

  10. Sullum, your argument is measured, logical, and even-handed. In other words, it’s bound to be rejected by The American People.

    Most of the population, especially Soccer Moms, are easily whipped into a frenzied panic.

    In other words, we’re fucked.

    This–this I tell you–is how they will arrest the progress of cannabis legalization. One one cherubic toddler will tragically lose her life to a car crash where one driver has trace CBD in their system and we’ll be back to life sentences for a single roach.

    The wisdom of the everyday American can never be underestimated. We are so fucked. What kind of cowardice has prevented me from suiciding already?

    1. Thus conscience does make cowards of us all;
      And thus the native hue of resolution
      Is sicklied o’er with the pale cast of thought,
      And enterprises of great pith and moment
      With this regard their currents turn awry,
      And lose the name of action.

    2. The *cowardice of the everyday American can never be underestimated.


  11. “A study published this year…”

    Nice attempt to change the subject, but I’m on to you. We’re supposed to be talking about the evils of the killer weed, and you’re talking about some *study*? Don’t you care about the children?

  12. “A study published this year…”

    Nice attempt to change the subject, but I’m on to you. We’re supposed to be talking about the evils of the killer weed, and you’re talking about some *study*? Don’t you care about the children?

  13. Sometimes man you jsut have to roll that beautiful bean footage!

  14. Why does most everyone automatically jump to the automatic, knee-jerk, and FALSE assumption that cannabis impairs drivers much the same as does alcohol? Why let uninformed opinions be the basis of new laws? It took me very little time to do a search, and find actual scientific studies which indicate just how incorrect such an assumption is. Examples follow.

    Studies Show Marijuana Consumption Not Associated With Dangerous Driving, May Lead to Safer Drivers
    Anyone who consumes cannabis on a regular basis knows that it doesn’t make you a dangerous driver. Many people find that it makes them a safer, more focused driver; one that’s more aware of their surroundings and the dangers associated with controlling tons of gasoline-filled metal. Not only has this been an anecdotal truth for as long as cars and cannabis have been paired, science has also been clear that consuming marijuana doesn’t make you a dangerous driver, and may make some people safer drivers. More research is needed, but it’s hard to deny that of the research we have, marijuana hasn’t been found to increase a person’s risk of an accident. To back this claim up, here’s a list of studies and research conducted on this very topic, some of which were funded by national governments in hopes of different results.…..r-drivers/

  15. Marijuana and Driving: A Review of the Scientific Evidence
    “Marijuana has a measurable yet relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. Below is a summary of some of the existing data.”…..c-evidence

    The incidence and role of drugs in fatally injured drivers
    “There was no indication that cannabis by itself was a cause of fatal crashes.”
    REFERENCE: Washington, DC: US Department of Transportation, National Highway Traffic Safety Administration,
    Report No. DOT HS 808 065, K. Terhune. 1992.…..08_065.pdf

  16. Marijuana and actual driving performance
    “Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.”
    REFERENCE: U.S. Department of Transportation study, 1993…..g/s1p2.htm

    Marijuana’s effects on actual driving performance
    “Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution”
    REFERENCE: University of Adelaide study, 1995

  17. Role of cannabis in motor vehicle crashes
    “There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.. The more cautious behavior of subjects who have received marijuana decreases the impact of the drug on performance, whereas the opposite holds true for alcohol.”
    REFERENCE: Marijuana: On-Road and Driving-Simulator Studies; Epidemiologic Reviews 21: 222-232, A. Smiley. 1999.

  18. I am shocked that NBC news would be going along with the statist control freaks on this. Shocked me

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