Driving While Stoned

The New York Times reported earlier this week that driving under the influence of marijuana is significantly less risky than driving with a blood-alcohol concentration of 0.08.  That’s a good thing, since the Times also reported that impairment from marijuana is difficult to detect using the current battery of standardized field sobriety tests and difficult to confirm through subsequent laboratory tests.  The article summarized several recent studies making these findings and noted the conclusion of some experts that public resources would be better spent combating alcohol-impaired driving, including perhaps lowering the per se threshold for alcohol concentrations to 0.05,  than in establishing a per se limit for blood-THC content or devising roadside tests to detect for marijuana impairment.

Why is driving while stoned less risky? The simple answer is that marijuana and alcohol have different physiology. Drivers impaired by alcohol tend to overestimate their skills and drive faster.  Drivers impaired by marijuana do the opposite. A professor of public policy interviewed for the Times article noted the old joke about “‘Cheech and Chong being arrested for doing 20 on the freeway.’”  (The Times ran a picture of the famous comedic duo to accompany its story, which, if you ask me, it should have saved for Throwback Thursday (#tbt)). Studies estimate that drivers who are stoned are twice as likely to crash.  A 20-year-old driver who has a blood-alcohol concentration of 0.08 percent, in contrast, is almost 20 times more likely to be in a fatal accident than a sober driver.

Why is marijuana impairment hard to detect? THC is the chemical that gives marijuana its psychoactive punch. It can take as long as four hours for THC metabolites to appear in urine after smoking, and urine can test positive for those metabolites days or weeks after a person last smoked.  As the National Highway Transportation Administration’s fact sheet on marijuana puts it, this is “well past the window of intoxication and impairment.” And because concentrations of THC in a person’s blood depend in part upon the pattern of marijuana use, it is difficult to establish a relationship between a specified blood concentration and performance impairing effects.  The Times reports that regular marijuana smokers could have a blood-THC content that meets the limits set in Colorado and Washington for THC concentration a full day after they last smoked.

Driving while stoned is illegal in North Carolina as is driving under the influence of any “impairing substance.” Yet, given the scientific limitations discussed above, stoned driving can be a tough case for the State to prove. While the State may establish per se impairment by proving that a person had any amount of a Schedule I controlled substance in his or her blood or urine, to prove impairment from marijuana, a Schedule VI controlled substance, the State must prove that the person’s physical or mental faculties were appreciably impaired by that substance at the time he or she drove.

Governor Pat McCrory recently appointed members to a Statewide Impaired Driving Task Force that is charged with developing a statewide plan for preventing and reducing impaired driving. Should the prevention of stoned driving be a priority for this group?  Or should it instead focus on alcohol-impaired driving?  What should its strategy be?  Adoption or amendment of per se limits?  Expanding options for treatment?  Something else?

Have your say.  Send in a comment below.

8 thoughts on “Driving While Stoned”

    • David: Why drag John Fogerty into this discussion? Seriously, dude…if you can refute what I believe have at it, but implying I am a stoner ( incorrect by the way ) is not conducive to enlightening the masses…have a great day bro!!

  1. Due to the moronic drug war mentality police adopt, ANY use of any substance , other than alcohol, which has a lower limit for presumed intoxication, is assumed to be impairing, despite the facts. While no one should drive when not in control of their faculties , the presence or THC in the system is not a reliable indicator of impairment. Since most drivers who have consumed a moderate amount of pot can easily pass the standard roadside sobriety tests, drivers should not be charged with impairment based only on the smell of recently smoked pot in the car or even the admission that a driver had smoked while driving.

    The allegation that ” ..drivers who are ‘ stoned ‘ are twice as likely to crash, is based on what level of consumption? Who validated the ” studies “? Studies paid for by prohibitionist interests usually use the most extreme examples to try and support their allegations of problem use: Remember the ” scientists ” that mad3e monkeys inhale vast amounts of pot smoke for prolonged periods and then decalred that pot use had the effects seen in the ridiculously overdosed chimps? While no human being in the history of mankind has ever died or had an overdose requiring medical intervention due to pot, we still are subjected to the shrill blatherings of the prohibitionist fear mongers, most of whom have a financial interest in continued lunacy. All one has to do to realize the corrupt basis for anti-pot laws is to read the history, sordid and shameful, of how in 1937 the laws against pot were achieved by the corporate and political charlatans of the period for their own selfish gain.

    Until impairment and not simple use is the standard more injutices will occur. All use is not abuse, and the presence of THc in the system is not a relibale indicator of impairment.

  2. One more item: Virtually all ” treatment ‘ programs for pot use are court mandated and not because someone has a dire need for intervention. The ” rehab ‘ industry of course wants to pretend that casual smokers who get caught with pot need their expensive services, even though cannabis is NOT physically addictive and is no more psychologically addictive than chocolate. gambling, etc. Special interests should not have a say in the upcoming panels seeking limits or standards, and per se rules are bogus insofar as an indicator of impairment is concerned. If a driver is able to demonstrate the acutity needed to pass a roadside impairment test, they should not be charged at all…morally, pot should not be illegal. When a law has no justifiable foundation and is proven to be based on lies, sanctions debase the justice system and bring disrepute to all who enforce the bad laws.

  3. From the linked NY Times article:

    “Still, it is clear that marijuana use causes deficits that affect driving ability, Dr. Huestis said. She noted that several researchers, working independently of one another, have come up with the same estimate: a twofold increase in the risk of an accident if there is any measurable amount of THC in the bloodstream.

    The estimate is based on review papers that considered the results of many individual studies. The results were often contradictory — some of the papers showed no increase in risk, or even a decrease — but the twofold estimate is widely accepted. ”

    Why is it accepted if the results are contradictory? Also:

    “The study’s lead author, Eduardo Romano, a senior research scientist at the Pacific Institute for Research and Evaluation, said that once he adjusted for demographics and the presence of alcohol, marijuana did not statistically increase the risk of a crash.

    “Despite our results, I still think that marijuana contributes to crash risk,” he said, “only that its contribution is not as important as it was expected.”

    So, despite the results, let us assume the worst, even without evidence. They expected one result and got another, so naturally they cling to the presumptions and not the science.
    Typical for studies funded by proponents of the status quo.

  4. My father was killed by a driver with THC in his system. Yet, they will probably be no criminal charges filed. I have smoked plenty of weed and I know that it does impair your ability to drive a car. Folks need to step it up in testing for this and provide justice to families like ours.

    • I’m very sorry to hear about your dad.
      That fact that you “have smoked plenty of weed and (you) know that it does impair your ability to drive a car” is what scientists call anecdotal evidence, and it doesn’t prove anything other than the fact that your driving ability might be impaired.


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