Federal Study: THC-Positive Drivers Not More Likely To Be Involved In Motor Vehicle Crashes

Drivers who test positive for the presence of THC in blood are no more likely to be involved in motor vehicle crashes than are drug-free drivers, according to a federally sponsored case-control study involving some 9,000 participants. The study, published Friday by the United States National Highway Traffic Safety Administration (NHTSA), is the first large-scale case-control study ever conducted in the United States to assess the crash risk associated with both drugs and alcohol use by drivers.

Authors reported that drivers who tested positive for any amount of THC possessed an unadjusted, elevated risk of accident of 25 percent (Odds Ratio=1.25) compared to controls (drivers who tested negative for any drug or alcohol). However, this elevated risk became insignificant (OR=1.05) after investigators adjusted for demographic variables, such as the drivers’ age and gender. After researchers controlled for both demographic variables and the presence of alcohol, THC-positive drivers’ elevated risk of accident was zero (OR=1).

By contrast, researchers reported that drivers who tested positive for low levels of alcohol possessed a statistically significant risk of accident, even after controlling for demographic variables (e.g., Drivers with a BAC of 0.03 possessed a 20 percent greater risk of motor vehicle accident [OR=1.20] compared to controls). Drivers with BAC levels of 0.05 possessed a greater than two-fold risk of accident (OR=2.07) while motorists with BAC levels of 0.08 possessed a nearly four-fold risk of accident (OR=3.93).

Researchers did not analyze drivers’ THC levels to similarly estimate whether higher or lower THC levels may impact crash risk in a dose-dependent manner, as has been previously reported in some separate analyses of fatal crash data.

Authors concluded, “This finding indicates that these other variables (age, gender, ethnicity, and alcohol use) were highly correlated with drug use and account for much of the increased (crash) risk associated with the use of illegal drugs and THC.”

The study’s finding contradict allegations by NIDA and others that “marijuana use more than doubles a driver’s risk of being in an accident,” but are largely consistent with those of a 2013 literature review published in the journal Accident Analysis and Prevention which reported that cannabis-positive drivers did not possess a statistically significant risk of a either fatal accident or a motor vehicle accident causing injury.

See NORML’s white paper on cannabis and psychomotor performance here.

19 thoughts

  1. I am glad you posted this as the Colorado Marijuana Authority report was just released to the public. The accompanying article is something for the opposition to run with like there is no tomorrow!!!
    As a published author, I am writing a rebuttal to the study the Colorado Authority admits uses research from illegal times, from NIDA, and assumptions of auto injury when they have no idea of other drug involvement especially fatigue or alcohol.
    My wife is a DHS Administrator who could gather far better data if a quick visit were required. Then they could have accurate, 100% verified, and reliable data rather than the 3,974 that returned survey’s. I do not know Colorado’s exact population, but I know at least that lived in my immediate area when I lived in SE Denver.
    As other states will be using this model, let’s get my cannabis supporting wife involved and kick federal public health workers out of their program, as they stated this administration was responsible for a great deal of the information they were forced into publishing. If they are going to allow the publication of despotic dis-information, I think Colorado should spend some of that tax money into people who could give them 100% accuracy, as part of a team that will make real contacts with 100% of consumers and be an advocate they can call without fear of reprisals. Something they should have had from day one with the Nation looking toward them for a future for cannabis!!!

  2. Why do we need “science” to show us what our eyes already are telling us? Marijuana’ed drivers are not more dangerous. Just fucking stop with the non-logical comparisons to alcohol already!!!!!!!! The only fucking connection, which again you can see with you own eyes, is people at parties like to drink alcoholic beverages and smoke weed. People crash their cars after partying because they drank alcohol which shuts down you nervous system. The marijuana does not shut down the nervous system and it cannot contribute to crashes. Modifying you consiousness is not the same thing as turning it off. Marijuana slightly modifies while alcohol turns off. These are two completely different effects.

    It is all just a stupid association with drunks crashing their cars and sometimes those drunks also smoked weed. It has nothing to do with the marijuana!!!!!!! It is not able to produce effects on a human counter to its own chemistry!!!!!

    At this point, it isn’t just an “association” it is an “over association”. Fiction as fact.

  3. While I am a bit skeptical, and find stoned driving a very terrifying experience, I’ve never been in an accident while stoned either.

  4. “marijuana use more than doubles a driver’s risk of being in an accident,” according to the prohibitionist organization known as NIDA.

    First, I have never believed this BS!

    Secondly, even if it is true, then if my risk of being in an accident is doubled or even quadrupled it is not a reason to be concerned if your risk is close to zero to begin with! Basic math shows us that zero times anything is zero.

    Third, my practical experience tells me that driving under the influence of cannabis is completely safe as long as you’re a good driver to begin with. I’ve driven under the influence of cannabis more than a thousand times and have a perfectly clean driving record!!! Well, except for one minor fender bender. I hit someone from behind after they suddenly slammed on their brakes. The interesting thing is, I was completely straight when it happened. That was about 20 years ago and no one was hurt.

  5. I keep saying this but:
    1) back “in the day” I had a car for 13 years that I put almost 300,000 miles on, and a huge percentage of that was stoned. Not one accident until I was driving in downtown Columbus and another car changed lanes and pushed me out of my lane, up on the sidewalk. I narrowly missed a bus stop with people in it.

    can’t remember if I was high in that incident (though I definitely had metabolites in my system) but on three other occasions when I WAS driving stoned, I missed a head-on crash when an oncoming driver swerved into MY lane and it was ME that avoided an accident. ONe car had actually lost control and bounced across the grass median into my lane, another was coming around a blind curve, and the other was because it was icy and that car swerved to avoid the car in front of it that had braked. bad drivers abound but I’m not one of them.

  6. @shawn kearney:
    February 10, 2015 at 2:25 am
    – –

    the fact that you find stoned driving
    a “terrifying experience”,
    (I’m also apprehensive to drive when high),
    demonstrates that the cannabis high ITSELF
    is its own DUI deterrent, (UNLIKE alcohol).
    “I don’t want to drive anywhere, I feel too baked!!!”
    vs. alcohol:
    “I’m okay to drive, I’ve only had a few drinks!”].

  7. People on THC are aware of their impairment and compensate for it. People on ethyl alcohol endanger us all.

    Bars with parking lots – think about it.
    Marijuana ‘coffeeshops’ appear to be a much safer alternative.

  8. People, this article refers to THC in the system, not driving stoned, I believe.

    I personally think we shouldn’t drive stoned, period, simply out of respect for others’ fears. Because the more we can demonstrate that cannabis consumers ARE responsible adults who respect their fellow citizens and use cannabis safely in whatever capacity they choose (be it medicinal or recreational), the better it is for the cause.

    Personal experience or ability to drive stoned aside, this small concession will go a long way towards assuaging the fears of those who don’t have a strong opinion on legalization one way or the other. Don’t be the prohibitionists’ ‘example’ of why pot is ‘bad’. Prove them wrong, instead. It’s much more gratifying.

    That’s just my 2 cents. Have an awesome day everyone!

  9. Awww Maaaan! Now how are law enforcement suppose to artificially line city budgets? I know!; Meth outbreak! Zombie Apocalypse! (Lol) What will they think of next? Prohibitionists are running out of false justifications for unconstitutional enforcement of marijuana policy faster than the DEA can raid the wrong house. It appears as though the ONDCP is no longer in tight control of our domestic federal research of marijuana anymore.

  10. Well I have road with both drunk & someone stoned. Would feel a hell alot safer with the stoner. It would be a lot more comical. Instead of the drunk that wants to fight, steal something.

  11. @Drummer Man – I completely agree with you that people should not drive stoned. Prohibitionists, or those among us that simply choose not to use cannabis, need to understand that we don’t get “stoned” every time we consume. Just as people can have a drink or two of an alcoholic beverage without getting drunk, people can consume a small amount of marijuana without getting stoned! Even if someone does get stoned, it only takes a couple of hours before they are perfectly capable again (of doing anything they need to do).

  12. I don’t drive stoned. Never have, never will because getting stoned involves closing your eyes…can’t drive and do that. But I will drive when I medicate, just not right after consuming. It is not right that someone medicating with cannabis has to give up their rights to drive simply because the definition of impairment is clouded in political and cultural descriminations and not science.

  13. Cannabis is non-toxic and does not cause impairment.

    If anyone can cite credible evidence proving cannabis use impairs driving skills ,please do so?

    [Editor’s note: OK…you’re on a pro-cannabis webpage claiming that cannabis does not cause impairment. Really? If this is true, then the editor and everyone they know who uses cannabis must be doing something wrong or must not be consuming actual cannabis products. Why would humans consume cannabis for thousands of years? The taste of the smoke? There are over a hundred films based on cannabis’ legendary effects (from Cheech-n-Chong to Fast Times at Ridgemont High to Harold & Kumar, etc…) and creating laughs at the self deprecation of the obvious: cannabis causes impairment

    Of course cannabis is a psychoactive drug that causes impairment in humans. Isn’t that largely the point? It’s mild, pleasant and short-lived impairment is why it is arguably one of the most popular drugs in human history.

    Even experienced cannabis users, notably after consuming cannabis edibles or inhaling the vapors of potent cannabis oils and concentrates are ill advised to operate heavy machinery, autos, planes, etc…for at least seventy five minutes after inhaling cannabis products; potentially a few hours after cannabis has been ingested.

    The charts via National Institute of Health are fairly clear regarding the immediate uptake of cannabis into the body upon inhalation, and how reasonably quickly it dissipates the body. It is the immediate uptake of cannabis that is both desired by medical patients (and consumers as well) and vexing for public safety from law enforcement’s point of view.

    Changes in performance are typically dose-related. Changes in performance are most acute in naïve users. Changes in performance are typically short-lived:

    –70 percent of subjects manifest ‘significant’ psychomotor impairment 20-40 minutes following cannabis inhalation; this percentage falls to 30 percent after 60 minutes (Berghaus et al., 1998 as cited by Gieringer)

    –Peak acute effects following cannabis inhalation are typically obtained within 10 to 30 minutes (NHTSA. 2004. Drugs and Human Performance Facts Sheets)

    –“Experimental research on the effects of cannabis … indicat[e] that any effects … dissipate quickly after one hour.” (NHTSA. 2003. State of Knowledge of Drug-Impaired Driving: FINAL REPORT)

    –“[T]he cannabis effect (on driving performance) tends to disappear after the first 60 minutes of use.” (Pulido et al., 2011. Cannabis use and traffic injuries.)

    After nearly 45 years of publicly advocating for an end to cannabis prohibition, NORML doesn’t suffer fools in government who want to maintain the status quo on such a failed public policy only to, at the end of cannabis prohibition, broadcast the notion at all that cannabis, a much maligned and misunderstood herbal drug, and most notably it’s produced high potent products (hash, oils, concentrates, edibles), do not cause any impairment in humans.

    NORML is about addressing the government-fostered myths of cannabis, not creating new ones that are not sustained by personal experiences, culture or science.]

  14. in 32 yrs of consuming cannabis, I have never had a problem with driving after an “adjustment”(one or two hits).i have been comfortable and safe, on the other hand, I have been too buzzed to drive and have gladly handed my keys over to a responsible driver. I say that to say this, I would GLADLY never drive again after ANY consumption of cannabis if these laws can be changed to allow me to consume cannabis legally.if that is what it takes I will gladly do it! thank you norml for your hard work to get us this far!now , we as consumers must put forth some effort to help this happen. we must do the right things so we can enjoy the herb!

  15. “NORML is about addressing the government-fostered myths of cannabis, not creating new ones that are not sustained by personal experiences, culture or science.”

    Well I rub elbows with people of all sorts of different cultures. The kids are all convinced that they cannot drive while stoned, which isn’t a bad thing. However, I know people that can roll blunts one handed so they can roll up while driving. They smoke huge blunts while driving and suffer no negative driving effects. I’m not saying this behavior should be promoted, but it should not be punished either…

    Clearly, there is some dichotomy regarding different kinds of marijuana and also the particular person that imbibes them. Which should be recognized in our laws.

  16. The last Editor’s Note doesn’t address the question of how much driver impairment attributed to cannabis is caused by the “marijuana $igarette” or 500-mg Joint which contributes avoidable carbon monoxide, heat shock and Combustion Toxins when VAPORIZATION is available and can even be performed successfully with a $1.29 handmade single toke utensil (25 mg per serving).

    Probably no. 1 reason for popularity of the big fat Joint is that it is easiest to hide, and evidence of use most quickly disposed of. Prohibition drives anxious naïve users to use up that $$ large amount quickly under the ignorant assumption that little ingredient benefit is thereby burned/wasted and in hasty defiance of whatever warnings of impairment.

  17. What if alcohol use could be detected for days and weeks after consumption?

    Would anyone seriously suggest a DUI in those cases.

    No!…case closed?

    “Common sense ain’t that common” – Lefty Kreh

  18. Keep up the good work,me personally I suffer from bipolar disease sleeping disorders and some. I think its the greatest medicine ever with no deaths. Cancer fighting calms people down and all of the above. I’m in Louisiana and its hard to get it across to people. I’ve been an advocate for a long time. Made mistakes but it don’t mean we don’t need this medicine here in Louisiana. If you can help us down here it would be greatly appreciated. Everyone in the world needs it especially us. Thanks and keep fighting.

  19. I believe the first thing that really needs to be done is to develop a test for CURRENT MARIJUANA INTOXICATION, not simply a test for RESIDUAL MARIJUANA METABOLITES, which do not justify a basis for intoxication. This is because marijuana metabolites detected in a standard urinalysis are stored in fat cells and can remain in the system for a month or more. Anyone, even our lawmakers who have tried marijuana and DID inhale, can agree that they would no longer be high a month after smoking a joint, or even six hours after doing so. Our scientific community is lagging, and is keeping us down. This in terms of false DUI arrests, as well as employer drug screenings.

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