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


thc marijuana cannabis skin allergiesBy Paul Armentano, NORML Deputy Director

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 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.

Source: NORML - make a donation


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Johnny Green


  1. Right pencil neck, last time I driven stone was @14 years ago to avoid the very possibility of jail time so no satisfaction for you.

  2. Brilliant, be sure to give that a try and let us know how it worked out for you after being released from jail.

  3. Good study. If most people vaped, ate, or smoked weed before driving the result would be less wrecks and fender benders because no one would be driving with their ass on fire to get somewhere.

  4. Jordan Shorette on

    it is kind of crazy to think how much progress has been made even in the last few years. I wish we could stage a protest in the capital, Im talking hundreds of thousands of supporters show up and tear their doors down. I mean what choice would they have if that many people show up on the white house lawn, sure as hell cant sandbag them all.

  5. Don’t forget to mention the NHTSA study done in 1993. http://ntl.bts.gov/lib/25000/25800/25867/DOT-HS-808-078.pdf

    “This program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to the consumed THC dose. The impairment manifests itself mainly in the ability to maintain a steady lateral position on the road, but its magnitude is not exceptional in comparison with changes produced by many medicinal drugs and alcohol. Drivers under the influence of marijuana retain insight in their performance and will compensate where they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.”

    “It is possible to safely study the effects of marijuana on driving on highways or city streets in the presence of other traffic.”

  6. I don’t think they will ignore it, since they will no doubt be hammered over the head with it by anti-prohibitionists. Instead I predict they will try, in some way, to come up with their own study or will attempt to poke holes in this one. Either way, their world is shrinking around them. All the “more studies” they call for are coming down against them.

  7. Jordan Shorette on

    just another study that the prohibitionists will ignore, 1000 dollars says in a month they will still be whining our roadways our roadways those stoners are killing us all!

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