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No Direct Correlation Between Driving Impairment And THC Concentration


Leading NIDA researcher Marilyn Huestis admits that there is “no direct correlation between driving impairment and THC concentration” and that “cannabis tolerance may develop in frequent smokers, with less impairment than for occasional smokers with similar THC concentrations.”


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Johnny Green


  1. Even a super high limit has its problems. It’s a problem of proof because no matter how how they got, they’re still back on the ground by the time the blood is drawn.

  2. nygratefulfred on

    If they(gov’t agency,whoever)want to set up a track with real life situations and document reaction times,concentration,etc etc of heavy to light smokers driving under the influence of THC(smoke a Joint before driving the course) compared to totaly sober drivers on the same course,etc then we might find out some truth.

  3. I have known alcoholics that function like normal people and even drive to work over the legal limit on a daily basis without even a traffic ticket. There will always be exceptions to the rule and it is up to the police officer to determine if the driver is impaired, initially.

    I watch as somewhat intelligent people say and do unintelligent things when it comes to cannabis and impairment. But, we have seen actual demonstrations by BBC and CNN regarding cannabis and motor vehicle use and impairment totally discredit the 5 nanogram DUI limit.

    When I was younger my stoner friends would use cannabis on all of our road trips to the great outdoors without any complications (I do not advocate any drug use while operating a motor vehicle), so I have real life experience concerning DUI of cannabis. We need to establish a safe standard that is also backed by unrestricted and unbiased scientific research in order for law enforcement to operate effectively and that will come in time.

    All of this will be settled by the insurance companies as they attempt to insure drivers and remain profitable. Insurance companies are on both sides of the issue, insuring cannabis users and non cannabis users. They can be adversely effected by THC limits that are too low as they pay out for claims that are regulated by ambiguous laws.

    It is the federal government’s fault that we know very little about cannabis and DUI. The federal government would not allow any research that could be interpreted to support the benign nature of cannabis. Run the experiment (trails), collect the data, do the math, amend the laws then shut up…

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