BY CHRIS POWERS
SC Staff Writer
Intuitively, when one thinks of being impaired by drugs while driving, they think of any kind of drug, marijuana included.
According to a 2012 study, only thirty percent of people under the influence of marijuana who regularly smoked failed a field sobriety test, the primary field test for a DUI.
Fifty percent of marijuana smokers failed if they did not regularly smoke.
This test ordinarily catches over ninety percent of drunk drivers, suggesting that marijuana is less of a factor than alcohol.
Driving under the influence of marijuana, however, is still not as safe as driving sober, and it has been shown by several independent researchers that driving under the influence of THC (the active ingredient in marijuana), increases the chance of an accident by two-fold.
Contrast this with the fact that a 20-year old with a B.A.C. (blood alcohol content) of 0.08 percent had about a twenty-fold increase of having an accident, and marijuana seems relatively safe.
Eduardo Romano, a senior research scientist at the Pacific Institute for Research and Evaluation, stated that marijuana did not statistically increase the crash risk.
That is not to say that it is not a contributing factor, but, as Romano stated, “Its contribution is not as important as expected.”
This is a statistic that is also difficult to measure, due to the fact that THC cannot be measured on the scene of an accident or a traffic stop, but must be taken from blood, urine, or hair samples taken after an arrest.
This is also problematic because, due to the nature of the urine test, which detects an enzyme that breaks down THC, a false positive may be shown, according to David Gieringer, director of NORML, a drug advocacy group, “from four to ten days after a single use.”
In the states where marijuana is legal, 5 ng/L of blood has been set for the legal limit of a blood test.
THC’s tendency to build up in the body and release over time may also cause problems for the detection via blood tests.
According to Gieringer, “there is no clear correlation between THC blood levels and actual impairment.”
It is currently unclear to what extent levels of THC in the blood may impair driving, and there are few ways to conclusively test for impairment. Future studies are on track to introduce a successful way to measure the levels of THC and its correlation to driving.
Email Chris at: