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The Difficulties Of Establishing A Legal THC Driving Limit

By Roger Moleskin photo/istock/Shidlovski

As the legalization movement moves ever closer to success on a national level, there are many aspects to establishing a legal marijuana market into society. The one that will likely affect most users is the establishment of a legal THC limit for driving. Many users will say that driving while high does not affect their ability to drive, and they may be right, but it’s not the case for everyone. It’s a reality and only fair that there be a limit to the amount of THC allowed to drivers just like alcohol, but implementing that limit is much more complicated than one might think.

 The main problem is the fact that THC metabolizes in the blood much differently than alcohol does. Thomas Marcotte, co-director of The Center for Medicinal Cannabis Research at the University of California, San Diego, says that "Unlike alcohol, which has a generally linear relationship between the amount of alcohol you consume, your breath alcohol content and driving performance, the THC route of metabolism is very different.”

He continues; "You can be positive for THC a week after the last time you used cannabis". "Not subjectively impaired at all, not impaired at all by any objective measure, but still positive."

This means that a THC test that mirrors a standard alcohol sobriety test in a useless method in determining if a driver is impaired. Take for example the case of Abby Mclean, from Northglenn, Colorado. She was driving home from a dinner party when she was stopped at a DUI checkpoint. Although she insists she never drives while high, the test administered found her THC levels over 5 times the legal limit.

Each state sets up its own THC limit laws, and in Colorado that limit is 5 nanograms per milliliter of blood. McLean’s lawyer successfully (and rightly) argued that the number does not reflect the state of impairment the same way alcohol does, and Abby got off with a hung jury. However she is just one success story out of hundreds, if not thousands, who do not get off.

 As is stands now, the marijuana drug-impaired driving laws vary wildly from state to state:

 ●      9 states have zero tolerance for THC or a metabolite.

●      3 states have zero tolerance for THC but no restriction on metabolites.

●      5 states have specific per se limits for THC

●      1 state (Colorado) has a reasonable inference law for THC

 So is there a reliable and fair way to implement a roadside sobriety test for marijuana? Scientists at UCSD are working on several methods but they are all still in the experimental phase. Denver District attorney Matt Morrissey knows this and feels the best course of action is to wait until new methods are developed.

 "I think that putting in a nanogram level makes sense," says Morrissey. "I can't tell you what level it should be. I don't think Colorado's is right. I don't think it should be as high as it is. I think it should be lower." "I think that has to do with better testing better technology,"