Driving High
High Times April 2018
2015 the AAA Foundation will likely follow a similar for Traffic Safety commistack. “As more and more sioned a study to determine voters are showing their whether there was any tolerance for state-legal correlation between blood marijuana, legislators aren’t concentrations of THC and necessarily going to be up to driver impairment and speed on the issue and are crash risk. The study results going to copy what states were decisive, says lead like Colorado and Washingauthor Barry Logan, chief of ton have done,” says Skyler forensic toxicology at PennMcKinley, director of public sylvania-based NMS Labs relations and government and a leading figure in drugaffairs at AAA Colorado. impaired-driving research. “They are going to get these “Our conclusion was you laws on the books as part are not going to find a blood of these big packages of concentration level for canlegislation.” nabis that is a useful tool for That means a growing deciding whether someone number of states will likely is under the influence or end up with nice, tidy rules not,” says Logan. “You can’t on which to base cannabisreally say anything based on and-driving cases. There’s the number.” only one problem: ScientifiThanks to findings like cally, everyone agrees these that, both the American rules don’t make much Automobile Association and sense. the National Safety Council For starters, unlike these now recommend against new cannabis traffic-safety states basing cannabis and laws, blood-alcohol limits driving laws on cannabisfor driving weren’t hashed blood-concentration levels. out over legislative bargainEven the National Highway ing tables. They were careTraffic and Safety Adminisfully determined through tration has conceded in past extensive and meticulous reports that “It is difficult car-crash studies in the to establish a relationship late 1960s overseen by the A GROWING NUMBER OF STATES WILL LIKELY between a person’s THC country’s first traffic czar, END UP WITH NICE, TIDY RULES ON WHICH blood or plasma concenWilliam Haddon Jr., a TO BASE CANNABIS-AND-DRIVING CASES. tration and performance trained epidemiologist. The THERE’S ONLY ONE PROBLEM: SCIENTIFICALLY, impairing effects.” result was a pioneering set EVERYONE AGREES THESE RULES DON’T It’s possible, however, of laws based on science, that researchers will eventunot politics. MAKE MUCH SENSE. ally find a reliable way to Alcohol was uniquely draw a parallel between impairment a breathalyzer for any of the hundreds suitable to regulations and tests based and evidence of cannabis in the body. of other things that can impair your on biological indicators, such as bloodVandrey, for example, is working on a driving.” alcohol concentrations and alcohol levels new study that will scrutinize a variety of Cannabis impairment, on the other on a subject’s breath. That’s because biological markers to see if any correlate hand, doesn’t seem to track consistently unlike the vast majority of drugs, the consistently with impairment. But even with THC levels in a subject’s system relationship between alcohol levels in if scientists do hit upon a way to gauge at all. Intoxicating effects can vary the body and alcohol intoxication remain cannabis intoxication through something widely depending on the method of markedly constant from one person to like a blood test, there’s another problem. consumption, and longtime marijuana the next. “THC drops precipitously after someusers tend to build up a tolerance to its “Alcohol is conveniently emitted body stops using cannabis,” says Logan. performance-impairing effects. In other through your breath in amounts that “THC levels fall by about half in 20 correctly predict intoxication and impair- words, it’s possible that a first-time canminutes, and in about an hour it’s about nabis user could be in no shape to drive ment. That is not the case with most 20 percent of what it was originally. So with less than five nanograms of THC drugs,” says Ryan Vandrey, an associate per milliliter of his blood, while a regular in the real world, by the time someone professor at Johns Hopkins University is pulled over, given a roadside sobriety cannabis consumer could have far more School of Medicine who studies the test, then brought to a hospital and had than that level long after all the intoxibehavioral pharmacology of cannabis. blood drawn, that number won’t tell you cating effects of her last smoke session “People often say, ‘We have a breathaanything about the number they had have worn off. lyzer for alcohol, why don’t we have when they were driving.” To get to the bottom of the matter, in one for cannabis?’ Well, we don’t have
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