A recent New York Times piece bears the pithy headline: ‘How Much Is Too Much Marijuana to Drive? Lawmakers Wonder’. We wondered too. We took a look at the article, and at the American Automobile Association’s new study, cited by the Times. It’s posted on AAA’s website, along with a lot of other interesting information on this topic. The study’s called ‘An Evaluation of Data from Drivers Arrested for Driving Under the Influence in Relation to Per se Limits for Cannabis’ and its answer (on Page 3 of the report) to the question posed by the Times, “how much is too much?” – that “a quantitative threshold for per se laws for THC following cannabis use cannot be scientifically supported,” – boils down to “it depends.”
Meanwhile, at least three states, according to the study (on Pages 2 and 25) have put per se limits on the amount of THC you can have in your system and drive legally. ‘Per se‘ is latin for ‘in and of itself’. If you adopt a per se rule, you’re saying that any other fact is irrelevant. “I don’t care whether you were impaired or not,” the rule says, “I’m not punishing you for being impaired; I’m punishing you for driving with x amount of a substance in your system!”
The authors of AAA’s study concluded, however, that if the purpose of per se statutes is to deter impaired driving, they don’t do a very good job. Because of the nature of THC (‘THC’ is short for ‘delta-9-tetrahydrocannabinol’, and it’s what winds up in your system after you use marihuana), it has different effects on different metabolisms; in particular, you build up a tolerance to it over time. If you set an arbitrary limit on the amount of THC a driver can have in his or her system, you essentially make it legal per se to drive with less than that in your system. The authors fear this means that a good many people who are are impaired will get away with driving in that condition, because they have a low tolerance, but don’t meet the per se standard. Contrariwise, drivers who are seasoned marihuana users, and therefore can have a higher level of THC in their systems without being impaired, will be prosecuted, impaired or not.