With marijuana now legal for either recreational or medical use in the majority of states, drugged driving appears to be on the rise. Unfortunately, there is no straightforward way to test whether someone is actually impaired by marijuana. It's easy enough to test for the drug's metabolites, but those remain in the system for weeks, while the drug's "high" only lasts for a couple of hours. Law enforcement has been seeking a so-called 'pot breathalyzer" that could test for actual impairment, not just exposure to the drug.
In Iowa, we have what's called a "per se" drugged driving law. What this means is that a person is considered guilty of drugged driving if there is any detectable amount of cannabis in their system. Prosecutors do not need to prove actual impairment to win their cases.
That means that people who have used marijuana anytime in the past few weeks could be considered guilty of drugged driving. Since marijuana is illegal for all purposes in Iowa, however, the fact that they were not "high" at the time of driving is not a defense for most people.
When a person from another state is arrested for marijuana-impaired driving, however, they can present as a defense the fact that the substance was legally prescribed in their home state. It might also be a defense if an Iowan recently traveled to a cannabis-friendly state and used the drug legally there.
Things would be a lot more straightforward if there were an effective "pot breathalyzer" that could test for actual impairment, not just the presence of the drug. Recently, a California company called Hound Labs announced that it has developed just such a device. Several cities have agreed to field test the device this fall.
What Hound Labs' machine does is test for THC, the psychoactive compound in marijuana, in the breath. According to the company, finding THC in breath would clearly indicate that the subject has smoked marijuana within the previous few hours.
Until now there was no way to test for breath THC because, in breath, the compound is measured in parts per trillion. By contrast, alcohol in the breath is measured in parts per thousand. Hound Labs says that it took five years to develop a test sensitive enough to detect THC in breath.
From the defense point of view, there are many questions to be answered about how accurate the device may be and whether breath THC actually implies impairment. Scientists are still debating how to define marijuana impairment, after all.
Even if the device is found reliable, however, police in Iowa would more likely use this device to bolster their cases since actual impairment need not be proved.