Researchers recently published an article in the medical journal Clinical Chemistry that suggests a marijuana breathalyzer might be the best way to test if someone has smoked marijuana before getting behind the wheel.
The researchers collected breath samples from subjects who had smoked marijuana and were able to detect THC, the psychoactive component of marijuana. All subjects tested positive for THC immediately after smoking. Interestingly, however, subjects who were “everyday smokers” tested positive for THC four hours after smoking. “Part-time” smokers, on the other hand, did not test positive for THC after four hours.
This means that a marijuana breathalyzer would be effective for testing whether someone has recently smoked marijuana. For the regular smokers, however, it’s more of the same news.
Currently in those states that allow recreational marijuana, the legal limit for a DUI based on marijuana is five nanograms of THC per milliliter of blood. The problem with this bright-line standard is that a person could have five nanograms of THC per milliliter of blood in their system weeks after smoking. Unlike alcohol, marijuana is fat-soluble and stays in the body much longer than alcohol even after the user’s high is long gone. In other words, someone could be perfectly sober weeks after smoking, yet still be arrested for a DUI if THC is found in their system.
Should California ever legalize marijuana, new standards would need to be developed. The purpose of DUI laws are to prevent impaired driving as the result of intoxication, not to punish someone who was intoxicated two weeks ago.
If a marijuana breathalyzer can test for intoxication, so be it. Certainly, if a breath test can determine if someone has smoked marijuana recently, there will be a higher correlation to intoxication. And it seems researchers are getting close. But until then, the current standards being used to determine a marijuana DUI have very little to do with whether that person can safely drive a vehicle.