Both the National Highway Traffic Safety Administration and the National Institute on Drug Abuse are still struggling with a manner in which drivers can be tested for cannabis use behind the wheel. Both the NHTSA and the NIDA have stated that marijuana impairment testing via current blood sampling is unreliable. There are several issues that make testing an individual for cannabis use that occurred just before or behind the wheel.
Cannabis is made up of a variety of different cannabinoids. Some of those are psychoactive and some are not. When cannabis is smoked or eaten, the psychoactive element, THC, enters the fat cells for storage. Over time, it is released back into the bloodstream and then evacuated through urine. This process is exactly what makes testing for DUI penalties difficult. Depending on the level of usage for any given individual, along with factors such as weight and fat percentages, it can remain in the system for anywhere from days to weeks to even months. The slow release of THC stored in the fat cells leads to a prolonged taper of excretion from the body.
Legal Limits in Illegal States
There are already a few states where legal limits have been instituted. While this isn’t due to impairment or intoxication of any kind, it is due to zero tolerance policies in states that aren’t yet legal. In those states, no one should have it in their system. To begin to determine the level of intoxication or impairment in an individual pulled for Cannabis DUI, first there would need to be behavioral test conducted. The DSM IV list some behavior criteria that law enforcement can use to determine cannabinoid intoxication. None of the criteria mentions blood levels.
Even though several U.S. states have implemented behavioral test to determine if a driver is under the influence of cannabis, the use of blood levels are only in addition to what was observed by the arresting officer. Given the complexity of the pharmacology of cannabis, and multitude of individual characteristics that determine the intoxication due to cannabis use, it will likely be a long time before we see this technology available to law enforcement.