The legalization of marijuana for medical and recreational purposes has revealed a serious issue in DUI enforcement. In the past, when marijuana was illegal throughout the United States, jurisdictions generally had zero tolerance laws for THC, the psychoactive compound in cannabis. That meant that being caught driving with any detectible amount of THC in your bloodstream resulted in DUI charges, regardless of whether you were actually impaired.
This is still the law in Tennessee and a number of other states. However, even here there are important legal issues on the line.
For example, what if someone goes to a state where cannabis is legal for recreational use and then comes back to Tennessee? Even if they only used the drug in the state where it was legal, they could still have THC in their system for 30 days or longer. Is it really illegal for them to drive for that entire period?
Or, what about travelers who were prescribed medical marijuana legally in their home state? They can’t use their medical marijuana once they enter Tennessee, but are they also barred from driving until there is no detectible amount of THC in their blood?
The fact is, THC remains in the system long after the “high” period has receded. Cannabis intoxication lasts approximately two hours from the last dose. THC persists in the body for far longer. Therefore, the mere presence of THC in the blood is not an indicator of impairment.
States struggle to define THC impairment
In some states where cannabis is legal, officials have tried to set a threshold for THC in the blood that corresponds with impairment. However, THC affects people differently and also affects routine users differently from novice users.
In Utah, it’s illegal to drive with any measurable amount of THC or any of its metabolites in your system. The penalty is a fine of $1,000 and up to six months in jail. State-approved users of medical marijuana can use their status as a defense.
One Utah lawmaker is unsatisfied that THC-impaired driving is only a Class B misdemeanor in that state, even in cases of crashes that result in serious injury or death. Currently, a felony charge requires evidence of actual impairment, not the mere presence of THC. He wants to change the law so that a person is legally considered impaired if they have two nanograms per milliliter of THC in their blood.
But there is no scientific basis to conclude that people with two nanograms per milliliter of THC in their blood are impaired.
Driving while high is dangerous and illegal, but the tests used to prove impairment need to be rooted in scientific fact, not wishful thinking.