Tennessee’s DUI statute defines driving under the influence of alcohol or drugs in two different ways. One way is well-established and contains an objective measure: an alcohol concentration measured by a blood or breath test as .08 or more.
The other way, however, is much more subjective. It involves driving while “under the influence of any intoxicant, narcotic drug, or drug producing stimulating effects on the central nervous system.”
Does this mean that you can be charged with DUI even when the substances you were taking were completely legal?
In theory, yes. If the state can show that you really were impaired by narcotic pain medication or barbital drugs, such as oxycodone or Xanax, the fact that those substances are legal is not a defense to the charges.
But this is a big if. In order to bring a valid DUI charge, the state still has to show that you were impaired. This can be more difficult to do than with alcohol because there is no accepted, objective test for drugs as there is with breath or blood tests for alcohol.
Lack of objective standards for drugged driving
Despite this limitation, arrests for drugged driving in Tennessee have been increasing in recent years.
To upgrade its capacity to try to show drug impairment, Tennessee law enforcement agencies have been expanding the state’s Drug Recognition Expert (DRE) program. DRE officers take a three-week training course to look for things like unusual pupil as indicators of intoxication that doesn’t involve alcohol.
The number of training courses for DREs in Tennessee has doubled since 2012. There are now more than 100 officers certified under the state DRE program and the Tennessee Highway Safety Office recognizes an officer annually as DRE of the year.
Taking meds not a defense, but prosecution must prove impairment
No matter how well trained DRE officers are, however, looking for signs like out-of-the-ordinary pupil dilation is not an objective standard like 0.08.
So yes, in theory you can be charged with DUI even for legal substances like cold medicine or a painkiller prescription. The fact that the substances are legal is not a defense. But for the charge to be valid, the prosecution still has to show you were actually impaired.