Now there is a new study that adds to the evidence that a THC blood levels is not a good predictor of driving performance.

The study published in the journal Clinical Chemistry investigated the connection between THC blood levels and performance in a driving simulator. Even though THC blood levels of participants were often above some states’ “per se” or zero-tolerance limits, driving performance was no worse than those with blood levels below those limits. This suggests current THC per se driving laws may not accurately reflect actual driving impairment in frequent cannabis users.

In Kentucky, it is unlawful to drive under the influence of any drug that impairs driving ability. Cannabis is included in that definition, and Kentucky’s law equally applies to non-medical and patients registered in the state medical cannabis program. People who are observed by law enforcement to be unsafely driving may be pulled over and administered a field sobriety test. Kentucky’s implied consent law states that any person operating a car automatically consents to chemical tests if an officer has reasonable grounds to believe a DUI has occurred. To prove the presence of cannabis, investigators must obtain a warrant and collect a blood sample. There is no breath analysis test like there is for alcohol. Kentucky defines the upper limit of THC as 5 nanograms per milliliter (ng/mL) of blood. For reference, 1 nanogram is one billionth of a gram.