Field Sobriety Tests “Unreliable Indicators of Marijuana Intoxication”

Laws regarding driving under the influence (DUI) of cannabis vary state to state, with a growing trend toward “per se” laws that use a level of THC in the blood, urine, or oral fluid as an indicator of driver intoxication. However, little evidence correlates a specific THC level with impaired driving, making cannabis per se laws controversial and difficult to prosecute.

In an effort to better understand marijuana intoxication and, ultimately, improve marijuana intoxication legislation, researchers supported by the National Institute of Justice from RTI International studied how specific cannabis doses and administration methods (eaten or vaped) affect THC levels in the body and how that correlates with performance on impairment tests.

Results from the clinical dosing sessions showed that THC levels in study participants’ biofluids varied depending on marijuana dose and administration method and that timing of maximum impairment for each dose – and performance on impairment tests – also varied by dose and administration method.

The RTI team concluded that, “although THC has been proven to affect areas of the brain that control movement, balance, coordination, memory, and judgment, – skills required for safe driving – THC levels in biofluids were not reliable indicators of marijuana intoxication.”