Study Reveals THC Levels Are Unreliable Indicators of Driving Impairment

A recent study published in Traffic Injury Prevention has challenged the reliability of blood and saliva THC levels as indicators of driving impairment. Conducted by Australian researchers, the study involved 14 participants who consumed cannabis with varying THC and CBD concentrations. Their driving abilities were then tested using a simulator, and samples were taken at intervals to measure THC levels

The study's findings suggest that THC levels in blood and saliva do not consistently correlate with impaired driving abilities. Notably, nearly half of the participants displayed no driving impairment shortly after cannabis consumption, despite having high THC levels. Conversely, some showed impairment hours later when their THC levels had decreased, indicating that THC concentration alone is an unreliable measure of driving capability

Researchers highlighted the inadequacy of current legal limits for THC in distinguishing between impaired and sober drivers. "The limits imposed in blood or saliva often fail to differentiate between intoxicated and sober drivers," the study authors noted. They emphasized that THC concentrations do not reliably indicate the amount of cannabis consumed or the timing of consumption, making it challenging to assess impairment accurately

This study aligns with previous research, including a 2019 report by the Congressional Research Service, which found no consistent correlation between THC levels and driving impairment. The National Highway Traffic Safety Administration has also observed that using THC levels as evidence of impairment lacks scientific backing. These findings call into question the effectiveness of current THC-based legal limits for driving

Moving forward, the study suggests a need for alternative methods to assess cannabis-related impairment in drivers. As more regions legalize cannabis, understanding its impact on driving safety becomes increasingly important. Policymakers may need to explore new strategies to ensure road safety without relying solely on THC concentration limits. This shift could lead to more accurate assessments and fairer legal frameworks