As cannabis use becomes more common, law enforcement agencies need reliable ways to identify truly impaired drivers. A recent commentary by Thomas D. Marcotte and Robert L. Fitzgerald highlights key gaps in current detection methods and recommends improvements to roadside impairment assessments.
Current Detection Methods
Officers use driving observations, driver interviews, field sobriety tests (FSTs), Drug Recognition Expert (DRE) evaluations, and toxicology testing to assess impairment. No single test can determine cannabis impairment on its own, so officers rely on the totality of the evidence.
How Do Sober Drivers Perform?
Researchers still know surprisingly little about how unimpaired drivers perform on SFSTs and DRE evaluations. Some studies have found that sober individuals can appear impaired, raising concerns about false positives. The authors call for larger, blinded studies involving diverse participants.
Defining Impairment
A major challenge is that there is no universally accepted definition of cannabis-related driving impairment. Cannabis exposure does not always mean a driver is impaired, making it difficult to establish clear standards for testing and enforcement.
Researchers are exploring tools such as tablet-based cognitive tests, eye-tracking systems, pupillary assessments, and mobile EEG devices. While promising, these technologies must be thoroughly validated before widespread adoption.
Today’s Cannabis Products Matter
Many studies do not reflect the high-THC products, concentrates, vapes, and edibles commonly used today. Researchers also need to better understand how cannabis interacts with alcohol and other drugs, which are frequently involved in impaired-driving cases.
Toxicology Has Limitations
Unlike alcohol, there is no cannabis equivalent of a breathalyzer that reliably indicates impairment. THC can remain detectable in blood or oral fluid long after impairment has ended, meaning toxicology tests may indicate recent use but not current impairment.
The authors warn that knowledge of cannabis use or a positive THC test can influence how evidence is interpreted. Additional training can help officers and other professionals recognize and reduce confirmation bias during investigations.
Improving Future Research
The commentary emphasizes the need for more controlled studies, better reporting of accuracy measures, and stronger partnerships between researchers and law enforcement. Reliable validation is essential for determining whether current and emerging tools accurately identify impaired drivers.
Current methods provide valuable information, but important knowledge gaps remain. Continued research, better validation, and new evidence-based technologies will be critical to improving cannabis-impaired driving detection and enhancing roadway safety.
Source:
Marcotte, T. D., & Fitzgerald, R. L. (2025). Validation of methods for detecting driving under the influence of cannabis: paths forward. Journal of Studies on Alcohol and Drugs, 86(4), 510-514.
