Evaluating the Scientific Validity of Marijuana Impairment Testing

PISCATAWAY, NJ – A recent editorial published in the Journal of Studies on Alcohol and Drugs raises significant concerns regarding the scientific validity of current methods employed by law enforcement to detect marijuana-impaired driving. As marijuana legalization spreads across various states in the U.S., the urgency for reliable impairment testing has never been greater. Police departments have traditionally relied on officers trained as Drug Recognition Experts (DREs) to assess drivers suspected of being under the influence of drugs, including marijuana.

However, the current testing methodologies lack robust scientific backing. According to William J. McNichol, J.D., an adjunct professor at Rutgers University Camden School of Law and author of the perspective piece in the journal, these methods are often more subjective than objective, raising questions about their reliability. McNichol stated, "The DRE process is a product of 'police science'—techniques created by police officers for their work, lacking rigorous scientific validation."

DREs employ a series of physical and cognitive tests to evaluate impairment, including assessments of coordination, blood pressure, and pupil size. However, existing studies suggest that these evaluations may not be significantly more accurate than random chance. McNichol notes, "Few studies have determined how often DREs get it right, but the evidence indicates they are not much better than a coin toss."

Despite these concerns, the DRE program continues to receive federal funding, with over 8,000 officers trained nationwide, as reported by the International Association of Chiefs of Police. The lack of scientifically valid testing methods for marijuana impairment is particularly pressing in the context of evolving drug laws, where marijuana use is legal in many states.

In a related commentary, experts Thomas D. Marcotte, Ph.D., and Robert L. Fitzgerald, Ph.D., from the Center for Medicinal Cannabis Research at the University of California San Diego, echoed the call for scientific collaboration. They argue that the development of more effective, unbiased tools for detecting marijuana impairment is crucial for public safety. "Collaboration between law enforcement and independent scientists is essential to improve detection methods," they emphasized.

McNichol also highlighted a potential funding source for research into legitimate testing methods: taxes generated from legal marijuana sales. "The money is there, if only it can be allocated properly," he stated, advocating for a shift in resources to support the development of scientifically valid impairment tests.

As the legal landscape surrounding marijuana continues to evolve, the demand for credible and effective detection methods has become increasingly critical. The implications of unreliable DRE testing methods could jeopardize the safety of roadways and the integrity of the legal system. Addressing these challenges will require a concerted effort from law enforcement, researchers, and policymakers to establish a scientifically sound framework for evaluating drug impairment on the roads.

The urgency for accurate testing methodologies cannot be overstated. As McNichol concluded, "We can and must do better."

**References:** 1. McNichol, W. J. (2024). Perspective: Pseudoscience and the detection of marijuana-based impairment: We can and must do better. *Journal of Studies on Alcohol and Drugs*, 86(4), 503–509. https://doi.org/10.15288/jsad.24-00307 2. Marcotte, T. D., & Fitzgerald, R. L. (2025). Robust Validation of methods for detecting driving under the influence of cannabis: Paths forward. *Journal of Studies on Alcohol and Drugs*, 86(4), 510–514. https://doi.org/10.15288/jsad.25-00110