Tests to detect marijuana-impaired driving are based on 'pseudoscience,' argue researchers

OG Article  edited by Stephanie Baum, reviewed by Robert Egan Watch Today's LIVE Episode on YouTube, X, and Rumble

June 30, 2025

For years, U.S. police departments have employed officers specifically trained to be experts in identifying impaired driving. The core issue, however, is that the methods these officers utilize lack a scientific foundation, as highlighted in a recent editorial in the Journal of Studies on Alcohol and Drugs (JSAD).

Consequently, law enforcement relies on subjective tactics: roadside tests and further evaluations by police officers designated as Drug Recognition Experts (DREs). These officers adhere to a standardized protocol purportedly capable of detecting drug impairment and even pinpointing the specific drug type, including cannabis.

The DRE process encompasses numerous steps, such as physical coordination assessments, checking the driver's blood pressure and pulse, evaluating muscle tone by squeezing the driver's limbs, and examining pupil size and eye movements.

Despite appearing to be a scientific approach, this protocol isn't actually supported by evidence of its effectiveness, states William J. McNichol, J.D., an adjunct professor at Rutgers University Camden School of Law and author of the perspective.

Instead, McNichol explains, the DRE process is a product of "police science"—techniques developed by law enforcement for their own operational use. Few scientific studies have attempted to ascertain the accuracy of DREs. However, the existing evidence suggests their performance is "not much better than a coin toss," McNichol observes.

Nevertheless, DRE programs and training receive federal funding, and over 8,000 DREs are currently employed in police departments nationwide, according to the International Association of Chiefs of Police. McNichol also points out that a "spinoff" of the DRE program has recently emerged in workplaces: Workplace Impairment Recognition Experts (WIREs), certified to detect and prevent on-the-job drug impairment.

Not long ago, when cannabis was uniformly illegal in the U.S., individuals faced severe consequences for simple possession or use. Now that it's legal in many states, McNichol stresses the urgent need for scientifically validated, reliable methods for detecting cannabis impairment. This, he adds, will necessitate involvement from scientists in the substance abuse field.

A related commentary in the same JSAD issue echoes this sentiment. Collaborations between law enforcement and scientists who are impartial—neither supporting nor refuting the status quo—represent the optimal path forward, write 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.

"Developing more robust tools to identify cannabis-impaired drivers in an unbiased fashion is essential to keeping our roadways safe," they assert. These authors also offer recommendations for enhancing the detection of drug-impaired driving.

Regarding funding for such research, McNichol suggests an existing source: taxes derived from legal cannabis sales.

"The money is there," he states, "if only it can be allocated properly."

For years, U.S. police departments have employed officers specifically trained to be experts in identifying impaired driving. The core issue, however, is that the methods these officers utilize lack a scientific foundation, as highlighted in a recent editorial in the Journal of Studies on Alcohol and Drugs (JSAD).

Consequently, law enforcement relies on subjective tactics: roadside tests and further evaluations by police officers designated as Drug Recognition Experts (DREs). These officers adhere to a standardized protocol purportedly capable of detecting drug impairment and even pinpointing the specific drug type, including cannabis.

The DRE process encompasses numerous steps, such as physical coordination assessments, checking the driver's blood pressure and pulse, evaluating muscle tone by squeezing the driver's limbs, and examining pupil size and eye movements.

Despite appearing to be a scientific approach, this protocol isn't actually supported by evidence of its effectiveness, states William J. McNichol, J.D., an adjunct professor at Rutgers University Camden School of Law and author of the perspective.

Instead, McNichol explains, the DRE process is a product of "police science"—techniques developed by law enforcement for their own operational use. Few scientific studies have attempted to ascertain the accuracy of DREs. However, the existing evidence suggests their performance is "not much better than a coin toss," McNichol observes.

Nevertheless, DRE programs and training receive federal funding, and over 8,000 DREs are currently employed in police departments nationwide, according to the International Association of Chiefs of Police. McNichol also points out that a "spinoff" of the DRE program has recently emerged in workplaces: Workplace Impairment Recognition Experts (WIREs), certified to detect and prevent on-the-job drug impairment.

Not long ago, when cannabis was uniformly illegal in the U.S., individuals faced severe consequences for simple possession or use. Now that it's legal in many states, McNichol stresses the urgent need for scientifically validated, reliable methods for detecting cannabis impairment. This, he adds, will necessitate involvement from scientists in the substance abuse field.

A related commentary in the same JSAD issue echoes this sentiment. Collaborations between law enforcement and scientists who are impartial—neither supporting nor refuting the status quo—represent the optimal path forward, write 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.

"Developing more robust tools to identify cannabis-impaired drivers in an unbiased fashion is essential to keeping our roadways safe," they assert. These authors also offer recommendations for enhancing the detection of drug-impaired driving.

Regarding funding for such research, McNichol suggests an existing source: taxes derived from legal cannabis sales.

"The money is there," he states, "if only it can be allocated properly."