As cannabis becomes legal in an increasing number of states in the United States, public safety experts have expressed concern over the lack of effective tools to identify drivers under the influence of cannabis.

Unlike alcohol, which can be detected through a breathalyzer, cannabis is metabolized differently. Tetrahydrocannabinol (THC) remains in the body for days — or even weeks — even after the psychoactive effects have ceased, making it difficult to assess real impairment while driving.

Studies show that there is no precise correlation between the amount of THC in the blood and the ability to drive, raising doubts about the methods currently used.

Police science or reliable tool?

In the United States, police rely on drug recognition experts, known as DREs (Drug Recognition Experts), who apply protocols to assess drivers suspected of substance use.

This analysis involves physical tests, such as motor coordination, vital signs, muscle tone, and eye movements. The intention is to determine, based on these signs, whether the driver is one of the drivers under the influence of cannabis or another substance.

However, according to William J. McNichol, a law professor at Rutgers University, the DRE protocol is not supported by robust scientific evidence.

In an editorial published in the Journal of Studies on Alcohol and Drugs, McNichol classifies the method as a product of "police science" — techniques created by and for police officers, without clear empirical validation.

"The accuracy of DREs can be as low as a coin flip," he told Cannabis Health.

The model expands to the workplace

In addition to the streets, an adapted version of the DRE approach has been implemented in corporate environments: Workplace Impairment Recognition Experts (WIREs).

These professionals are trained to detect signs of impairment caused by drugs in the workplace. Although the goal is prevention, McNichol warns of the risks of inaccurate diagnoses in this context as well.

The expansion of the model without reliable scientific evidence increases the urgency for truly effective methods, especially with the growing number of drivers under the influence of cannabis on public roads.

Researchers advocate for collaboration between science and police

An additional commentary in the Journal of Studies on Alcohol and Drugs, signed by Thomas D. Marcotte, Ph.D., and Robert L. Fitzgerald, Ph.D., from the University of California, San Diego, reinforces the call for scientific validation.

The experts argue that it is essential to develop unbiased and accurate technologies to detect drivers under the influence of cannabis, preserving both public safety and individual rights.

Among the proposals are:

- Development of biomarkers and onboard sensors;

- Standardized psychomotor assessments;

- Transparency in validation tests;

- Collaboration between toxicologists and law enforcement.

- The authors also suggest that funding for these studies come from tax revenue from the legal sale of cannabis.

With information from Cannabis Health