Testing for marijuana impairment is one of the bigger challenges brought on by state decriminalization of adult cannabis use.

Unlike alcohol, for which both standards and a technology solution exist in the form of the breathalyzer, testing for the presence of or impairment by cannabis is more complex.

“It’s not just a breathalyzer as with alcohol, an easy test. With cannabis, it’s a urine sample. It’s a much more invasive way of testing and it’s not immediate,” said Mark Turkalo, national education and public entity placement leader for Marsh LLC in New York.

There is also evidence that cannabis differs from alcohol in terms of impairment.

The National Institute of Justice, part of the U.S Department of Justice, supported researchers from RTI International, a research nonprofit, to study how levels of tetrahydrocannabinol — which produce the cannabis “high” — in the body correlate with performance on impairment tests and concluded that THC levels in biofluids were not reliable indicators of marijuana intoxication for study participants.

The researchers reported that the one leg stand, walk and turn, and balance tests were not sensitive to cannabis intoxication for any of the study participants.

A December 2021 University of Sydney study, which analyzed available studies on the relationship between driving performance and concentrations in blood and saliva of THC, showed results indicating that blood and oral fluid THC concentrations are relatively poor or inconsistent indicators of cannabis-induced impairment.

“Higher blood THC concentrations were only weakly associated with increased impairment in occasional cannabis users while no significant relationship was detected in regular cannabis users. This suggests that blood and oral fluid THC concentrations are relatively poor indicators of cannabis-THC-induced impairment,” said study lead author Danielle McCartney from the Lambert Initiative for Cannabinoid Therapeutics.

The lack of both rapid test technology and a reliable standard defining impairment may mean effective testing is still some ways off, said Paul Shives, vice president, safety services, with J.A. Montgomery Consulting in Parsippany, New Jersey. “It’s going to be awhile,” he said.