Scientific Review: Oral Fluid Testing “Not Ideal” for Determining Cannabis Exposure or Impairment

OG Article

• by NORML

• Posted on May 23, 2025

Oral fluid (OF) tests do not provide reliable information regarding when subjects last consumed cannabis or whether they are under its influence, according to the results of a meta-analysis published in scientific journal Heliyon.

Researchers affiliated with the Canadian Institute for Substance Use Research at the University of Victoria in British Columbia assessed data from seven studies involving 116 subjects.

They reported that OF tests frequently produced disparate results, even when subjects consume the similar quantities of cannabis. “Research shows a high degree of variability in THC concentrations for subjects given the same amount of cannabis,” investigators reported. “This variability produced some very high outliers in terms of THC concentrations and detracts from OF tests as a valid tool.”

Researchers further acknowledged that subjects who inhale cannabis are far more likely to test positive on oral fluid tests as compared to those who orally ingest marijuana-infused products. They also acknowledged that some subjects can test positive past cannabis exposure for more than 24 hours after smoking, long after any reasonable period of intoxication has worn off.

“We conclude from our meta-analysis that validity is not ideal for either detection of prior use or impairment at a commonly used THC cut-off of 1 ng/mL,” the study’s authors concluded. “OF tests should not be considered a valid indicator of [cannabis-induced] impairment.”

In 2023, federal transportation regulators passed new rules providing commercially licensed drivers the option of undergoing oral fluid testing as an alternative to mandatory urinalysis testing. However, to date those rules have not yet been adopted in the federal workplace.

NORML has repeatedly argued that employers should not presume that the detection of either THC or its metabolites in bodily fluids – including blood, urine, or saliva – is evidence of impairment. That is because their presence is not predictive of diminished performance. Alternatively, NORML has called for the expanded use of performance-based tests, like DRUID or Predictive Safety’s AlertMeter, which compare subjects’ cognitive skills to either their own prior performance or an aggregate baseline.