Close this search box.

Review: THC Detection In Bodily Fluids Not Correlated With Impairment

“Lawmakers would be advised to consider alternative legislative approaches to address concerns over DUI cannabis behavior.”

Neither the detection of THC nor its metabolites in blood, breath, urine, or saliva is predictive of behavioral impairment, according to a literature review published in the Journal of AOAC (the Association of Official Analytical Chemists) International.

Researchers affiliated with the University of California at Davis affirmed that there is “no direct relationship between impairment and THC concentrations” in subjects’ bodily fluids – a finding that is consistent with the opinions of numerous traffic safety groups, including the National Highway Traffic Safety Administration and the American Automobile Association.

The investigators further acknowledged, “Current methods that focus on THC and/or metabolite concentrations in blood, saliva, urine, or exhaled breath can lead to false-positive results for recent use due to the persistence of THC well outside of the typical 3-4-hour window of potential impairment following cannabis inhalation.”

Consequently, the study’s authors determined that per se traffic safety laws adopted in several states that criminalize drivers who test positive for trace levels of THC in their blood are “not supported by science,” and that they risk “wrongly accusing” motorists who are neither impaired nor have recently consumed cannabis.

Five states – Illinois, Montana, Ohio, Pennsylvania, and Washington – impose various per se limits for the detection of trace amounts of THC in blood while ten states (Arizona, Delaware, Georgia, Indiana, Iowa, Michigan, Oklahoma, Rhode Island, Utah, and Wisconsin) impose zero tolerant per se standards. In these states, it is a traffic safety violation to operate a vehicle with detectable levels of THC in blood – even absent any demonstrable evidence of psychomotor impairment.

NORML has long opposed the imposition of per se THC limits for motorists and has alternatively called for the expanded use of mobile performance technology like DRUID. In a peer-review paper published by the Humboldt Journal of Social Relations, NORML’s Deputy Director Paul Armentano wrote: “The sole presence of THC and/or its metabolites in blood, particularly at low levels, is an inconsistent and largely inappropriate indicator of psychomotor impairment in cannabis consuming subjects.

“Lawmakers would be advised to consider alternative legislative approaches to address concerns over DUI cannabis behavior that do not rely solely on the presence of THC or its metabolites in blood or urine as determinants of guilt in a court of law. Otherwise, the imposition of traffic safety laws may inadvertently become a criminal mechanism for law enforcement and prosecutors to punish those who have engaged in legally protected behavior and who have not posed any actionable traffic safety threat.”

This article was reprinted from NORML. Full text of the study, “Complexity of translating analytics to recent cannabis use and impairment,” appears in the Journal of AOAC International.Additional information is available from the NORML Fact Sheet, ‘Marijuana and Psychomotor Performance.’