Impaired driving tests for THC are unreliable: study

Published on February 25, 2021 by oz. staff

The quest for an effective roadside cannabis test has been elusive.

New research adds further evidence that conventional solutions aren’t going to work.

A new simulated driving study published this month has found that setting a limit for cannabis and driving and testing for THC in a person’s mouth or blood during enforcement (aka roadside test) are not reliable indicators of driving impairment.

Researchers from The University of Sydney in Australia as well as Baltimore-US based Johns Hopkins University School of Medicine found these types of tests were unable to accurately assess when or how much cannabis has been taken by an individual.

Unlike blood alcohol concentration limits with alcohol, there is an inconsistency between impairment and THC concentrations.

The authors of the study conclude:

There appears to be a poor and inconsistent relationship between magnitude of impairment and THC concentrations in biological samples, meaning that per se limits cannot reliably discriminate between impaired from unimpaired drivers. There is a pressing need to develop improved methods of detecting cannabis intoxication and impairment.

Here’s the study abstract.