Conventional Field Sobriety Tests Not Particularly Sensitive to Cannabis-Induced Impairment

Baltimore, MD: Neither subjects’ performance on conventional field sobriety tests nor the detection of THC in their blood are reliable indicators of cannabis-induced impairment, according to clinical trial data published in the Journal of Psychopharmacology

A team of investigators affiliated with the Johns Hopkins University School of Medicine and the Medical University of South Carolina assessed the effects of cannabis ingestion on a battery of behavioral and cognitive tests. Participants in the study were infrequent users of cannabis. Subjects vaporized cannabis flowers of varying potencies (low-THC, high-THC or placebo) and consumed THC-infused brownies (10 mg THC, 25 mg THC, or placebo). 

Researchers identified few behavioral or cognitive changes in performance associated with the ingestion of low-THC products, but they did identify changes associated with the consumption of higher-potency products. Nonetheless, subjects’ performance on conventional field sobriety tests, like the ‘walk-and-turn’ test and the one leg stand, “showed little sensitivity to cannabis-induced impairment” – a finding that is consistent with previous studies. Similarly, the detection of THC in subjects’ blood was also “a poor proxy of cannabis impairment” – a finding that is also consistent with prior research.

By contrast, authors acknowledged that the use of the mobile device performance application, DRUID, was adequately sensitive to cannabis-induced changes in subjects’ performance. NORML has frequently opined in favor of the use of performance testing technology as a more reliable indicator of cannabis-induced impairment. 

Investigators concluded: “Standard approaches for identifying impairment due to cannabis exposure (i.e. blood THC and field sobriety tests) have severe limitations. There is a need to identify novel biomarkers of cannabis exposure and/or behavioral tests like the DRUID that can reliably and accurately detect cannabis impairment at the roadside and in the workplace.”

Full text of the study, “Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis,” appears in the Journal of Psychopharmacology. Additional information on cannabis and driving performance is available in the NORML fact sheet, “Marijuana and Psychomotor Performance.