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Assessment of Cognitive and Psychomotor Impairment, Subjective Effects, and Blood THC Concentrations Following Acute Administration of Oral and Vaporized Cannabis

NCJ Number
Date Published
May 2021

Since cannabis legalization is expanding without established methods for detecting cannabis impairment, this study characterized the acute impairing effects of oral and vaporized cannabis using various performance tests. 


Participants (N = 20, 10 men/10 women) who were infrequent cannabis users ingested cannabis brownies (0, 10, and 25 mg Δ-9-tetrahydrocannabinol, THC) and inhaled vaporized cannabis (0, 5, and 20 mg THC) in six double-blind outpatient sessions. Cognitive/psychomotor impairment was assessed with a battery of computerized tasks sensitive to cannabis effects, a novel test (the DRiving Under the Influence of Drugs, DRUID®), and field sobriety tests. Blood THC concentrations and subjective drug effects were evaluated. The study found that low oral/vaporized doses did not impair cognitive/psychomotor performance relative to placebo, but produced positive subjective effects. High oral/vaporized doses impaired cognitive/psychomotor performance and increased positive and negative subjective effects. The DRUID® was the most sensitive test to cannabis impairment, as it detected significant differences between placebo and active doses within both routes of administration. Women displayed more impairment on the DRUID® than men at the high vaporized dose only. Field sobriety tests showed little sensitivity to cannabis-induced impairment. Blood THC concentrations were far lower after cannabis ingestion versus inhalation. After inhalation, blood THC concentrations typically returned to baseline well before pharmacodynamic effects subsided. 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. (publisher abstract modified)


Date Published: May 1, 2021