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Differences in Cannabis Impairment and its Measurement Due to Route of Administration

NCJ Number
Date Published
December 2020
14 pages

This is the Final Summary Overview of a research project with the goal of improving knowledge of the pharmacokinetics and associated pharmacodynamics of cannabis administered via vaporization and oral consumption, in order to assess whether an individual under the influence of cannabis is impaired.


The project used a combination of behavioral and performance evaluations with forensic toxicology testing (blood, urine, and oral fluid) following controlled administration of known doses of cannabis. A total of 20 individuals who had not used cannabis for at least 30 days participated in six, double-blind, experimental sessions, with each separated by at least 1 week. Across all six sessions, each participant consumed cannabis brownies that contained 0 (placebo), 10, or 25 mg of THC or inhaled vaporized cannabis that contained 0 (placebo), 5, or 20 mg of THC. The findings of this research project indicate that THC is not a reliable marker of cannabis impairment. Many participants had low levels of THC in their blood and oral fluid at time-points during which they exhibited substantially decreased performance on cognitive and psychomotor assessments. After oral administration at 10 mg of THC, only two participants reached a blood THC level greater than or equal to 5 ng/mL. After oral administration at 25 mg THC, only six participants reached a blood THC level greater than or equal to 5 ng/mL.

Date Published: December 1, 2020