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.