Assessment of cognitive and psychomotor impairment, subjective effects, and blood THC concentrations following acute administration of oral and vaporized cannabis

Abstract

Background: Cannabis legalization is expanding, but there are no established methods for detecting cannabis impairment.

Aim: Characterize the acute impairing effects of oral and vaporized cannabis using various performance tests.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: Cannabis; cannabis edibles; cannabis vaporizers; impairment.

Figure 1.

Mean (+SEM) performance on cognitive/psychomotor tasks (change-from-baseline scores) over time in each experimental condition. BL=baseline time point; mg=milligrams THC. Filled symbols indicate significant difference from baseline within that experimental condition. Higher scores on the DAT and DRUID^® indicate worse performance (i.e. greater impairment), whereas lower scores on the DSST and PASAT indicate worse performance. Note this exact figure is presented in Supplemental material, but using raw data. Oral and vaporized cannabis dosing was completed immediately prior to “time 0.”

Figure 2.

Performance on the DRUID^® (i.e. global impairment scores) for each individual participant at baseline and post-cannabis administration (i.e. raw peak scores) in each experimental condition. Higher scores indicate worse performance (i.e. greater impairment). The dotted line (i.e. score of 57) signifies the threshold used to classify participants as “impaired”; this threshold was associated with a blood–alcohol concentration of 0.08% in a prior controlled alcohol dosing study (Richman and May, 2019). Peak scores were calculated for each respective route of administration within time frames previously shown to coincide with peak drug effects (i.e. 0–2h for vaporized conditions and 2–5h for oral conditions).

Figure 3.

Performance on individual field sobriety tasks (i.e. peak change-from-baseline clues) in each experimental condition. The y-axes indicate the number of participants (out of 20) who displayed a given number of clues, whereas the x-axes display the number of clues observed. More clues indicate worse performance (i.e. greater impairment). Two or more clues on a given test is indicative of impairment. The McNemar’s tests did not detect significant differences across dosing conditions in the number of individuals judged as “impaired” (based on the ≥2 clue criteria) for any of the tests (see Table 3). Note this exact figure is presented in Supplemental material, but using raw data.

Figure 4.

Mean (+ SEM) subjective ratings for visual analog scale (VAS) items “drug effect,” “trouble with memory,” and “difficulty with routine tasks” from the Drug Effect Questionnaire (DEQ) in each experimental condition over time. BL = baseline time point; mg = milligrams THC. Filled symbols indicate significant difference from baseline within that experimental condition. Oral and vaporized cannabis dosing was completed immediately prior to “time 0.”

Figure 5.

Mean (+SEM) heart rate (beats per minute; raw data) in each experimental condition over time. BL = baseline time point; mg = milligrams THC. Filled symbols indicate significant difference from baseline within that experimental condition. Oral and vaporized cannabis dosing was completed immediately prior to “time 0.”

Figure 6.

Mean (+SEM) blood THC concentrations (ng/ml) over time in each experimental condition. Note that blood specimens were not collected at hour 0 and hour 5 in oral dosing sessions and vaporized dosing sessions, respectively. Data are displayed for the 17 participants who had whole blood specimens collected. Oral and vaporized cannabis dosing was completed immediately prior to “time 0.”