Smoked cannabis' psychomotor and neurocognitive effects in occasional and frequent smokers

Abstract

Δ9-Tetrahydrocannabinol (THC), the primary psychoactive constituent in cannabis, impairs psychomotor performance, cognition and driving ability; thus, driving under the influence of cannabis is a public safety concern. We documented cannabis' psychomotor, neurocognitive, subjective and physiological effects in occasional and frequent smokers to investigate potential differences between these smokers. Fourteen frequent (≥4x/week) and 11 occasional (<2x/week) cannabis smokers entered a secure research unit ∼19 h prior to smoking one 6.8% THC cigarette. Cognitive and psychomotor performance was evaluated with the critical tracking (CTT), divided attention (DAT), n-back (working memory) and Balloon Analog Risk (BART) (risk-taking) tasks at -1.75, 1.5, 3.5, 5.5 and 22.5 h after starting smoking. GLM (General Linear Model) repeated measures ANOVA was utilized to compare scores. Occasional smokers had significantly more difficulty compensating for CTT tracking error compared with frequent smokers 1.5 h after smoking. Divided attention performance declined significantly especially in occasional smokers, with session × group effects for tracking error, hits, false alarms and reaction time. Cannabis smoking did not elicit session × group effects on the n-back or BART. Controlled cannabis smoking impaired psychomotor function, more so in occasional smokers, suggesting some tolerance to psychomotor impairment in frequent users. These data have implications for cannabis-associated impairment in driving under the influence of cannabis cases.

Figure 1.

Mean (standard deviation) for critical tracking task (lambda-c) and divided attention (Control losses, tracking error, hits, false alarms and reaction time) for 14 frequent and 8 (CTT) or 11 (DAT) occasional cannabis smokers following controlled smoking of a 6.8% THC (54 mg) cannabis cigarette.

Figure 2.

Mean (standard deviation) for accuracy, reaction time and errors of commission on the n-back for 14 frequent and 10 occasional cannabis smokers following controlled smoking of a 6.8% THC (54 mg) cannabis cigarette.

Figure 3.

Mean (standard deviation) Visual Analog Scale (VAS) score for 14 frequent and 11 occasional cannabis smokers following controlled smoking of a 6.8% THC (54 mg) cannabis cigarette.

Figure 4.

Median VAS scores in function of THC concentrations for 14 frequent and 11 occasional cannabis smokers following controlled smoking of a 6.8% THC (54 mg) cannabis cigarette.

Figure 5.

Mean (standard deviation) physiological measures for 14 frequent and 11 occasional cannabis smokers following controlled smoking of a 6.8% THC (54 mg) cannabis cigarette.