Perceived effects of cannabis: Generalizability of changes in driving performance

Abstract

Objective

The objective of this analysis was to determine the generalizability of the relationship between different samples of a driver’s perceived state after cannabis use and related performance while operating a motor vehicle.

Methods

Data were collected from 52 subjects in a study examining the effects of cannabis on driving performance. Data were analyzed using the SAS GLM Select procedure, using stepwise selection, with subjective effects, dosing condition (placebo vs. 6.18% delta-9-tetrahydrocannabinol [THC]), and driving context as independent measures. Correlation matrices of measures of driving performance against subjective responses and dosing condition used Pearson’s and Spearman’s test statistics, respectively. Results were compared to a prior study from a sample of 10 subjects.

Results

Subjective perceptions of acute cannabis impairment remain significant predictors of driving performance and explain individual variability in driving performance degradation as well as the data, beyond that which can be explained by acute use of cannabis alone. However, the significant subjective predictors of driving performance differ between the current and prior studies. To better understand these differences, correlations between subjective effects and performance measures were evaluated, which revealed that most correlations matched directionally (e.g., an increase in “good drug effect” was correlated with an increase in standard deviation of lane position [SDLP]). When there was a mismatch, 1 or more correlations were insignificant. Dosing condition and “stoned” were perfectly consistent; “high” and “sedated” contained 1 mismatch; and “anxious,” “good drug effect” and “restless” contained 3 or more mismatches.

Conclusions

The results indicate that across both studies, differences in the perceived effects of cannabis are reflected in changes in both lateral and longitudinal control beyond the acute effects of cannabis, which may help explain individual variability in response to acute intoxication. However, the generalizability of these findings is lacking, as shown by inconsistencies in when and where subjective effects were significant. Other factors such as frequency of use, usage type, the evolving profile of a cannabis user, as well as other individual differences should be considered to explain this additional variability.

Keywords:

• Driving
• cannabis
• objective performance
• perceived impairment

Data availability statement

The data that support the findings of this study are available from TLB upon reasonable request.

Additional information

Funding

The data for this analysis were collected with support from a Small Business Innovative Research Contract (75N95019C00052) from the National Institute on Drug Abuse (NIDA). IRB approval was granted under # 201911551. Research reported in this article was supported by the National Center for Advancing Translational Sciences and National Institutes of Health under Award Number U54TR001356. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.