Relating Individual Differences in Personality with Speed after Smoked Cannabis

Author(s): Wickens, Mann, Brands, Stoduto, Matheson, Sayer, Burston, Pan, Di Ciano, Kenney, Soule, Huestis, Le Foll

Slidedeck Presentation:

2A Wickens Rel Ind Diff



A recent study of the effects of smoked cannabis on the simulated driving of young recreational cannabis users observed that, compared to placebo, those driving after smoking cannabis demonstrated significant reductions in speed (Brands et al., 2019). Personality and individual differences have long been recognized as predictive of driving behaviour and outcomes, including impaired driving and collision risk (Richer & Bergeron, 2009). Moreover, it has been suggested that personality and individual differences may represent endophenotypic markers for addiction (i.e., a behavioural phenotype with an underlying genetic basis; Jupp & Dalley, 2014) and may affect behavioural and neurophysiological responses to drugs (Spronk et al., 2015).


This preliminary analysis examines the association of personality and individual differences with changes in driving speed after smoking cannabis.


Data were drawn from a sample of drivers aged 19-25 years who smoked cannabis 1-4 days per week. Participants were randomized to smoke an active (12.5% THC) or placebo (0.009% THC) cannabis cigarette ad libitum. The 61 participants randomly assigned to the active condition were considered in the current analysis. Assessments of blood THC level and simulated driving occurred at baseline and 30 minutes after cannabis exposure. Each driving assessment included two simulation trials, one under full attention and one under conditions of cognitive load (counting backwards by 3s). Difference scores were calculated for speed under both full attention and cognitive load conditions (mean speed at baseline subtracted from mean speed at 30 min post-cannabis exposure). Self-report measures of driver behaviour, personality, and individual differences (e.g., Eysenck Impulsivity Questionnaire, Driver Behaviour Questionnaire (DBQ), General Health Questionnaire) were administered prior to drug exposure. A series of three hierarchical linear regression models, with the initial block in each controlling for sex, mean speed pre-drug and blood THC level post-drug, were conducted to explore the relationship between personality or individual differences and changes in driving speed after cannabis exposure.


Across the hierarchical linear regression models tested, impulsivity significantly predicted the change in speed under both full attention (=-.45, p<.001) and cognitive load (=-.35, p=.008). Adjusting for baseline speed, sex, and blood THC level, increasing impulsivity was associated with greater reductions in speed after cannabis.


These regression analyses suggest that impulsivity may influence how driving behaviour is affected by cannabis use. Consistent with findings of more intense subjective effects of cannabis among individuals high in trait impulsivity (e.g., van Wel et al., 2015), the current study found that higher trait impulsivity scores were significantly associated with greater reductions in driving speed after cannabis use. This may suggest that individuals high in trait impulsivity may be more sensitive to the driving-related effects of cannabis.


More research is needed to understand the possible biological and genetic influences underlying the potential association between impulsivity and cannabis effects, as well as differences in frequency and patterns of and motivations for cannabis use among more impulsive users.

Insert full paper link