As can be seen in , baseline testing showed no significant between-group differences in age or estimated intelligence. Despite attempts to match groups based on age, education and prior driving experience, women had an additional year of education (F = 9.1, p = < 0.01) and driving experience (F = 6.2, p = 0.02) compared to men. Although not statistically different, the increased age in women likely accounted for these differences (F = 3.7, p = 0.06). All analyses were conducted with the entire group of participants that completed the cigarettes and an age matched subsample; results did not differ. Not surprisingly, men weighed significantly more (F = 9.3, p < 0.01), reported consuming more alcoholic beverages per week (F = 4.0, p = 0.05) and spent more time playing video games (F = 3.8, p = 0.05) than women. Using the Dula Dangerous Driver Index, men rated themselves as having a more risky driving style in everyday life than women (F = 4.5, p = 0.04).
Demographic and Baseline Testing
A sex difference was evident in the number of participants willing to complete the entire cigarette; 96% of men completed the active cigarette, while only 55.6% of the women did so; all males completed the placebo cigarette while one woman (5.9%) did not complete the placebo cigarette. Twenty-five percent of men and twenty percent of the women who received and completed the active marijuana cigarette reported a highness rating of 5 or less. Although no significant differences in highness or heart rate were found for those who completed the cigarette versus those who did not, behavioral findings were attenuated by inclusion of all participants. While this did eliminate more women than men, only results from participants who completed the entire cigarette (n = 73) are reported in the remaining analyses.
As expected, highness ratings increased immediately after smoking the active cigarette and declined throughout the test session. Immediately following smoking, both male and female participants who received the active marijuana cigarette rated themselves as significantly higher [male M = 6.4 (SD 1.7); female M = 7.2 (SD 1.8)] than those who received the placebo [male M = 2.6 (SD 2.3); female M = 3.5 (SD 1.5); F = 65.1, p < 0.001]. Immediately after driving, in addition to the dose-related effect in which active marijuana [male M = 5.7 (SD 1.5); female M = 7.4 (SD 1.1)] was rated as significantly higher than placebo [male M = 2.0 (SD 2.0); female M = 2.9 (SD 1.8); F = 84.8, p < 0.001], a sex difference was observed for highness ratings in which women rated themselves as higher than men for both active marijuana and placebo [F = 4.6, p = 0.04 and F = 9.0, p < 0.005]. No sex by drug interaction was evident. A similar, expected, increase in heart rate following the active marijuana cigarette [male M = 113.5 (SD 24.8); female M = 115.5 (SD 21.3)] was seen for both sexes when compared to the placebo [male M = 75.3 (SD 13.5); female M = 78.3 (SD 11.2); F = 66.4, p < 0.001]. The statistical difference in heart rate was still evident after driving [active marijuana: male M = 95.7 (SD 20.2); female M = 93.9 (SD 14.6); placebo: male M = 68.5 (SD 10.9); female M = 70.8 (SD 7.0); F = 47.2, p < 0.001]. No sex differences or interactions of sex and drug were noted. Subjective ratings of sleepiness based on the Stanford Sleepiness Scale increased significantly in participants receiving the active cigarette, but not the placebo cigarette. This increase was not evident immediately after smoking [active marijuana: male M = 3.0 (SD 1.0); female M = 2.7 (SD 1.1); placebo: male M = 2.5 (SD 1.0); female M = 2.8 (SD 0.8); F = 0.5, p = 0.5] but was evident after driving [active marijuana: male M = 3.1 (SD 1.1); female M = 3.6 (SD 0.9); placebo: male M = 2.2 (SD 1.1); female M = 3.1 (SD 1.1); F = 6.0, p < 0.02]. There was a significant sex difference after driving, with males being less sleepy than females [F(1,71) = 4.6, p < 0.04]. No drug × sex interaction was evident in sleepiness. No significant difference in motivation levels were reported between the sexes or for groups receiving the placebo [male M = 5.5 (SD 1.4); female M = 6.3 (SD 0.9)] or active cigarettes [male M = 5.7 (SD 1.6); female M = 5.8 (SD 1.6); F = 0.94, p = 0.43]. Marijuana did not appear to protect against simulator adaptation syndrome (data not shown) and two female participants (one who received active marijuana and one who received a placebo) did become nauseated from the simulator.
As shown in , participants receiving the active and placebo cigarettes performed similarly on the baseline “uneventful” segment of the driving task and no sex differences were observed. No group differences were seen in the means or standard deviations of the mean speed or steering wheel position. During the “eventful” segments of driving, a within-subjects comparison of PASAT performance prior to smoking and during driving showed a trend in the interaction between placebo vs. active marijuana and practice vs. driving PASAT performance [F = 3.36, p = 0.07)]. Persons smoking the placebo cigarette showed an improvement in performance of the PASAT during the driving task, likely attributable to practice effects. Under the influence of marijuana, however, no differences were found between PASAT performance during practice testing and while driving. Participants who smoked active marijuana decreased their speed during this section of the drive, suggesting additional compensatory skills were used. While women performed significantly worse than men on the PASAT during both practice and driving administrations, no sex differences were observed in respect to driving performance or practice effects. No differences during the PASAT were seen in the standard deviation of speed, the mean steering wheel position or the standard deviation of the steering wheel position, suggesting the decrease in speed allowed participants to successfully compensate for the effects of marijuana. All participants safely went through the Go/No-Go task intersection while the light was yellow. No group differences in speed, steering position, time to first reaction or type of reaction were observed in response to passing the emergency vehicle. The frequency of dog and car incursions and the tactics used to avoid collisions were similar between groups, as was the mean speed of impact for those colliding. No sex differences or interactions of sex and drug were observed.
Driving Performance after Smoking
Because of the significant increase in Stanford Sleepiness Scale scores for those receiving the active marijuana cigarettes, follow-up Multivariate Analyses of Variance (MANOVA) were performed controlling for the rating of sleepiness after driving. No differences were seen in the mean speed during the baseline segment of driving [F = 1.77, p = 0.14], during the distracted driving section [F = 2.23, p = 0.08] or while passing the emergency response vehicle [F = 1.43, p = 0.20]. No significant effects were seen for speed at which participants collided with the dog and/or intersection incursion vehicle.