Effects of THC and Alcohol on Driving Performance

Low blood concentrations of THC and alcohol appear to have a minimal effect on driving performance.However, there is a gap in the literature about the combined effects of THC and alcohol. There is little empirical evidence to determine whether the combination of THC and alcohol could be additive or multiplicative. This issue is particularly important when dealing with concentrations that are just below legal thresholds - it is important to identify if someone who may have consumed cannabis and alcohol, in quantities that do not exceed legal thresholds, may nonetheless be impaired to drive. Answering this question requires more research on the combined effects of THC and alcohol under tightly controlled experimental conditions. Hence, the purpose of this study is to determine the additive (or multiplicative) effect of standardized low doses of cannabis, in combination with low-doses of alcohol, on a number of outcome measures related to driving. The investigators will focus specifically on the effect of low blood concentrations of THC (0, 125, and 250 µg/kg) alone and in combination with low blood concentrations of alcohol (BAC 0%, .025%, and .049%). They shall determine the combined effect of THC and alcohol on physiological, cognitive, subjective measures of impairment, and simulated driving. This study will focus on younger adults because they have higher impaired driving rates than other age groups. As a secondary aim of the study, the investigators will examine whether previous driving and drug use history are correlated with driving decisions during the simulated drive and subjective measures. This study will contribute to the evidence base informing legislation, policy making, and law enforcement. This study is particularly timely given upcoming changes in legislation about cannabis, and because the combination of THC and alcohol, even below legal thresholds, may lead to impaired driving and crashes.

Participants will receive 125 µg/kg of THC in combination with blood alcohol concentrations of .025%.

Demerit points incurred for driving errors during a simulated a G2 exit exam (the final step in Ontario's graduated licensing framework) on a STISIM Drive 3-screen driving simulator; demerit points will be assigned in real-time by a member of the research team based on the Ontario Ministry of Transportation scoring scheme

Continuous heart rate in beats per minute via 3-lead electrocardiography recording; will allow for calculation of heart rate variability)

Median Response Time and Efficiency in Alerting, Orienting & Executive Attention as Measured by the Attention Network Test (in milliseconds)

A computerized test to measure participants' performance in three separate components of attention: alerting, orienting, and executive attention

Perceptual Motor Speed & Efficiency as Measured by Time (in seconds) to Complete Trail Making Tests A&B

Ratings of participants' current perceptions of mood and bodily sensations (22 items including anxiety, alertness, dizziness, dry mouth) driving (3 items related to current willingness to drive), and subjective impairment (at time 2 only; 6 items related to strength of effects, perceived performance on tests); all items measures from not at all>extremely or absent>severe on a 100 mm line

Inclusion Criteria: BMI >18 and <30 valid G2 or G Ontario driver's license live on-campus or within 15 minutes drive of campus speak fluent English Exclusion Criteria: history of cardiovascular or psychiatric disorders current use of psychoactive medication current drug or alcohol abuse problem positive drug screen BAC level > .000%