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.