Cannabis and alcohol are two of the most commonly used drugs in the world and are often used concurrently
(i.e., “co-used”). When used independently, both cannabis and alcohol can impair psychomotor skills, attention,
and cognitive functioning and ultimately, negatively impact driving performance and functioning in the
workplace. Prior laboratory studies have shown that cannabis/alcohol co-use can produce additive effects on
impairment, over and above impairment caused by either substance alone, and epidemiological studies show
that the risk for car accidents is significantly increased when a person has used both cannabis and alcohol.
Importantly, previous controlled studies on cannabis/alcohol co-use have focused almost exclusively on
smoked forms of cannabis, but many novel cannabis products have emerged in recent years. In our prior
laboratory studies, we have found that the acute effects of oral cannabis products (“edibles”) and cannabis
vaporizers (two popular novel forms of cannabis), differ markedly from smoked cannabis. These findings
suggest that oral and vaporized cannabis may interact with alcohol in distinct ways from smoked cannabis.
The aim of this project is to systematically evaluate the acute impairing effects of cannabis and alcohol, when
administered alone and together, in two human laboratory studies that will utilize rigorous double-blind, double-
dummy, placebo-controlled designs. The studies will differ by route of cannabis administration (Study 1: oral;
Study 2: vaporized), but will otherwise use essentially the same protocol. In each study, participants will
complete 7 outpatient drug administration sessions in which they self-administer placebo or active cannabis
(10 or 25 mg THC) and a placebo drink or alcohol drink calculated to produce a breath alcohol concentration
(BAC) of 0.05%. Participants will also complete a positive control session in which they administer placebo
cannabis and alcohol for a target BAC of 0.08% (the legal threshold, or “per se limit,” for driving impairment in
most U.S. states). Sessions will be completed in a randomized order and separated by at least one week.
Assessments will include a state-of-the-art driving simulator, a battery of cognitive/psychomotor performance
tasks, field sobriety tests, and subjective drug effect questionnaires. This research can inform impairment
detection standards for individuals who have co-used cannabis and alcohol (e.g., determine if 0.08% BAC is a
suitable alcohol intoxication threshold if a person has also used cannabis) which can inform whether there is a
need to adjust BAC per se limits in locations where cannabis is legal. Moreover, this study will evaluate a
promising novel cannabis impairment detection tool (the DRUID app) which could be invaluable to public safety
because current approaches to identifying cannabis impairment (e.g., per se limits for blood THC) are largely
ineffective. Lastly, these findings will help guide regulatory decisions concerning the allowance of commercial
establishments that sell both alcohol and cannabis as well as products that contain both alcohol and THC.