Combined and separate effects of cannabis and tobacco: Psychomotor, cognitive, subjective and physiological outcomes (CASE-CT).

Co-administration of cannabis and tobacco in a single cigarette is a common practice, but there is little experimental evidence aimed at understanding the reasons for this prevalence. Some preliminary evidence suggests that tobacco may actually counteract the cognitive-impairing effects of cannabis, and may also increase the subjective (‘liking’) effects of cannabis, but results are inconclusive. Further, there are no studies into the effects of tobacco on other cannabis-related harms such as driving, or on the ability of tobacco to alter the blood levels of THC, the chemical responsible for the psychoactive properties of cannabis. This study will evaluate the effects of tobacco, cannabis or combinations of tobacco and cannabis on driving, cognition, subjective effects and blood THC. Driving will be assessed using a high fidelity driving simulator that allows for the safe and objective measurement of the effects of intoxicating substances on driving. Participants will be regular users of cannabis and will be invited to the lab for four counterbalanced test sessions. In these test sessions they will drive the simulator and undergo cognitive tests before and after smoking: 1) cannabis; 2) tobacco; 3) cannabis + tobacco; or 4) placebo. Outcomes will be measured at several time points after smoking the product. Participants will also give blood for determination of levels of THC, and will complete subjective effects questionnaires both before and after smoking the cigarette. This study will be one of the first experimental laboratory studies of the reasons behind co-administration of tobacco and cannabis.

This study will be one of the first laboratory investigations into the effects of combinations of cannabis and tobacco. Co-use of tobacco and cannabis is a common practice yet little is known about its impact on driving, cognition and subjective experience. The inclusion of a control condition with tobacco only will also allow for one of the fist studies of the effects of nicotine on driving. This study will have important implication for public outreach; with legalization consumers have increased access to a variety of products but there is little research to help them guide their choices.

This study is funded by the Canadian Institute for Health Research (CIHR)