Combined and Separate Effects of Cannabis and Tobacco: Psychomotor, Subjective and Physiological Outcomes

Co-administration of cannabis and tobacco 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. The purpose of the present study will be to 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 state-of-the-art 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.


Eligibility Criteria:
Inclusion Criteria:

* • Adults aged 19 years to 45 years (to control for the effects of age on cognition)

  * Smoke or vape cannabis at least once a month but no more than 4 times a week (to avoid enrolling people with cannabis use disorder who may experience withdrawal when asked to abstain from cannabis)
  * Experience with smoked cannabis in the past year
  * Report use of at least 100 cigarettes in their lifetime to ensure familiarity with the tobacco used in the present study
  * Use of any nicotine (smoked, vaped, etc) in the past year
  * G2 or full G driver's licence for at least a year
  * Willing to abstain from alcohol and other drugs (other than drugs required for treatment of a medical condition) for 48 hours prior to study session
  * Normal heart rate and blood pressure as determined by the QI (because cannabis and tobacco increase heart rate)
  * Normal ECG (because cannabis and tobacco increase heart rate)
  * Willing to abstain from cannabis for 72 hours prior to the test session and from smoking tobacco for 12 hours
  * Willing to use an accepted form of contraception during the study (both males and females)
  * Past lifetime experience with co-use of cannabis or tobacco (either simultaneous or concurrent)
  * Provides written and informed consent

Exclusion Criteria:

* • Use of psychoactive medications or drugs

  * Current alcohol or other substance use disorder, including cannabis (as assessed with the SCID)
  * Current or past nicotine dependence (to avoid precipitating a relapse)
  * Withdrawal symptoms as assessed with the Marijuana Withdrawal Checklist \[57, 58\]
  * A score of less than 10 on the Clinical Institute Withdrawal Assessment for Alcohol (CIWA-Ar) \[59\]
  * Family history of schizophrenia or psychosis (to avoid giving cannabis to anyone with a predisposition to psychosis)
  * Respiratory illnesses (due to the smoked route of administration in this study)
  * Any serious medical condition precluding participation as judged by the responsible study physician
  * Pregnancy or breastfeeding
  * Negative urine screen for cannabis at eligibility assessment (to ensure experience with cannabis)
  * Neurological disorders that may affect cognitive function
  * Treatment-seeking for tobacco or cannabis use
  * Use of more than 5 cigarettes a day (to avoid confound of the effects of chronic smoking on measures)
  * Concomitant therapy with sedative-hypnotics or other psychoactive drugs (counter-indicated with cannabis)