Effect of Cannabis on Cigarette Use Behavior

A full-factorial laboratory study will be conducted to determine the impact of acute THC administration on the dose-related motivational, subjective, and physiological effects of combustible cigarettes. This study will employ a double-blind, placebo-controlled, within-subjects crossover design to examine the dose-effects of THC on combustible tobacco use. The study will use multiple active doses of THC and placebo (0, 5, and 30 mg; corresponding to 0, 1, and 6 standard THC unit doses). Participants will be randomized to either smoked or vaporized THC administration using a between-subjects approach to evaluate the effect of congruent versus incongruent routes of THC and tobacco administration on study outcomes.

Inclusion criteria

• Healthy non-treatment seeking adults aged 21 or older
• Report daily use of combustible tobacco cigarettes
• Biological confirmation of cigarette use: have an expired carbon monoxide (CO) level of more than 5 ppm and a positive urine cotinine test at screening
• Report current use of cannabis (at least 1 occasion per week)
• Have experience with the inhalation route of administration for cannabis
• Biological confirmation of cannabis use: have a positive urinary THC drug test at screening.
• For women of children bearing potential and men with female partners of child-bearing potential, must be willing to use an effective form of contraception during the study.

Exclusion criteria

• Report current intention to reduce or quit cannabis or tobacco use within the next 30 days
• Meet Diagnostic and Statistical Manual (DSM-5) criteria for a substance use disorder other than alcohol, cannabis, or nicotine
• Test positive for illicit drugs other than cannabis and tobacco
• Positive breath alcohol test at study admission
• Have a current physical or mental illness judged by the study team to negatively impact participant safety or scientific integrity
• Have a lifetime history of suicidal behavior (i.e. past suicide attempt), or current suicidal behavior or ideation as assessed by the Columbia Suicide Severity Rating Scale (C-SSRS)
• Are currently pregnant, planning to become pregnant in the next three months or are currently breastfeeding
• Have a history of clinically significant cardiac arrhythmias or vasospastic disease (e.g., Prinzmetal's angina)
• Are currently enrolled in another clinical trial or have received any drug as part of a research study within 30 days of study participation.