Effect of Cannabis on Cigarette Use Behavior

Inclusion Criteria:

1. Healthy non-treatment seeking adults aged 21 or older

2. Report daily use of combustible tobacco cigarettes

3. Biological confirmation of cigarette use: have an expired carbon monoxide (CO) levelof more than 5 ppm and a positive urine cotinine test at screening

4. Report current use of cannabis (at least 1 occasion per week)

5. Have experience with the inhalation route of administration for cannabis

6. Biological confirmation of cannabis use: have a positive urinary THC drug test atscreening.

7. For women of children bearing potential and men with female partners ofchild-bearing potential, must be willing to use an effective form of contraceptionduring the study.

Exclusion Criteria:

1. Report current intention to reduce or quit cannabis or tobacco use within the next 30 days

2. Meet Diagnostic and Statistical Manual (DSM-5) criteria for a substance use disorderother than alcohol, cannabis, or nicotine

3. Test positive for illicit drugs other than cannabis and tobacco

4. Positive breath alcohol test at study admission

5. Have a current physical or mental illness judged by the study team to negativelyimpact participant safety or scientific integrity

6. Have a lifetime history of suicidal behavior (i.e. past suicide attempt), or currentsuicidal behavior or ideation as assessed by the Columbia Suicide Severity RatingScale (C-SSRS)

7. Are currently pregnant, planning to become pregnant in the next three months or arecurrently breastfeeding

8. Have a history of clinically significant cardiac arrhythmias or vasospastic disease (e.g., Prinzmetal's angina)

9. Are currently enrolled in another clinical trial or have received any drug as partof a research study within 30 days of study participation.