The objective of the proposed research is to investigate how smoking increasing potency of THC (i.e., the psychoactive ingredient in marijuana) changes tobacco cigarette smoking behavior, urges, subjective effects, and abuse liability. This study will be a within-subjects, placebo-controlled study in our clinical laboratory of the effect of active vs. placebo marijuana on cigarette puff topography, exhaled carbon monoxide, urge, subjective effects, and abuse liability among 7 adults who smoke both marijuana and tobacco cigarettes.

The study requires a total of three visits to Battelle's laboratory: one screening visit and two experimental visits. The screening visit will determine eligibility into the study. If eligible, participants will smoke a tobacco cigarette through the Clinical Research Support System (CReSS) puff topography device. Enrolled participants will attend two separate 5-hour experimental visits. Participants will be randomly assigned the order of THC potency (active or placebo), with the assignment blocked by sex. When participants arrive at the laboratory for each visit, they will provide biologic samples to verify compliance with pre-study instructions and then will be taken to a specially ventilated smoking chamber. They will be connected to a continuously-monitoring heart rate and blood pressure machine so that their vital signs can be observed throughout the smoking session. A research assistant will give a marijuana cigarette to the participant. A research assistant will light the cigarette and then exit the room. Participants will follow tape-recorded instructions for smoking the marijuana cigarette through the CReSS device. Upon completion of smoking the marijuana cigarette, participants will complete the Tobacco Craving Questionnaire via paper and pencil and will then be allowed to smoke one of his own tobacco cigarettes through the CReSS puff topography device. Participants will be allowed to smoke as many tobacco cigarettes as they would like for the next 3 hours. Participants will then be given lunch and sent home via taxicab. All participants will receive both potencies (i.e., active and placebo) of marijuana. The active potency of marijuana will be 5.6% THC.

Inclusion Criteria:

1. Current US resident;
2. Age ≥ 18 years;
3. Self-reported smoking of marijuana no more than three days per week within the past year;
4. Self-report past-month smoking of marijuana;
5. Self-report daily smoking of at least five cigarettes per day within the past year;
6. Cotinine ≥ 100 ng/mL at the in-person screening visit; and
7. Able to read, understand, and sign informed consent.

Exclusion Criteria:

1. Meets Diagnostic and Statistical Manual-5 (DSM-5) criteria for current (i.e., past year) or past (i.e., lifetime) cannabis use disorder;
2. Meets DSM-5 criteria for any current Axis I disorder, other than tobacco use disorder;
3. Self-reported current desire to stop marijuana or tobacco use, defined as 7 or greater on an 11-rung (scaled of 1-10) Contemplation Ladder for each;
4. Self-reported asthma or chronic obstructive pulmonary disease; and
5. Among females, current pregnancy or lactation.