Cannabis and Tobacco Co-use Study


The purpose of this study is to better understand tobacco outcomes using a well-known stop smoking medication, varenicline, and financial incentives with tobacco users. The investigators are also interested in how cannabis/marijuana and tobacco interact during a tobacco quit attempt. All participants will receive tobacco cessation treatment (varenicline) for 12 weeks. This study will recruit adult tobacco users (ages 18-40) who are motivated to quit smoking cigarettes.

Full Title of Study: “A Prospective Trial of Varenicline and Incentives for Tobacco Cessation in Adults”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Non-Randomized
    • Intervention Model: Single Group Assignment
    • Primary Purpose: Treatment
    • Masking: None (Open Label)
  • Study Primary Completion Date: January 21, 2024

Detailed Description

Cannabis co-use among tobacco users is exceedingly common and rates of co-use appear to be increasing among adults in the US, which is consistent with overall increases in cannabis use rates among US adults. Given the current cannabis landscape, further increases in cannabis use are likely and may result in continued increases in the co-use of cannabis and tobacco.

Despite high rates of co-use, there is little consensus regarding treatment recommendations for this population and an understanding of the impact of co-use on successful cessation. The literature on the impact of co-use on tobacco cessation outcomes specifically has been mixed and fraught with limitations, including methodological variation, lack of biochemical verification to confirm cannabis use status and severity, and variations in study samples. Currently, no prospective studies have been conducted to evaluate the impact of cannabis use on tobacco cessation outcomes. Further, no studies have collected cannabis use changes during tobacco cessation treatment to assess for concurrent reductions, abstinence, or of greater concern, compensatory (i.e., increased) use as a result of tobacco reduction/abstinence.

This study is a prospective 12-week tobacco cessation trial using established methods and outcomes typical of tobacco cessation trials, but specifically recruiting co-users of cannabis. The aims of this proposed study are to; 1) examine the impact of cannabis co-use on tobacco cessation outcomes among co-users compared to tobacco only participants (Aim #1), 2) among cannabis co-users, assess changes in cannabis use during tobacco treatment (Aim #2), and 3) assess for a dose-dependent impact of cannabis co-use severity on tobacco cessation (Exploratory Aim #1).


  • Drug: Varenicline
    • Varenicline is a medication approved by the Food and Drug Administration for the treatment of tobacco use disorder among adults (ages 18 and over). In this study, all participants will be administered active medication for the recommended 12 week treatment period. The standard dose titration schedule will be used, which includes 0.5 mg once per day (q.d.) on Days 1-3, 0.5 mg twice per day (b.i.d.) on Days 4-7, and 1.0 mg b.i.d. starting on Day 8. Dosing of 2.0 mg per day will be maintained for the next 11 weeks, for a total of 12 weeks of active treatment for all study participants.
  • Behavioral: Contingency Management
    • Contingency management procedures will be implemented and financial incentives will be provided at weekly visits contingent on tobacco abstinence verified through urinary qualitative cotinine (starting at Week 2). A set amount of $20 per study visit will be delivered based on a negative qualitative urinary cotinine result.
  • Behavioral: Counseling
    • Psychosocial counseling will be administered by trained research staff leading up to the target quit date and throughout the study. Counseling will include motivational enhancement for medication adherence and tobacco cessation. The content of counseling will be skills-based and will focus on enlisting social support, recognizing smoking triggers, managing craving/withdrawal/stress, etc.

Arms, Groups and Cohorts

  • Other: Co-Use Group
    • Cannabis and tobacco co-use group.
  • Active Comparator: Tobacco Only Group
    • Tobacco only group.

Clinical Trial Outcome Measures

Primary Measures

  • 7-day point prevalence tobacco abstinence at the end of treatment (Week 12)
    • Time Frame: Final 7 days of treatment (Week 12)
    • 7-day point prevalence abstinence from tobacco at the end of treatment (Week 12) will be assessed via biochemical verification (urinary cotinine; ng/ml) and will be compared between cannabis co-users and tobacco only controls.

Secondary Measures

  • Changes in cannabis use during tobacco cessation treatment (among co-users)
    • Time Frame: Final 4 weeks of study treatment (Weeks 8-12)
    • Among cannabis co-users, cannabis use rates and amounts (based on urinary cannabinoids [ng/ml]) during the final 4 weeks of tobacco treatment (Weeks 8-12) will be assessed.

Participating in This Clinical Trial

Inclusion Criteria

1. Between the ages of 18 and 40 years old

2. Must be able to understand the study and provide written informed consent

3. Daily cigarette smoker for ≥ 6 months, smoking ≥ 5 cigarettes per day

4. Must submit a breath carbon monoxide (CO) sample of ≥ 7 parts per million (ppm) at the screening visit

5. Be interested in quitting smoking tobacco cigarettes (defined as a 5 or above on a 10-point Likert scale assessing interest in quitting [1=not at all interested, 10=extremely interested])

6. Must be willing to take varenicline for the standard 12-week course of treatment

7. If female, agreement to use birth control (any form) to avoid pregnancy during study procedures

Additional inclusion criteria will be implemented for cannabis co-users, which include:

8. Self-reported use of cannabis on at least 10 out of the past 30 days or submit a positive qualitative urinary cannabinoid test at screening (limit of detection is 50 ng/ml)

Exclusion Criteria

1. Any serious or unstable medical/psychiatric disorder (including severe substance use disorders, other than cannabis or tobacco use disorders) or other significant concern in the past three months that may interfere with study performance, impact participant safety, compliance with study procedures, or potentially confound the interpretation of findings

2. Currently pregnant, lactating, or contemplating pregnancy in the next 6 months

3. Current use of medications with smoking cessation efficacy

4. Use of any medications that would interfere with varenicline

5. No regular use of other tobacco or nicotine products other than combustible cigarettes (e.g., smokeless tobacco, electronic cigarettes, etc.) in the past month prior to screening

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 40 Years

Are Healthy Volunteers Accepted: No

Investigator Details

  • Lead Sponsor
    • Medical University of South Carolina
  • Collaborator
    • National Cancer Institute (NCI)
  • Provider of Information About this Clinical Study
    • Principal Investigator: Erin McClure, Principal Investigator – Medical University of South Carolina
  • Overall Official(s)
    • Erin McClure, Ph.D., Principal Investigator, Medical University of South Carolina
  • Overall Contact(s)
    • Patrick Cato, 843-792-4215,

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