A Canadian study combining CT scans, xenon MRI, lung function tests, and airway cell analysis found that heavy cannabis smokers had worse respiratory symptoms, lower lung function, and overproduction of mucus-related genes.
Anyone who smokes cannabis regularly, pulmonologists, respiratory researchers studying non-tobacco inhalation exposures.
What the researchers found
The CANUCK study examined 139 cannabis smokers (categorized by joint-year exposure: low ≤5, moderate 5–20, high >20 joint-years) alongside 57 never-smokers, using an unusually comprehensive battery of tests.
Cannabis smokers at all exposure levels reported worse respiratory symptoms than never-smokers. High joint-year smokers showed lower pre-bronchodilator FEV1 — the standard measure of airflow obstruction — suggesting measurable lung function decline with heavy, long-term use.
The study went beyond standard pulmonary testing. Hyperpolarized xenon-129 MRI revealed ventilation abnormalities, and chest CT showed structural changes. At the cellular level, airway epithelial brushings from bronchoscopy demonstrated upregulation of immune response signatures and mucin genes. Air-liquid interface cell cultures confirmed elevated MUC5AC protein — a mucus component associated with airway disease — and its expression correlated with clinical symptoms.
A notable complication: 84% of cannabis-smoking participants reported current or former cigarette smoking or vaping, making it difficult to isolate cannabis-specific effects from tobacco co-exposure.
Why it matters
This is one of the most methodologically comprehensive studies of cannabis smoking's respiratory effects. Most prior research relied on questionnaires and basic spirometry. By adding advanced imaging (xenon MRI), cellular analysis (bronchoscopic brushings), and molecular data (gene expression, protein quantification), the CANUCK study provides multiple converging lines of evidence that cannabis smoking affects the airways at structural, functional, and molecular levels.
The numbers in context
139 cannabis smokers, 57 never-smokers. Exposure groups: ≤5, 5–20, >20 joint-years. 48% male, median age 27. 84% reported concurrent cigarette/vaping history. High-exposure group showed lower pre-bronchodilator FEV1. Elevated MUC5AC protein in airway cultures correlated with symptoms.
How the study worked
Cross-sectional study of 139 cannabis smokers and 57 never-smokers. Multi-modal assessment: respiratory symptom questionnaires, spirometry, chest CT, hyperpolarized xenon-129 MRI, bronchoscopic airway epithelial brushings with transcriptomic analysis, and air-liquid interface cell cultures for MUC5AC protein quantification.
Who was studied
N=196 participants (139 cannabis smokers, 57 never-smokers), median age 27 years, Canada.
What this study cannot tell us
Cross-sectional design cannot establish causation or track progression over time. The 84% tobacco/vaping co-use rate makes it difficult to attribute findings specifically to cannabis. Participants were relatively young (median 27), so long-term consequences may not yet be manifest. The study recruited from a single Canadian center, limiting generalizability.
How to read the evidence
Cross-sectional study with exceptionally comprehensive methodology (CT, xenon MRI, bronchoscopy, transcriptomics) — strong multi-modal evidence but limited by cross-sectional design and high co-use rates.
When this study was published
Published in 2026 in the European Respiratory Journal, enabled by Canada's cannabis legalization and representing the current frontier of cannabis respiratory research.
The bigger picture
The respiratory effects of cannabis smoking have been studied less rigorously than tobacco, partly because cannabis was illegal in most research settings until recently. Canada's 2018 legalization enabled studies like CANUCK. The finding that mucin gene upregulation and MUC5AC overproduction occur in cannabis smokers echoes pathways well-established in tobacco-related COPD — raising the question of whether heavy cannabis smoking could follow a similar trajectory to chronic lung disease. The smoking-versus-vaping comparison (RTHC-00231) and the cardiovascular data (RTHC-00237) add additional dimensions to the inhalation risk picture.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- Do the molecular changes in airway cells progress to clinically significant COPD with continued cannabis smoking? Would exclusive cannabis smokers (without tobacco history) show the same patterns? Does switching from smoking to vaping cannabis reverse the mucin gene upregulation?
Read the original research
Clinical, physiological, imaging and molecular responses to cannabis smoking: the Canadian Users of Cannabis Smoke (CANUCK) study.
The European respiratory journal, 67(1)
The European Respiratory Journal is a well-respected journal focusing on respiratory medicine.
Citation
Leung, Clarus; Gilchrist, Cassie L; Wang, Carolyn J; Liggins, James A; Li, Xuan; Yang, Julia; Cheung, Chung Y; Gerayeli, Firoozeh V; Singhera, Gurpreet K; Hsu, Wu Jih; Lidher, Lavraj S; Moo, Karolina; Leyson, Eleazar; Dhillon, Satvir S; Shaipanich, Tawimas; Leipsic, Jonathon A; Guenette, Jordan A; Rayment, Jonathan H; Kirby, Miranda; Gershon, Andrea S; Sadatsafavi, Mohsen; Tan, Wan C; Parraga, Grace; Carlsten, Christopher; Eddy, Rachel L; Sin, Don D; Leung, Janice M. (2026). Clinical, physiological, imaging and molecular responses to cannabis smoking: the Canadian Users of Cannabis Smoke (CANUCK) study.. The European respiratory journal, 67(1). https://doi.org/10.1183/13993003.01659-2025
Explore the wider topic
- Surviving 4/20 Sober: A Practical Survival Guide
- CBT for Cannabis Recovery: How Cognitive Behavioral Therapy Works
- Cannabis and Your Cardiovascular System: Heart Risk, Stroke, and What the Research Shows
- Cannabis and Your Heart: What the Cardiovascular Research Shows
- The Cannabis Relapse Cycle: Quit, Feel Good, Get Complacent, Repeat
- Cold Turkey vs Tapering: Which Way to Quit Weed
- Coughing Up Black Stuff After Quitting Weed: What It Means
- Dating Sober After Years of Being High: What Nobody Tells You
- Exercise as Medicine: Working Out After Quitting Weed
- Grieving Weed Itself: Mourning the Loss of a Companion
- How to Help Someone Quit Weed (When They're Not Ready)
- How to Quit Weed: A No-Judgment Step by Step Guide
- Journaling Through Weed Withdrawal: Why Writing Helps You Heal
- Lung Recovery After Quitting Weed: The Complete Timeline
- Weed and Your Lungs: Recovery Timeline After Quitting
- MA vs SMART Recovery vs Therapy: Comparing Your Options
- Meditation and Mindfulness for Weed Withdrawal
- Your Partner Still Smokes Weed: How to Navigate It
- Quitting Weed While Your Partner Still Smokes
- The Pink Cloud Effect: When Quitting Weed Feels Too Good
- How to Quit Smoking Weed Cold Turkey: What to Expect
- Quit Weed or Cut Back: Which Is Right for You?
- I Quit Weed and Regret It: An Honest Look at Non-Linear Recovery
- Quitting Weed in Your 20s: Career, Social Life, Starting Over
- Quitting Weed in Your 30s: It's Not Too Late
- Quitting Weed After 10+ Years of Daily Use: What to Expect
- Quitting Weed During a Life Crisis: Divorce, Job Loss, and Other Bad Timing
- Quitting Weed and Working Out: How Exercise Helps Recovery
- Quitting Weed as a Woman: Hormones, Cycles, and Recovery
- Quitting Weed After Loss: When Grief Comes Flooding Back
- Quitting Weed When It's Legal Everywhere
- Weed Withdrawal Success Stories: Real People Who Made It Through
- Quitting Weed Long Distance: When You Can't Remove Triggers
- Cannabis, Weight, and Diet: What Quitting Does to Your Appetite
- I Relapsed on Weed. Now What? A Practical Reset Guide
- I Relapsed After Quitting Weed: What Now?
- Sex After Quitting Weed: What Changes and What Doesn't
- Should I Quit Weed? A Decision Framework (Not a Lecture)
- Quitting Weed at Music Festivals and Concerts: A Sober Survival Guide
- Supplements That Actually Help with Weed Withdrawal (And Ones That Don't)
- How to Tell Your Friends You're Quitting Weed
- Cannabis and Driving: DUI Laws, Impairment Science, and What You Need to Know
- Weed and Acne: Can Quitting Cannabis Clear Your Skin?
- Weed and Fertility: What Couples Should Know
- Weed and Your Gut: How Cannabis Affects Digestion
- Weed and Your Heart: Cardiovascular Effects and Recovery
- Relapse Prevention Plan for Cannabis: A CBT-Based Approach
- Why Weed Relapse Happens: The Science Behind Going Back
- Replacing the Ritual: What to Do When You Quit Weed
- How Cannabis Damaged My Relationships: Before and After
- Social Media Detox from Weed Content
- Weed, Testosterone, and Male Health: What the Research Actually Shows