Cannabis smoking causes bronchitis but a surprisingly different lung pattern than tobacco | Research

The takeaway

Despite causing bronchitis at relatively low exposure, cannabis smoking produces a distinct respiratory pattern from tobacco: increased airway resistance and lung hyperinflation but no clear evidence of COPD, emphysema, or lung cancer.

Pulmonologists, primary care providers counseling cannabis users, respiratory researchers

Cannabis causes bronchitis but no convincing evidence of COPD or lung cancer

What the researchers found

Cannabis smoking causes bronchitis and increases central airway resistance with lung hyperinflation and higher vital capacity. Unlike tobacco, there is no convincing evidence it causes COPD, despite some case reports of bullous disease and pneumothorax in heavy users. An association with lung cancer remains unproven with conflicting findings.

Why it matters

With cannabis legalization increasing smoking prevalence, understanding its distinct respiratory effects (different from tobacco) is essential for clinical guidance and public health messaging.

The numbers in context

Cannabis smoking associated with: bronchitis at low exposure; increased central airway resistance; lung hyperinflation; higher vital capacity; no convincing evidence of COPD, emphysema, or airflow obstruction; inconclusive evidence for lung cancer

How the study worked

Narrative review of the evidence on cannabis use disorder and respiratory health, addressing bronchitis, airflow obstruction, emphysema, lung cancer, and specific lung function patterns.

What this study cannot tell us

Narrative review. Cannabis respiratory research is limited by illegality, variable product potency, and most users also smoking tobacco. Confounding by tobacco is difficult to eliminate completely.

How to read the evidence

Comprehensive review of available evidence, limited by the inherent difficulty of isolating cannabis respiratory effects from tobacco.

When this study was published

Published in 2021.

The bigger picture

The pattern of cannabis lung effects (bronchitis without COPD, hyperinflation without obstruction) is pharmacologically unexpected and suggests cannabis smoke components may affect airways through different mechanisms than tobacco, possibly through anti-inflammatory cannabinoid effects partially counteracting smoke-induced damage.

Questions still open

Why does cannabis smoking cause bronchitis but apparently not COPD? Do the anti-inflammatory properties of cannabinoids partially protect against smoke-induced lung damage?

Common questions

Does smoking cannabis damage the lungs?

Yes, it causes bronchitis and increases airway resistance, even at relatively low exposure. However, the pattern is different from tobacco: there is no clear evidence of COPD, emphysema, or lung cancer, which are hallmarks of tobacco damage.

Why is cannabis different from tobacco for the lungs?

The reasons are not fully understood, but cannabinoids have anti-inflammatory properties that may partially counteract smoke-induced damage. The pattern of increased lung volume without obstruction is unique to cannabis and has no clear parallel in tobacco research.

Read the original research

Cannabis use disorder and the lungs.

Addiction (Abingdon, England), 116(1), 182-190

View on PubMed ↗Publisher’s paper ↗

Citation

Gracie, Kathryn; Hancox, Robert J. (2021). Cannabis use disorder and the lungs.. Addiction (Abingdon, England), 116(1), 182-190. https://doi.org/10.1111/add.15075