Cannabis smoking causes airway inflammation and bronchitis but surprisingly limited evidence for COPD or emphysema | Research

The takeaway

A review found consistent evidence that cannabis smoking causes large airway inflammation and bronchitis, but unconvincing evidence for COPD-like airflow obstruction, with inconclusive evidence for lung cancer.

Read this if you smoke cannabis and want to understand the actual evidence about lung health effects.

Cannabis has quite different lung effects than tobacco despite being smoked

What the researchers found

The review noted that despite cannabis being the most widely used illicit drug, respiratory effects were surprisingly under-researched. Key findings:

Consistent evidence showed cannabis smoking was associated with large airway inflammation, bronchitis symptoms, increased airway resistance, and lung hyperinflation.

However, the evidence that cannabis leads to COPD features (airflow obstruction and emphysema) was "not convincing." While case reports described bullous emphysema in cannabis smokers, systematic studies had not confirmed this association. These cases likely represented uncommon adverse effects in very heavy users.

The assumption that cannabis smoking would have similar effects to tobacco smoking appeared to be incorrect. Cannabis had quite different effects on lung function.

Evidence for respiratory malignancies was described as "controversial" and "inconclusive."

Why it matters

The finding that cannabis and tobacco have different lung effects challenged assumptions and had implications for harm reduction messaging and clinical assessment of cannabis smokers.

The numbers in context

Consistent findings: large airway inflammation, bronchitis symptoms, increased airway resistance, lung hyperinflation. Not convincing: COPD-like obstruction, emphysema. Inconclusive: lung cancer.

How the study worked

Expert review of observational studies examining the effects of cannabis smoking on respiratory function, including studies of lung function parameters, airway inflammation, and cancer risk.

What this study cannot tell us

Inherent difficulty studying an illegal habit. Confounding by concurrent tobacco use in many studies. Limited long-term prospective data. Publication bias toward positive findings.

How to read the evidence

Expert review synthesizing available evidence with honest assessment of what was convincing versus inconclusive.

When this study was published

Published in 2011. Larger longitudinal studies have since provided more data on cannabis and lung function.

The bigger picture

This review helped distinguish cannabis lung effects from tobacco effects, establishing that while cannabis smoking is not harmless to the lungs, it may not carry the same specific risks as tobacco for chronic lung disease.

Questions still open

Why does cannabis affect the lungs differently than tobacco? Would vaporization or oral consumption avoid the respiratory effects of smoked cannabis?

Common questions

Does smoking cannabis cause the same lung damage as tobacco?

This review found that cannabis and tobacco have different lung effects. Cannabis consistently caused airway inflammation and bronchitis but the evidence for COPD-like damage was not convincing, unlike tobacco.

Can smoking cannabis cause lung cancer?

The evidence at the time was described as "controversial" and "inconclusive." There was some evidence cannabis could be an occasional cause, but it was difficult to separate from the effects of concurrent tobacco smoking.

Read the original research

Effects of smoking cannabis on lung function.

Expert review of respiratory medicine, 5(4), 537-46; quiz 547

View on PubMed ↗Publisher’s paper ↗

Citation

Lee, Marcus H S; Hancox, Robert J. (2011). Effects of smoking cannabis on lung function.. Expert review of respiratory medicine, 5(4), 537-46; quiz 547. https://doi.org/10.1586/ers.11.40