Despite causing chronic bronchitis, cannabis smoking was associated with increased lung capacity rather than the decreased capacity seen with tobacco, possibly due to cannabis's bronchodilator and anti-inflammatory properties.
Read this if you smoke cannabis and want to understand how it affects your lungs compared to tobacco.
Cannabis smoking was associated with increased FVC, the opposite of tobacco's effect on lung capacity.
What the researchers found
This structured literature review found a surprising divergence between cannabis and tobacco effects on lung function. Both cause symptoms of chronic bronchitis (cough, sputum production). However, while tobacco progressively reduces forced expiratory volume (FEV1) and forced vital capacity (FVC), recent large studies showed cannabis smoking was associated with increased FVC.
The mechanism behind this paradoxical finding is unclear, but the authors suggest acute bronchodilator effects of cannabis (opening airways) and anti-inflammatory properties may play a role.
The review also noted reports of bullous lung disease (enlarged air spaces in the lungs) associated with cannabis smoking, typically in younger patients than would be expected with tobacco-related emphysema. These findings come primarily from case reports and small series.
Why it matters
As cannabis use increases, understanding its respiratory effects is important for both individual health decisions and public health guidance. The finding that cannabis may not cause the same progressive lung function decline as tobacco challenges assumptions about inhaling any combusted plant material.
The numbers in context
Cannabis smoking was associated with increased FVC in large population studies. Bullous lung disease has been reported in cannabis smokers at younger ages than typical for tobacco-related emphysema.
How the study worked
Structured literature review examining published studies on the effects of cannabis smoking on lung function and respiratory symptoms. The review considered both large population-based studies and case reports, addressing the challenge of confounding from concurrent tobacco use.
What this study cannot tell us
Long-term cannabis-only smoking studies are rare because most cannabis smokers also use tobacco. The review notes this confounding factor as a major limitation across the literature. Case reports of bullous lung disease cannot establish how common this condition is among cannabis smokers.
How to read the evidence
Moderate evidence from a structured review of multiple studies, including large population-based analyses. The counterintuitive findings are consistent across studies but mechanisms are not fully explained.
When this study was published
Published in 2016. Subsequent large studies have continued to show divergent effects of cannabis and tobacco on lung function.
The bigger picture
The respiratory effects of cannabis smoking represent one of the most counterintuitive findings in cannabis research. While common sense suggests that inhaling any smoke damages the lungs similarly, the pharmacological properties of cannabinoids appear to modify the expected damage pattern. This does not mean cannabis smoking is safe for the lungs, but it suggests the harm profile is different from tobacco.
Questions still open
- What is the mechanism by which cannabis increases rather than decreases FVC? Do the bronchodilator effects of THC fully explain the lung function findings? Would long-term cannabis-only smoking (without tobacco) show different respiratory outcomes? Is vaporization meaningfully safer than smoking for respiratory health?
Common questions
Does smoking cannabis damage your lungs?
Why would cannabis increase lung capacity?
Read the original research
Effect of cannabis smoking on lung function and respiratory symptoms: a structured literature review.
NPJ primary care respiratory medicine, 26, 16071
Citation
Ribeiro, Luis Ig; Ind, Philip W. (2016). Effect of cannabis smoking on lung function and respiratory symptoms: a structured literature review.. NPJ primary care respiratory medicine, 26, 16071. https://doi.org/10.1038/npjpcrm.2016.71
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