How Marijuana Smoke Affects Lung Function in U.S. Adults | Research

The takeaway

Up to 20 joint-years of marijuana use showed no adverse effect on lung function, but heavier lifetime use was linked to airflow changes driven by increased lung capacity rather than obstruction.

Read this if you smoke cannabis and wonder how it compares to cigarettes in terms of lung health.

Up to 20 joint-years: no adverse lung function changes

What the researchers found

Researchers analyzed lung function data from over 100,000 U.S. adults in the NHANES survey. Among those who had used marijuana, each additional day of use in the prior month was associated with increased forced vital capacity (FVC) but a decreased FEV1/FVC ratio.

Up to 20 joint-years of cumulative use showed no association with obstructive lung disease. Above 20 joint-years, there was a twofold increased odds of having a low FEV1/FVC ratio, but this was driven by FVC increasing rather than FEV1 decreasing.

This pattern differs from tobacco-related lung disease, where FEV1 drops disproportionately.

Why it matters

This is one of the largest population-based studies examining marijuana and lung function. The finding that heavy use changes lung volumes in a pattern distinct from tobacco-related obstruction challenges assumptions about how cannabis smoke damages airways.

The numbers in context

59.1% had used marijuana at least once; 12.2% used in past month; >20 joint-years: OR 2.1 (95% CI 1.1-3.9) for FEV1/FVC <70%; FVC increased 0.13% per additional use day (p = 0.0001)

How the study worked

Cross-sectional analysis of U.S. adults from NHANES 2007-2010 cycles. Lung function was measured by standardized spirometry. Cannabis and tobacco exposure were assessed through survey questions. Multivariable regressions adjusted for tobacco use and other confounders.

What this study cannot tell us

Cross-sectional design cannot establish causation. Self-reported marijuana use may be underestimated. The study could not account for varying potency or methods of consumption. Joint-year calculations rely on self-report accuracy.

How to read the evidence

Large population-based sample with standardized spirometry, though cross-sectional design limits causal conclusions.

When this study was published

Published in 2015 using 2007-2010 data. Cannabis potency and consumption methods have changed significantly since then.

The bigger picture

The relationship between marijuana smoke and lung health is not a simple mirror of tobacco effects. While heavy long-term use does alter lung function, the mechanism appears different from the classic obstructive pattern seen with cigarettes.

Questions still open

Why does marijuana use increase FVC? Does this FVC increase represent hyperinflation or genuine lung capacity differences? Would longitudinal follow-up show progressive changes?

Common questions

What is a joint-year?

A joint-year is a measure of cumulative marijuana exposure, similar to pack-years for cigarettes. One joint-year equals smoking one joint per day for one year.

Does this mean marijuana is safe for the lungs?

The study found no adverse effects up to 20 joint-years, but heavier use did alter lung function. The results do not prove safety, and other respiratory effects like chronic bronchitis symptoms were not the focus.

Read the original research

The effects of marijuana exposure on expiratory airflow. A study of adults who participated in the U.S. National Health and Nutrition Examination Study.

Annals of the American Thoracic Society, 12(2), 135-41

View on PubMed ↗Publisher’s paper ↗

Citation

Kempker, Jordan A; Honig, Eric G; Martin, Greg S. (2015). The effects of marijuana exposure on expiratory airflow. A study of adults who participated in the U.S. National Health and Nutrition Examination Study.. Annals of the American Thoracic Society, 12(2), 135-41. https://doi.org/10.1513/AnnalsATS.201407-333OC