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

Q: 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.

Q: 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.

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.

Kempker, Jordan A et al.·Annals of the American Thoracic Society·2015·Moderate EvidenceCross-Sectional

Respiratory (136)Harm Reduction (776)

Quick Facts

Study Type

Cross-Sectional

Evidence

Moderate Evidence

Sample

Not reported

What This Study 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.

Key Numbers

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 They Did This

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.

Why This Research 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 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.

What This Study Doesn't 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.

Questions This Raises

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

Trust & Context

Key Stat:: Up to 20 joint-years: no adverse lung function changes
Evidence Grade:: Large population-based sample with standardized spirometry, though cross-sectional design limits causal conclusions.
Study Age:: Published in 2015 using 2007-2010 data. Cannabis potency and consumption methods have changed significantly since then.
Original Title:: The effects of marijuana exposure on expiratory airflow. A study of adults who participated in the U.S. National Health and Nutrition Examination Study.
Published In:: Annals of the American Thoracic Society, 12(2), 135-41 (2015)
Authors:: Kempker, Jordan A, Honig, Eric G, Martin, Greg S
Database ID:: RTHC-00988

Evidence Hierarchy

Meta-Analysis / Systematic Review

Randomized Controlled Trial

Cohort / Case-Control

Cross-Sectional / ObservationalSnapshot without intervening

This study

Case Report / Animal Study

A snapshot of a population at one point in time.

What do these levels mean? →

Frequently Asked 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.

Cite This Study

RTHC-00988·https://rethinkthc.com/research/RTHC-00988

APA

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

MLA

Kempker, Jordan A, et al. "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, 2015. https://doi.org/10.1513/AnnalsATS.201407-333OC

RethinkTHC

RethinkTHC Research Database. "The effects of marijuana exposure on expiratory airflow. A s..." RTHC-00988. Retrieved from https://rethinkthc.com/research/kempker-2015-the-effects-of-marijuana

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Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.

This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.

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