Letter Cautions Survey Links Between Cannabis, Asthma and COPD

A methodological letter published in the Journal of General Internal Medicine argues that reported associations between recent inhaled cannabis use, asthma and chronic obstructive pulmonary disease (COPD) in a population-based cross-sectional survey require cautious interpretation. The letter, written by Donald P. Tashkin, concerns an analysis of 379,049 respondents to the Behavioral Risk Factor Surveillance System (BRFSS), a telephone survey.

He praises the investigators for restricting their analysis to lifetime nonsmokers of tobacco while identifying two central weaknesses: chronic bronchitis was included in the definition of COPD, and asthma was not necessarily confirmed through objective testing. Restricting the study population to people who had never smoked tobacco was, in Tashkin’s view, an important design choice. Tobacco is a major risk factor for COPD and an important contributor to asthma morbidity, so including people with a history of tobacco use would have complicated efforts to distinguish a possible cannabis association from the effects of concomitant smoking.

The letter also notes that the investigators included very large numbers of recent cannabis users in the BRFSS survey. This restriction addressed one important source of confounding, but it did not resolve the problems created by how respiratory conditions were identified in the available data. The first concern involves the study’s definition of COPD.

Chronic bronchitis is not synonymous with COPD, the letter states, because COPD requires objective confirmation of airflow obstruction that is not fully reversible. The relevant spirometric criterion is a post-bronchodilator ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC) below 0.70. By contrast, chronic bronchitis is identified by symptoms such as chronic cough and sputum.

Those symptoms are common among cannabis smokers who do not have COPD. Including chronic bronchitis within the study’s COPD definition could therefore produce an apparent association between cannabis use and COPD even among people who do not have objectively confirmed airflow obstruction. A similar issue applies to the asthma analysis.

The letter observes that asthma is often diagnosed on the basis of symptoms, including frequent wheezing and cough, without objective confirmation through spirometric evidence of reversible bronchospasm or evidence of bronchospasm provoked by bronchial challenge. If the survey-based classification cannot distinguish cannabis-associated respiratory symptoms from symptoms used to diagnose asthma, the reported association between cannabis use and asthma may partly reflect symptom overlap rather than confirmed disease. The absence of self-reported spirometry findings in the BRFSS telephone survey is therefore relevant to how both findings should be understood.

This critique does not establish that inhaled cannabis has no relationship to asthma or COPD, nor does the letter report new clinical outcomes. Instead, it focuses on measurement in a cross-sectional survey of self-reported information. The source study was large and its restriction to lifetime tobacco nonsmokers strengthened its attempt to address tobacco-related confounding, but the inclusion of chronic bronchitis in the COPD definition and the reliance on symptoms without objective respiratory testing limit the conclusions that can be drawn.

The letter’s central position is that the survey’s reported associations should not be treated as equivalent to diagnoses confirmed by physiological testing. A respondent with cough, sputum or wheezing may report symptoms that resemble chronic bronchitis or asthma without meeting the accepted clinical criteria for either condition, making cautious interpretation essential to the study’s scientific meaning.

Subject of Research: Interpretation of survey associations among inhaled cannabis users, asthma and COPD

Article Title: Inhaled Cannabis, Asthma, and Chronic Obstructive Pulmonary Disease: a Population-Based Cross-Sectional Study of n = 379,049: Letter to the Editor

Article References: Tashkin, D. P. (2026). Inhaled Cannabis, Asthma, and Chronic Obstructive Pulmonary Disease: a Population-Based Cross-Sectional Study of n = 379,049: Letter to the Editor. Journal of General Internal Medicine. https://doi.org/10.1007/s11606-026-10745-4

Image Credits: AI Generated

DOI: 10.1007/s11606-026-10745-4

Keywords: inhaled cannabis, asthma, COPD, chronic bronchitis, respiratory symptoms, airflow obstruction, spirometry, BRFSS, cross-sectional study, research methods, Inhaled, Cannabis