Cannabis is the most commonly used psychoactive drug worldwide and its use is rising but data published on the association between cannabis smoking and airways health have been contradictory.
Prevalent past-year use rate in the Canadian population in 2021 was estimated to be 25%. Although cannabis can be consumed in a variety of ways, smoking combusted cannabis is the most predominant route in that country.
While cannabis contains similar types and quantities of volatile compounds (e.g. ammonia, hydrocyanic acid, etc.) and tar components (e.g. phenols, naphthalene, etc.) as tobacco, (which are implicated in the development of tobacco smoking-related airway disease), data published on the association between cannabis smoking and airways health have been contradictory.
On the one hand, cannabis smoking has been shown to be associated with the development of chronic bronchitis-type symptoms (including chronic cough, chronic sputum production and wheezing), and similar changes of bronchial inflammation are evident on bronchoscopy and endobronchial biopsies among cannabis and tobacco smokers.
On the other, it has largely thus far not been found to be associated with pulmonary function test measures of airflow obstruction, such as declining forced expiratory volume in one second (FEV1) or reduced FEV1/forced vital capacity ratio as a result of a low FEV1 (with a few recently published exceptions), or with thoracic CT evidence of emphysema.
Cannabis smoking might theoretically predispose to acute respiratory illness in several ways: it is known to destroy airway ciliated columnar epithelial cells and promote mucous-secreting goblet cell hyperplasia and such changes may predispose to acute respiratory tract infection; δ-9 tetrahydrocannabinol has potential immunosuppressive effects, which may contribute to acute respiratory tract infection; cannabis is frequently contaminated with pathogenic micro-organisms; and, cannabis use can contribute to altered mental state and/or hyperemesis, which might then lead to an aspiration event.
There is scarce data on the association between cannabis smoking and acute respiratory illness. Compared with non-cannabis smokers, one small study reported significantly higher frequency of protracted acute bronchitis episodes, and another study a significantly greater number of outpatient visits for respiratory illness (but not hospitalisations), among cannabis smokers.
Using linked health survey and health administrative data, our purpose was to evaluate the association between cannabis use and more serious, acute, adverse respiratory events, as identified by emergency room (ER) presentation or hospital admission for respiratory-related reasons.
What this study adds
Our population-based, retrospective, propensity score matched cohort study, involving 15,202 individuals and extensive covariate adjustment, showed no significant difference in the frequency of respiratory-related emergency room visits or hospitalisations between cannabis users (3.6%) and never-users (3.9%), but all-cause emergency room visits or hospitalisations were significantly greater among cannabis users (30.0% vs 26.0%).
Respiratory-related reasons were the second leading aetiology for all-cause ER visits and hospitalisations among cannabis users.
How this study might affect research/policy
Given that all-cause emergency visits or hospitalisations, which are a clinically important morbidity marker, were significantly greater among cannabis users than among control individuals, and respiratory-related reasons were the second most common cause for emergency visits and hospitalisations in the all-cause outcome, our results suggest that the worldwide rising use of recreational cannabis needs to be curtailed.
Study details
Cannabis use and risks of respiratory and all-cause morbidity and mortality: a population-based, data-linkage, cohort study
Nicholas T Vozoris, Jingqin Zhu, Clodagh M Ryan, Chung-Wai Chow and Teresa To.
Published in BMJ Open Respiratory Research in Volume 9, June 2022
Abstract
Introduction
Although cannabis is frequently used worldwide, its impact on respiratory health is characterised by controversy.
Objective
To evaluate the association between cannabis use and respiratory-related emergency room (ER) visits and hospitalisations.
Methods
A retrospective, population-based, cohort study was carried out, linking health survey and health administrative data for residents of Ontario, Canada, aged 12–65 years, between January 2009 and December 2015. Individuals self-reporting cannabis use within the past year were matched to control individuals (people who reported never using cannabis, or used cannabis only once, and more than 12 months ago) in upwards of a 1:3 ratio on 31 different variables, using propensity score matching methods. Respiratory-related and all-cause ER visits or hospitalisations, and all-cause mortality, were evaluated up to 12 months following the index date.
Results
We identified 35,114 individuals who had either used cannabis in the past year or were controls, of whom 6,425 (18.3%) used cannabis in the past year. From this group, 4,807 (74.8%) were propensity-score matched to 10,395 control individuals. In the propensity score matched cohort, there was no significant difference in odds of respiratory-related ER visit or hospitalisation between cannabis users and the control group (OR 0.91, 95% CI 0.77 to 1.09). Compared with control individuals, cannabis users had significantly increased odds of all-cause ER visit or hospitalisation (OR 1.22, 95% CI 1.13 to 1.31) and there was no significant difference with respect to all-cause mortality (OR 0.99, 95% CI 0.49 to 2.02).
Conclusions
Although no significant association was observed between cannabis use and respiratory-related ER visits or hospitalisations, the risk of an equally important morbidity outcome, all-cause ER visit or hospitalisation, was significantly greater among cannabis users than among control individuals. Therefore, cannabis use is associated with increased risk for serious adverse health events and its recreational consumption is not benign.
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