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New Study Clears the Air: Cannabis May Not Hike Respiratory Risks, But the Road to ER Visits Gets Stonier

Written by Andrew Le, MD

UpdatedMarch 7, 2024

Cannabis, better known to many as marijuana, has become one of the most widely used psychoactive substances globally. Its reputation has seen dramatic shifts from a strictly controlled drug to a legally accessible relaxation and medicinal agent in various regions of the world, including parts of Canada and the United States. Despite its increasing societal acceptance and legalization, important questions about its safety linger. This has spurred researchers to dive deep into its effects—particularly concerning lung health, given that smoking is a common method of consumption.

An illuminating new study titled "Cannabis use and risks of respiratory and all-cause morbidity and mortality: a population-based data-linkage cohort study", published in the BMJ Open Respiratory Research journal, attempts to clarify the relationship between cannabis use and respiratory health. The research, conducted in Ontario, Canada, scrutinized the health data of residents aged 12 to 65 between January 2009 and December 2015. It provides insights that are crucial not only for users but also for healthcare professionals, policymakers, and the broader public to ponder.

Let's dissect the findings and implications of this cutting-edge study, condensing its meticulous details into digestible information for everyone.

Background and Methods

The researchers centered their investigation on a retrospective cohort study—a type of research design that observes outcomes in groups of subjects over time. They linked survey data, documenting health behaviors like cannabis use, with health administrative information to track emergency room (ER) visits, hospitalizations, and even mortality down the line.

Participants who had reported using cannabis in the past year were matched with control individuals—people who had either never used cannabis or had only used it once over a year ago. This matching was done using a method called propensity score matching, which essentially helps equate groups based on several variables, thus minimizing potential biases and allowing for a fair comparison. In this study, the matching was done on an impressive 31 different variables.

The results focused chiefly on occurrences related to the respiratory system, all-cause ER visits or hospitalizations, and death from any cause within 12 months following their designated index date—the date from which the observations were made.

Key Findings

After diligent data sifting, the study encompassed an impressive 35,114 individuals, with 6,425 identified as cannabis users within the prior year. Remarkably, among this subset, the researchers were able to match 4807 cannabis users with 10,395 controls using the intricate propensity score method.

The propensity score-matched analysis revealed some striking results. First and foremost, contrary to what some might assume due to the irritative properties of smoke, there was no significant difference in the likelihood of respiratory-related ER visits or hospitalizations when comparing cannabis users to non-users. The odds ratio—a measure of association between an exposure and an outcome—stood at 0.91. This suggests that cannabis users were not more likely to end up in the ER or be hospitalized for respiratory issues than their counterparts who didn't use cannabis.

However, not all the news was tranquilizing. Cannabis users were found to have a significantly higher likelihood of all-cause ER visits or hospitalizations, with an odds ratio of 1.22. Respiratory-related reasons, surprisingly, were second only to other causes leading to these all-cause medical visits and hospitalizations among cannabis users. Despite these concerning all-cause medical interactions, no significant difference was noted regarding all-cause mortality between users and non-users.

The researchers were careful to point out that although cannabis smoking shares similarities with tobacco smoking—containing alike volatile compounds and damaging constituents—its relationship with airways health is a contentious topic. Cannabis smoking has indeed been associated with symptoms like chronic coughs, increased sputum production, and wheezing, and even causes inflammation of the airways similar to tobacco smokers upon closer examination with tools like bronchoscopy.

Cannabis smoking's potential to cause acute respiratory illness arises through several mechanisms. Cannabis destroys certain cells lining the airways that are essential for clearing mucus, and it may potentially suppress the immune system, making infections more likely. Also, since cannabis products often contain microorganisms and can lead to vomiting, users could be at risk for developing respiratory infections from these various angles.

However, evidence from this study does not support a clear link between cannabis use and acute respiratory complications requiring ER visits or hospitalizations. Still, it cannot be ignored that users had a higher rate of all-cause medical interactions, signaling that recreational cannabis use is anything but benign.

Implications for the Future

The study’s implications are significant and multifaceted. For research, it invites further investigations that might explore longer-term impacts, different age brackets, or dive into the various ways cannabis can be consumed. For healthcare practice, it suggests vigilance in monitoring cannabis users for potential health issues beyond just respiratory concerns. And for policy, it gestures towards a need for a more nuanced approach to cannabis regulation and public health messaging—emphasizing that legal doesn’t always equate to harmless.

In conclusion, while this research draws a more detailed map of how cannabis use relates to health risks, it also charts out a myriad of new questions and avenues to consider. With cannabis use on the rise, ongoing research like this is crucial for making informed decisions that prioritize public health.


Vozoris NT, Zhu J, Ryan CM, et alCannabis use and risks of respiratory and all-cause morbidity and mortality: a population-based, data-linkage, cohort studyBMJ Open Respiratory Research 2022;9:e001216. doi: 10.1136/bmjresp-2022-001216