Cannabis use not associated with higher incidence of respiratory-related hospital visits

Cannabis use is not associated with more respiratory-related emergency department visits compared to those not using the drug, although it is associated with a higher proportion of total emergency department visits. This was the main conclusion of a propensity-matched study by a group of researchers from Ontario, Canada.

Cannabis (or marijuana) is the most commonly used addictive drug after tobacco and alcohol† The use of cannabis is associated with respiratory problems such as symptoms of chronic bronchitis and inflammation of the large airways and in fact heavy use can lead to airflow obstruction† Despite this evidence of adverse respiratory effects, a 2018 systematic review concluded that there was little evidence that cannabis smoking was associated with coughing, sputum production and wheezing and that there was insufficient evidence of a link between the use of the drug and obstructive pulmonary disease† Nevertheless, one study has suggested that: Smoking cannabis daily, even in the absence of tobacco, is associated with an increased risk of health care use for several health conditions

With some uncertainty about the respiratory effects of cannabis, in the current study the Canadian team wanted to investigate the magnitude of the association between cannabis use and adverse respiratory-related emergency room visits. They conducted a retrospective analysis that linked health research and health administrative data for Ontario residents. Individuals who self-reported cannabis use (the exposed group) in the past year were compared 1:3 (to increase the sample size) with controls, ie those who did not self-report use of the drug. The primary outcome of the study was an emergency department visit or respiratory-related hospitalization, where both upper and lower respiratory tract infections, respiratory failure, asthma, or COPD were the reason for hospitalization. As a secondary result, the team rated emergency room visits from all causes.

Cannabis use and respiratory-related hospital visits

A total of 35,114 individuals were included in the analysis, of which 6,425 with a mean age of 32.2 years (38.8% female) were self-reported cannabis users. Overall, 42.5% of those using the drug did so less than once a month, and a much smaller proportion (10.5%) reported daily use.

The odds ratio, OR = 0.91, 95% CI 0.77 – 1.09, p = 0.32) was not significantly different between the exposed and control groups. Despite this, there was a higher probability of emergency room visits for all causes among those using cannabis (OR = 1.22, 95% CI 1.13 – 1.31, p < 0.0001). The most common reason for the emergency visits among those using cannabis was for acute trauma (15.1%), although interestingly this was followed by respiratory distress (14.2%).

The authors concluded that, while there were no differences in the proportion of respiratory-related hospital visits between the two groups, all-cause hospital visits were significantly higher in those who did. self-reported cannabis use. They added that based on these findings, recreational use of the drug should be discouraged.

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Vozoris NT et al. Cannabis use and risks of respiratory and morbidity and all-cause mortality: a data-linked population-based cohort study BMJ Open Respir Res 2022

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