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Cannabis use disorder may increase risk of COVID-19 hospitalization



Cannabis use disorder may increase risk of COVID-19 hospitalization

Researchers in the United States have conducted a study suggesting that genetic vulnerability to a psychiatric syndrome called cannabis use disorder (CUD) may increase the risk of developing severe coronavirus disease 2019 (COVID-19) that requires hospitalization.

Cannabis use disorder (CUD) is a moderately-heritable psychiatric syndrome that is genetically correlated with respiratory disease, says the team.

Using genome-wide associated analysis (GWAS) summary statistics, the researchers identified a partial genetic overlap between vulnerability to CUD and susceptibility to COVID-19 that requires hospitalization.

Further analysis revealed a genomic association between CUD and COVID-19 hospitalization that remained after accounting for potential confounders such as age, smoking status, cardiometabolic traits, and indicators of socioeconomic status.

“Heavy problematic cannabis use may increase chances of hospitalization due to COVID-19 respiratory complications,” write the researchers.

The team – from Washington University in St. Louis and the University of Colorado – says, “curbing excessive cannabis use may be an essential strategy in COVID-19 mitigation.”

A pre-print version of the paper is available on the medRxiv* server, while the article undergoes peer review.


Risk of COVID-19 hospitalization could be linked to behavioral factors

Genetic vulnerability to hospitalization following infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) – the agent that causes COVID-19 – could be partially linked to comorbid behavioral risk factors, particularly the use of combustible psychoactive substances, say Alexander Hatoum (Washington University School of Medicine) and colleagues.

Reports have shown that over the course of the COVID-19 pandemic, laws that would usually prohibit the use of cannabis have increasingly permitted its recreational use.

On November 3rd, 2020, people in Arizona, Montana, New Jersey, and South Dakota voted to join eleven other states that have already legalized the recreational use of cannabis.

Research has also shown that legalization is associated with the increased use of the substance and that one-fifth of people who have tried cannabis go on to develop cannabis CUD.

Hatoum and team say it has already been demonstrated that CUD is moderately heritable (50-60%) and genetically correlated with the risk of developing respiratory disease.

“As the heterogeneous presentation of COVID-19 is partially attributable to host genomic background and respiratory symptoms are the primary reason for hospitalization and death, genomic liability to CUD may contribute to severe COVID-19 presentation,” write the researchers.

What did the current study involve?

The team used GWAS summary statistics on CUD (14,080 cases; 343,726 controls) and COVID-19 hospitalization (6,492 cases; 1,012,809 population controls) to assess whether genetic susceptibility to CUD could plausibly influence the risk of being hospitalized with COVID-19.

Using linkage disequilibrium score regression analyses, the researchers found that at least one-third of genetic vulnerability to COVID-19 hospitalization overlapped with genetic susceptibility to CUD.

“Genetic causality as a potential mechanism of risk could not be excluded,” say Hatoum and the team.

Using a series of genomic structural equation models, the researchers identified an independent genomic association between CUD and COVID-19 hospitalization, following adjustment for a range of potential confounders.

These variables included genomic susceptibility to tobacco phenotypes (e.g., cigarettes smoked per day, lifetime cannabis use and smoking cessation); cardiometabolic factors (BMI and fasting glucose); socioeconomic status (educational attainment, Townsend deprivation index) and forced expiratory volume.

In addition, latent causal variable analyses provided evidence to support that susceptibility to CUD could be genetically causal for COVID-19 hospitalization.

Highly speculative, but plausible, says the team

The researchers acknowledge that the use of population controls (individuals who may or may not have had COVID-19) in the GWAS may have impacted the precision of the association estimate.

They also acknowledge that the GWAS statistics were mainly generated from samples of genomically-confirmed European ancestry, which may limit the generalizability of the findings to other ancestral populations.

Hatoum and colleagues say that, while highly speculative, it is plausible that heavy and problematic cannabis use associated with CUD could increase the risk of severe COVID-19.

“As the world prepares for surges in COVID-19, identifying putative risk factors associated with severe presentations may mitigate its worldwide impact,” say the researchers.

“In contrast to anecdotal evidence and media reports that cannabis may attenuate COVID-19, these data urge caution in heavy cannabis use during the COVID-19 pandemic,” they conclude.







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Kathryn Gracie et al. Addiction. 2020

Cannabis use disorder and the lungs


Cannabis is one of the world's most widely used recreational drugs and the second most commonly smoked substance. Research on cannabis and the lungs has been limited by its illegal status, the variability in strength and size of cannabis cigarettes (joints), and the fact that most cannabis users also smoke tobacco, making the effects difficult to separate. Despite these difficulties, the available evidence indicates that smoking cannabis causes bronchitis and is associated with changes in lung function. The pattern of effects is surprisingly different from that of tobacco. Whereas smoking cannabis appears to increase the risk of severe bronchitis at quite low exposure, there is no convincing evidence that this leads to chronic obstructive pulmonary disease. Instead, cannabis use is associated with increased central airway resistance, lung hyperinflation and higher vital capacity with little evidence of airflow obstruction or impairment of gas transfer. There are numerous reports of severe bullous lung disease and pneumothorax among heavy cannabis users, but convincing epidemiological data of an increased risk of emphysema or alveolar destruction are lacking. An association between cannabis and lung cancer remains unproven, with studies providing conflicting findings


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Study: Cannabis Inhalation Not Associated With COPD, Other Tobacco-Related Harms




London, United Kingdom: Cannabis smoke exposure, even long-term, is not positively associated with chronic obstructive pulmonary disease (COPD), lung cancer, or irreversible airway damage, according to a literature review published in the journal Breathe.


British researchers reviewed nearly 20 observational studies assessing cannabis inhalation and lung health, involving over 25,000 subjects.


Investigators reported that the available literature fails to support an association between cannabis smoke exposure and the onset of COPD, emphysema, lung cancer, shortness of breath, or irreversible airway damage.


“The long-term respiratory effects of cannabis differ from traditional smoking,” authors concluded. “[C]annabis smoking does not appear to be carcinogenic.”

Researchers did identify a link between marijuana inhalation and more frequent cough, sputum production, wheezing, and chronic bronchitis – though they acknowledged that these symptoms largely cease upon quitting. Authors also acknowledged that vaporizing cannabis – a process which activates cannabinoids, but does not heat them to the point of combustion – reduces many of these symptoms.

The study’s findings are similar to those of others reporting that cannabis smoke and tobacco smoke differ significantly in their health effects, and that long-term marijuana smoke exposure is not associated with poor lung health


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Study: Marijuana Smoking Not Associated With Airway Cancers, COPD, Emphysema, Or Other Tobacco-Related Pulmonary Complications


Pulmonary complications associated with the regular smoking of cannabis are “relatively small” and far lower than those associated with tobacco smoking, according to a recent review published in the June edition of the scientific journal Annals of the American Thoracic Society. 


The paper – authored by Donald P. Tashkin, MD, emeritus professor of medicine and medical director of the Pulmonary Function Laboratory at the David Geffen School of Medicine at University of California, Los Angeles – is “the most comprehensive and authoritative review of the subject ever published,” according to an accompanying commentary.


Donald Tashkin conducted US-government sponsored studies of marijuana and lung function for over 30 years. 


His review finds that although smoking cannabis may be associated with symptoms of chronic bronchitis, studies do not substantiate claims that it is positively associated with the development of lung cancer, chronic obstructive pulmonary disease (COPD), emphysema, or bullous lung disease.


“[H]abitual use of marijuana alone does not appear to lead to significant abnormalities in lung function,”


Tashkin writes. “[F]indings from a limited number of well-designed epidemiological studies do not suggest an increased risk of either lung or upper airway cancer from light or moderate use. … Overall, the risks of pulmonary complications of regular use of marijuana appear to be relatively small and far lower than those of tobacco smoking.”


Writing in an accompanying commentary, McGill University’s Dr. Mark Ware concludes: “Cannabis smoking is not equivalent to tobacco smoking in terms of respiratory risk. … [C]annabis smoking does not seem to increase risk of chronic obstructive pulmonary disease (COPD) or airway cancers.


In fact, there is even a suggestion that at low doses cannabis may be protective for both conditions. … This conclusion will affect the way health professionals interact with patients, parents with teenagers, and policy makers with their constituents. …


Efforts to develop cleaner cannabinoid delivery systems can and should continue, but at least for now, [those] who smoke small amounts of cannabis for medical or recreational purposes can breathe a little bit easier..



Edited by twigs
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