Study reveals cannabis and tobacco users face higher COVID-19 hospitalization and adverse outcomes

In a recent cohort study published in JAMA Network Open, researchers from the United States of America investigated the association between the use of cannabis and tobacco and health outcomes in coronavirus disease 2019 (COVID-19). They found that smokers and cannabis users showed a greater risk of hospitalization and adverse outcomes in COVID-19 as compared to non-smokers or those not using cannabis, despite controlling for other risk factors.

Study: Cannabis, Tobacco Use, and COVID-19 Outcomes. Image Credit: JOURNEY STUDIO7 / ShutterstockStudy: Cannabis, Tobacco Use, and COVID-19 Outcomes. Image Credit: JOURNEY STUDIO7 / Shutterstock


COVID-19 continues to impact public health, causing morbidity and mortality. Despite 76% of US adults being partially vaccinated against the disease, factors like vaccine hesitancy and new virus strains highlight the need to identify contributors to poor outcomes. While non-modifiable factors such as age, sex, race, and comorbidity are reported to be linked to severe infection, research on modifiable factors like substance use remains limited.

Previous studies show that cigarette smoking is associated with the worsening of COVID-19 outcomes, and preliminary evidence links substance use disorders and alcohol use to higher risks of severe disease and breakthrough infections. Research on cannabis use and COVID-19 is scarce and conflicting, with some studies indicating higher infection and mortality rates among users, while others suggest protective effects.

Data from electronic health records (EHR) may help address these understanding gaps. Therefore, researchers in the present study aimed to evaluate whether substance use, specifically cannabis use and tobacco smoking, is associated with COVID–19–related outcomes such as hospitalization, admission to the intensive care unit (ICU), and all-cause mortality. The hypothesis was that both tobacco smoking and cannabis use are linked to worse outcomes following COVID-19 infection.

About the study

In the present multi-institutional, retrospective cohort study, EHR data from 72,501 patients diagnosed with COVID-19 during the period from February 2020 to January 2022 were included. COVID-19 cases were defined by diagnosis based on the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM), positive polymerase chain reaction (PCR), antibody, or antigen tests. The mean age of the participants was 48.9 years; 59.7% of them were female, and 27.6% of the patients were Black. Approximately 26.8% of patients received a COVID-19 vaccine before diagnosis.

The primary outcomes were hospitalization, admission to the ICU, and all-cause mortality, including post-hospital mortality and overall survival. Demographic and treatment-related covariates, such as age, sex, race, ethnicity, and insurance status, were additionally extracted. Tobacco smoking and cannabis use were self-reported in the EHR, with current use documented and included in analyses. Statistical analysis included the use of chi-square tests, logistic regression, Cox proportional hazards regression, scaled Schoenfeld residuals check, and Bonferroni correction.

Results and discussion

About 70.4% of the total participants were hospitalized, 6.5% required ICU visits, and 3.7% suffered mortality. Further, 13.4% of the participants were found to be current smokers, 24.4% were former smokers, and 9.7% were current cannabis users. Both current and former smoking were found to be associated with a significantly increased risk of hospitalization, ICU admission, and all-cause mortality following COVID-19 (p<0.001), even after adjusting for various demographic and health factors. The risk of progression to all-cause mortality was found to be higher in patients above 65 years of age with current or former smoking. Current smokers also showed a higher probability of hospitalization than former smokers.

Similarly, cannabis use was found to be significantly associated with increased risks of hospitalization (OR 1.80) and ICU admission (OR 1.27) following COVID-19 but not with increased all-cause mortality. The associations between tobacco and cannabis use with COVID-19 outcomes remained consistent when adjusted for comorbidities.
While current and former smoking were found to be associated with a lower probability of receiving a COVID-19 vaccine, cannabis use did not appear to influence vaccine receipt when adjusting for variables significantly.

Further, alcohol abuse was documented in 0.3%, and vape use was recorded in 1.9% of patients, both showing a greater risk for hospitalization (OR = 3.34 and 1.20, respectively). Data limitations precluded the evaluation of their associations with COVID-19 ICU admission and mortality.

Overall, the study adds to current evidence by using extensive EHR data to identify associations between tobacco and cannabis use with increased risks of adverse COVID-19 outcomes while also exploring preliminary associations with alcohol abuse and vaping. However, the study is limited by potential confounding from time-varying factors, reliance on self-reported and variably documented substance use in EHRs, lack of details on cannabis and tobacco product use, potential detection bias, non-representativeness of the sample, and incomplete capture of patient outcomes.


In conclusion, the study suggests that current and former smoking, as well as cannabis use, increases the risk of hospitalization, ICU admission, and mortality in COVID-19 patients. The associations remain significant after adjusting for demographic and comorbidity factors, emphasizing cannabis use as an independent risk factor for adverse outcomes post-COVID-19 diagnosis. The findings highlight the need for further research on the effect of substance use on COVID-19 outcomes, especially with the increasing legalization of marijuana use.

Journal reference:
Dr. Sushama R. Chaphalkar

Written by

Dr. Sushama R. Chaphalkar

Dr. Sushama R. Chaphalkar is a senior researcher and academician based in Pune, India. She holds a PhD in Microbiology and comes with vast experience in research and education in Biotechnology. In her illustrious career spanning three decades and a half, she held prominent leadership positions in academia and industry. As the Founder-Director of a renowned Biotechnology institute, she worked extensively on high-end research projects of industrial significance, fostering a stronger bond between industry and academia.  


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