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Cannabis use was significantly associated with a greater risk of severe outcomes following a COVID-19 infection, according to a retrospective study that spanned the first 2 years of the pandemic.

Among more than 70,000 patients with a documented case of COVID at a large medical center in the Midwest, use of cannabis was linked with an 80% greater risk of hospitalization and a 27% higher risk for intensive care unit (ICU) admission after an infection, but no difference in all-cause mortality:

• Hospitalization: OR 1.80 (95% CI 1.68-1.93)
• ICU admission: OR 1.27 (95% CI 1.14-1.41)
• Mortality: OR 0.97 (95% CI 0.82-1.14)

The elevated risks for hospitalization and ICU admission were about on par with that of smoking, reported Li-Shiun Chen, MD, MPH, ScD, of the Washington University School of Medicine in St. Louis, and coauthors.

The electronic health record (EHR)-based study, published in , also confirmed the established link between tobacco smoking and increased risks for serious outcomes from COVID. That association was observed both in current and former smokers and included a higher risk for mortality.

"There's this sense among the public that cannabis is safe to use, that it's not as bad for your health as smoking or drinking, that it may even be good for you," Chen said in a . "I think that's because there hasn't been as much research on the health effects of cannabis as compared to tobacco or alcohol."

"What we found is that cannabis use is not harmless in the context of COVID-19," Chen continued. "People who reported yes to current cannabis use, at any frequency, were more likely to require hospitalization and intensive care than those who did not use cannabis."

Despite being more than 4 years into the pandemic, the question of cannabis use and COVID-19 severity remained unsettled. One prior study suggested that cannabis users were more likely to catch COVID and when they did, while another study found that active users had after a COVID hospitalization compared with nonusers.

In the current study, about 10% of the cohort reported cannabis use, which was defined as having answered yes to the question: "Have you used cannabis in the past year?" As a result, no details on the method of cannabis use (smoking, vaping, edibles) or frequency of use were available.

"That gave us enough information to establish that if you use cannabis, your healthcare journey will be different, but we can't know how much cannabis you have to use, or whether it makes a difference whether you smoke it or eat edibles," said coauthor Nicholas Griffith, MD, also of Washington University, in the release.

As noted, current and former tobacco smoking were both associated with increased risks for hospitalization, ICU admission, and all-cause mortality following a COVID infection:

• Hospitalization: current (OR 1.72, 95% CI 1.62-1.82) and former (OR 1.27, 95% CI 1.21-1.33)
• ICU admission: current (OR 1.22, 95% CI 1.10-1.34) and former (OR 1.25, 95% CI 1.16-1.33)
• Mortality: current (OR 1.37, 95% CI 1.20-1.57) and former (OR 1.42, 95% CI 1.30-1.55)

"The main message for the public ... is to try and reduce risk factors as much as possible," said Edward Jones-Lopez, MD, an infectious disease specialist at Keck Medicine of USC in Los Angeles, who was not involved in the research. "These two are modifiable risk factors -- meaning there is a way to stop smoking, there is a way to stop using cannabis."

Discussing the findings on smoking, Aaron Friedberg, MD, of the Ohio State Wexner Medical Center in Columbus, who also was not involved in the study, pointed out that tobacco is the biggest avoidable cause of disease and death.

"It directly damages the respiratory system and causes damage to many areas of the body such as the heart, blood vessels, brain, and other organs that can also be damaged in COVID-19," he told MedPage Today. "This could be both a case of additive damage from the combination of tobacco use and COVID-19, and also possibly increased vulnerability to severe infection from tobacco use that further increases the damage from COVID-19."

The study from Chen and colleagues included 72,501 patients identified as having COVID-19 during at least one medical visit from February 2020 to January 2022 at BJC HealthCare hospitals and clinics in Missouri and Illinois, the bulk of whom (n=40,180) were diagnosed from July 2021 onward. Of those, 70.4% were hospitalized, 6.5% were admitted to the ICU, and 3.7% died.

Patients had a mean age of 49 years (range 12 to 90), 60% were female, and 69% had at least one comorbidity. Most were white (70%) and 28% were Black. Over 70% had not been vaccinated prior to their COVID diagnosis.

Regarding substance use, 13.4% were current smokers, 24.4% former smokers, and 9.7% reported cannabis use (individuals were excluded if their smoking status was not noted in the EHR).

Analyses were adjusted for various factors, including age, sex, race/ethnicity, insurance, comorbidities, cannabis or tobacco use, date of the COVID diagnosis, and whether a dose of vaccine was received before a diagnosis.

Limitations cited by the authors included the study timeframe, that substance use data relied on patient-reported information and lacked detail on type and frequency, and that some factors such as a patient's mental health status were not included.

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