Cannabis use significantly increases the risk of severe COVID-19, according to a study that found cannabis users are more likely to require hospital admission and intensive care if they become infected with the coronavirus.
Since COVID-19 began to spread, scientists have been investigating to determine which people were at higher risk of developing severe symptoms of the disease. They soon identified certain characteristics, such as older age, a history of smoking, a high body mass index (BMI), and the presence of other diseases such as diabetes, which made people infected with SARS-CoV-2 much more likely to become seriously ill, and even die.
However, one suggested risk factor remains unconfirmed more than four years into the pandemic: cannabis use, with evidence emerging suggesting both protective and harmful effects. Now, a new study by researchers at Washington University School of Medicine in St. Louis points decisively to the latter: cannabis is linked to an increased risk of severe illness for people who contract COVID-19.
Researchers came to this conclusion after analyzing the health records of 72,501 people treated for COVID-19 at health centers in a major Midwestern U.S. health care system during the first two years of the pandemic and finding that people who reported using any form of cannabis at least once in the year before developing COVID-19 were significantly more likely to require hospitalization and intensive care compared with people without such a history. This elevated risk of severe disease was comparable to that of smoking.
“There is a perception 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,” said Dr. Li-Shiun Chen, professor of psychiatry and senior author. “I think that’s because there hasn’t been as much research on the health effects of cannabis compared to tobacco or alcohol. What we found is that cannabis use is not harmless in the context of COVID-19. People who reported current cannabis use, at any frequency, were more likely to require hospitalization and intensive care than those who did not use cannabis.”
Cannabis use was different from smoking on one key outcome measure: survival. While smokers were significantly more likely to die from COVID-19 than nonsmokers — a finding consistent with numerous other studies — the same was not true for cannabis users, according to the study, which has been published in JAMA Network Open. “The independent effect of cannabis is similar to the independent effect of tobacco with respect to the risk of hospitalization and intensive care,” Chen said. “For the risk of death, the risk of tobacco is clear, but more evidence is needed for cannabis.”
Cannabis users are more likely to be hospitalized for COVID
The study analyzed de-identified electronic health records of people cared for for COVID-19 at BJC HealthCare hospitals and clinics in Missouri and Illinois between Feb. 1, 2020, and Jan. 31, 2022. The records contained data on demographic characteristics such as sex, age, and race; other medical conditions such as diabetes and heart disease; substance use including tobacco, alcohol, cannabis, and vaping; and disease outcomes—specifically, hospitalization, intensive care unit (ICU) admission, and survival.
COVID-19 patients who reported using cannabis in the past year were 80% more likely to be hospitalized and 27% more likely to be admitted to the ICU than patients who had not used cannabis, after accounting for smoking, vaccination, other health conditions, date of diagnosis, and demographic factors. In comparison, tobacco smokers with COVID-19 were 72% more likely to be hospitalized and 22% more likely to require intensive care than nonsmokers, after adjusting for other factors.
Cannabis, which is known to suppress the immune system, may undermine the body’s ability to fight off viral infections no matter how it is consumed.
These results contradict some other research suggesting cannabis can help the body fight off viral diseases like COVID-19. “Most of the evidence suggesting cannabis is good for you comes from cell or animal studies,” Chen said. “The advantage of our study is that it is in people and uses real-world healthcare data collected at multiple sites over a long period. All outcomes were verified: hospitalization, ICU stay, death. Using this dataset, we were able to confirm the well-established effects of smoking, suggesting the data is reliable.”
The study was not designed to answer why cannabis use might make COVID-19 worse. One possibility is that inhaling marijuana smoke injures delicate lung tissue and makes it more vulnerable to infection, much the same way tobacco smoke causes lung damage that puts people at risk for pneumonia, the researchers said. This doesn’t mean taking edibles is safer than smoking joints. It’s also possible that cannabis, known to suppress the immune system, undermines the body’s ability to fight off viral infections no matter how it’s consumed, the researchers noted.
“We don’t know if edibles are safer,” said first author Dr. Nicholas Griffith, a medical resident at Washington University who was a medical student at Washington University when he led the study. “People were asked a yes-or-no question: ‘Have you used cannabis in the past year?’ That gave us enough information to establish that if you use cannabis your health care journey will be different, but we can’t know how much cannabis you have to use, or if there’s a difference between smoking it or consuming it in edible form. Those are questions we’d really like to find answers to. I hope this study opens the door to more research on the health effects of cannabis.”
