High before the low: Cannabis increases risk of severe COVID-19 - study

Partaking in cannabis, a recreational and medicinal substance commonly smoked or ingested, may increase the risk of severe COVID-19, a new study published on Friday found. 

The research, published in the peer-reviewed academic journal JAMA Network, found that one of the many factors increasing the risk of a severe COVID infection is smoking cannabis. 

While early research found that factors such as BMI, smoking history, age and pre-existing conditions could also impact the severity of the infection, it is only now that the relationship between cannabis and COVID has been established. 

Researchers at the Washington University School of Medicine in St. Louis analyzed the health records of 72,501 people who saw a medical professional for COVID-19. The data was sources from  BJC HealthCare hospitals and clinics in Missouri and Illinois between Feb. 1, 2020, and Jan. 31, 2022.

Through analyzing the data, the researchers established a pattern that those who had used any form of cannabis in the year prior to contracting the virus were significantly more likely to be hospitalized or put in intensive care compared to those who had not partaken. 

“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,” said senior author Li-Shiun Chen, MD, DSc, a professor of psychiatry. “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. 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.”

Is all smoking equally bad?

While using cannabis was linked to increased risk of hospitalization, smoking tobacco increased the risk of a more deadly outcome with a COVID diagnosis. Those who smoked tobacco were more likely to die from the virus compared to cannabis users and people who did not smoke.

“The independent effect of cannabis is similar to the independent effect of tobacco regarding the risk of hospitalization and intensive care,” Chen said. “For the risk of death, tobacco risk is clear but more evidence is needed for cannabis.”

Patients who had admitted to using cannabis in the year prior to contracting COVID were 80% more likely to be hospitalized and 27% more likely to be admitted to the ICU than patients who had not used cannabis. 

Patients who smoked tobacco 9 were 72% more likely to be hospitalized and 22% more likely to require intensive care than were nonsmokers with COVID-19.

“Most of the evidence suggesting that cannabis is good for you comes from studies in cells or animals,” Chen said. “The advantage of our study is that it is in people and uses real-world health-care data collected across multiple sites over an extended time period. All the outcomes were verified: hospitalization, ICU stay, death. Using this data set, we were able to confirm the well-established effects of smoking, which suggests that the data are reliable.”

Why might cannabis be worsening COVID infections?

The researchers expressed that it was possible that inhaling cannabis smoke injures lung tissue and the damaged tissue would therefore be made more vulnerable to infection. 

However, the researchers insisted that ingesting cannabis may still carry risk as they said it could suppress the body’s immune system and inhibit its ability to fight the virus. 

“We just don’t know whether edibles are safer,” said first author Nicholas Griffith, MD, a medical resident at Washington University. Griffith 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 whether it makes a difference whether you smoke it or eat edibles. Those are questions we’d really like the answers to. I hope this study opens the door to more research on the health effects of cannabis.”