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Cannabis use linked to elevated risk of severe COVID-19

As COVID-19 began its global spread in late 2019, scientists raced to identify who was most at risk. Cannabis use and its potential effects on Covid infection remained unclear.

Factors such as age, smoking history, high body mass index (BMI), and pre-existing conditions like diabetes were quickly recognized as increasing the likelihood of severe illness and death. However, evidence on cannabis’s protective or harmful effects was conflicting.

Recent research has now provided more definitive answers. A study published by researchers at Washington University School of Medicine in St. Louis has established that cannabis use is associated with a higher risk of severe COVID-19 illness.

Cannabis use and COVID-19

The experts analyzed the health records of 72,501 individuals treated for COVID-19 at health centers in a major Midwestern health-care system during the first two years of the pandemic.

The researchers discovered that individuals who reported using cannabis at least once in the year before contracting COVID-19 were significantly more likely to require hospitalization and intensive care compared to non-users. This elevated risk was comparable to that posed by tobacco smoking.

“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 Dr. Li-Shiun Chen, a professor of psychiatry and the senior author of the study.

“Our research shows that cannabis use is not harmless in the context of COVID-19. People who reported any cannabis use were more likely to require hospitalization and intensive care than those who did not use cannabis.”

Unlike tobacco smokers, who had a significantly higher mortality rate from COVID-19, cannabis users did not exhibit a similarly increased risk of death.

Elevated COVID-19 risks for cannabis users

The study utilized deidentified electronic health records from BJC HealthCare hospitals and clinics in Missouri and Illinois, covering the period from February 1, 2020, to January 31, 2022.

These records included data on demographics, medical conditions, substance use, and COVID-19 outcomes such as hospitalization, ICU admission, and survival.

The findings revealed that COVID-19 patients who used cannabis in the previous year were 80% more likely to be hospitalized and 27% more likely to be admitted to the ICU compared to non-users.

In contrast, tobacco smokers were 72% more likely to be hospitalized and 22% more likely to require intensive care than non-smokers.

Many questions remain unanswered

“These results challenge some research suggesting that cannabis may help the body fight off viral diseases like COVID-19,” noted Dr. Chen.

“Most of the evidence supporting the benefits of cannabis comes from studies in cells or animals. Our study’s strength lies in its use of real-world health-care data over an extended period, allowing us to verify outcomes like hospitalization and ICU stay.”

The study did not determine why cannabis use might exacerbate COVID-19. One theory is that inhaling marijuana smoke damages lung tissue, making it more susceptible to infection, similar to tobacco smoke.

Another possibility is that cannabis, known to suppress the immune system, hinders the body’s ability to combat viral infections, regardless of consumption method.

“We don’t know whether edibles are safer,” added Dr. Nicholas Griffith, the study’s first author and a medical resident at Washington University.

“Our data showed that any cannabis use in the past year affected health outcomes, but we couldn’t determine the impact of different consumption methods or amounts. We hope this study encourages further research on cannabis’s health effects.”

While public perception may deem cannabis as relatively safe, this study highlights its potential risks in the context of COVID-19, underscoring the need for more comprehensive research on its health implications.

Health implications of cannabis use

Cannabis use can have various health implications, both positive and negative, depending on the frequency, method of consumption, and individual factors. 

Therapeutic benefits 

Some studies suggest that cannabis can provide therapeutic benefits, such as pain relief, reduction of nausea and vomiting in chemotherapy patients, and improved appetite in individuals with HIV/AIDS. 

Additionally, certain compounds in cannabis, like CBD, are being researched for their potential to reduce anxiety and seizures.

Mental health

However, cannabis use also carries risks. Frequent use, especially from a young age, has been linked to cognitive impairments, including problems with memory, attention, and learning. 

There is evidence suggesting that heavy use can increase the risk of developing mental health issues, such as anxiety, depression, and psychosis, particularly in individuals with a predisposition to these conditions. 

Respiratory risks 

Smoking cannabis can also have respiratory effects similar to those of tobacco, including chronic bronchitis and lung irritation. 

While vaping or ingesting cannabis can mitigate some respiratory risks, these methods are not without their own potential health concerns.

The study is published in the journal JAMA Network Open.


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