Cannabis use is becoming increasingly common in the United States, with many states legalizing marijuana and expanding access through dispensaries1 . Recent research indicates that cannabis users may face a higher risk of severe COVID-19 outcomes, including hospitalization and intensive care unit (ICU) admission2 . However, some studies report conflicting findings, suggesting that the relationship between cannabis use and COVID-19 severity is complex and requires further investigation3 .
Cannabis and Severe Viral Infection Risk
Cannabis contains over 500 chemical compounds, with tetrahydrocannabinol (THC) and cannabidiol (CBD) being the most studied4 . These cannabinoids interact with the body’s endocannabinoid system, which plays a key role in modulating immune and inflammatory responses relevant to viral infections such as COVID-195 46. While some laboratory studies suggest that cannabinoids like CBD can inhibit SARS-CoV-2 replication and reduce inflammation, clinical evidence on their effects in COVID-19 patients remains limited and inconclusive7 8.
A large retrospective cohort study involving 72,501 COVID-19 patients found that about 10% were current cannabis users9 . After adjusting for confounding factors including tobacco smoking, cannabis use was associated with an 80% increased risk of hospitalization and a 27% increased risk of ICU admission among COVID-19 patients9 . Notably, no significant difference in mortality risk was observed between cannabis users and non-users9 . Tobacco smoking, a well-established risk factor, was linked to higher mortality and ICU admission rates in COVID-19 patients10 11.
The mechanisms behind cannabis’ impact on COVID-19 severity may involve lung tissue vulnerability. Inhaling marijuana smoke could injure delicate lung tissue similarly to tobacco smoke, increasing susceptibility to severe respiratory infections12 . Additionally, cannabis’ immunosuppressive effects might impair the body’s ability to fight viral infections effectively10 5.
| Factor | Effect on COVID-19 Severity | Source |
|---|---|---|
| Cannabis use | ↑ Hospitalization (80%), ↑ ICU admission (27%) | 109 |
| Tobacco smoking | ↑ Mortality, ↑ ICU admission | 1011 |
| Cannabis chemical diversity | Unknown individual effects | 105 |
“Chen et al. stated that cannabis use is not harmless in the context of COVID-19. They found that 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.”
— Chen et al. 2
Other substance use, such as alcohol abuse and vaping, was also noted among some patients and may contribute to worse COVID-19 outcomes, though data are limited13 .
Key points on cannabis and COVID-19 severity:
- Cannabis use is linked to increased hospitalization and ICU admission risk in COVID-19 patients9 .
- Tobacco smoking independently raises mortality and ICU admission risks11 .
- The chemical diversity of cannabis complicates understanding individual compound effects5 .
- Cannabis smoke inhalation may damage lung tissue, increasing infection severity12 .
- Cannabis’ immunosuppressive properties could impair immune defense against SARS-CoV-25 .
“In a large-scale retrospective cohort study examining the association of cannabis and tobacco use with COVID-19 outcomes using electronic health records, Griffith et al. reported that self-reported current cannabis users (N=7060), after adjusting for tobacco use and other relevant covariates, were more likely than nonusers to be hospitalized with COVID-19 (OR 1.80; 95% CI 1.68-1.91). Additionally, among the 5749 current cannabis users who were hospitalized, they were more likely than nonusers to require ICU admission (OR 1.27; 95% CI 1.14-1.41), suggesting greater severity of COVID-19.”
— Donald Tashkin, MD, David Geffen School of Medicine at UCLA14
Need for More Research on Conflicting Data
Despite evidence linking cannabis use to more severe COVID-19 outcomes, some studies report contradictory findings. For example, a retrospective cohort study of hospitalized patients found that recent cannabis use was associated with lower COVID-19 severity, including reduced ICU admission and mechanical ventilation needs15 . Another study reported that cannabis users had better clinical outcomes and lower mortality compared with non-users16 17.
These conflicting results may be explained by differences in study design, sample size, and cannabis use patterns. The study showing protective effects assessed past-month cannabis users, while the larger study linking cannabis to worse outcomes included all current users without specifying recency14 . The pharmacologic effects of cannabinoids, which are fat-soluble and stored in fatty tissues for up to 30 days, may vary depending on the timing and frequency of use14 . Recent users might experience immunosuppressive effects that reduce the hyperinflammatory “cytokine storm” seen in severe COVID-19, potentially improving outcomes15 14.
Additional factors complicating research include:
- Variability in cannabis consumption methods (smoking, vaping, edibles) and doses13 18.
- Differences in study populations, such as hospitalized-only cohorts versus broader clinical samples15 .
- The complex chemical composition of cannabis, with over 500 compounds whose individual effects are not fully understood10 5.
- Potential biases such as collider bias and confounding by other substance use or comorbidities15 14.
Cannabis use and COVID-19 severity remain areas of active investigation. While some data link cannabis to increased hospitalization and ICU admission, other studies suggest recent use may reduce severe outcomes. This highlights the complexity of cannabis’ effects on immune responses and the need for further research. 14159
Researchers emphasize the need for unbiased, rigorous studies that carefully evaluate cannabis use frequency, recency, product types, and routes of administration to clarify its impact on COVID-19 severity and recovery5 419.
Challenges and considerations in cannabis-COVID-19 research:
- Conflicting findings on cannabis’ protective versus harmful effects15 14.
- Importance of assessing recency and frequency of cannabis use14 .
- Influence of cannabis chemical diversity on immune and viral responses5 .
- Potential confounding by tobacco smoking and other substance use9 13.
- Variations in COVID-19 variants, treatments, and vaccination status over study periods14 .
