Marijuana is widely used in the United States. Despite its federal status as a Schedule I drug, several states have legalized marijuana for medical and recreational use. Thus, researchers seek to determine how marijuana use may interact with the ongoing COVID-19 pandemic. While most evidence suggests smoking marijuana could put COVID-19 patients at greater risk, some compounds in marijuana are promoted as treatments for the viral infection. This post will compile research demonstrating these potential interactions between marijuana use and COVID-19.

Many of the proposed negative effects of marijuana use for COVID-19 patients relate to the recently documented neurological effects of SARS-CoV-2 infection (Archie, 2020). In a retrospective analysis of case studies, Mao et al (2020) showed that a third of patients with COVID-19 present neurological symptoms related to the central nervous system (e.g. headaches) or the peripheral nervous system (e.g. taste impairment).  Further, traces of SARS-CoV-2 have been found in the cerebrospinal fluid of deceased patients, adding weight to the claim that the virus can damage the central nervous system (Xiang, 2020). These neurological effects may be a result of secondary bacterial infections that damage the blood brain barrier (BBB), causing greater disruption to the central nervous system (Wu, 2020). Altered integrity of the BBB could influence the development of severe neurological COVID-19 symptoms. Marijuana use may contribute to these issues, specifically through smoke inhalation. Cigarette smoke is known to damage the BBB by triggering oxidative stress (Kaiser, 2015). Furthermore, tetrahydrocannabinol (THC), the primary psychoactive compound in marijuana, was demonstrated to cause oxidative stress by a similar mechanism in a preclinical study (Wolff, 2015). This suggests that smoking marijuana could induce oxidative stress and damage to the BBB. If this is the case, marijuana use could put a patient with COVID-19 at risk of developing serious neurological symptoms by disrupting the integrity of the BBB, increasing susceptibility to secondary bacterial infection and viral encephalitis. To the contrary, other studies have shown certain cannabinoids to have antioxidant effects, so these hypotheses remain speculation (Atalay, 2020).

Marijuana smoke has also been proposed to have similar cardiopulmonary effects to cigarette smoke (NIDA, 2020), though this is currently debated. Smoking-associated cardiopulmonary damage is of great importance because severe COVID-19 symptoms are generally respiratory. In fact, cigarette smoking is linked with the development of serious COVID-19 symptoms (Vardavas, 2020). If marijuana smoke does have similar health effects to cigarette smoke, then marijuana use could put COVID-19 patients at risk of severe disease progression. It was also recently proposed that smoking could put someone at higher risk of infection with SARS-CoV-2 due to upregulation of ACEII, a target for the virus (Brake, 2020). It is possible that marijuana smoke could cause a similar upregulation because of its shared cardiopulmonary effects with cigarette smoke. Overall, the interactions between marijuana use and COVID-19 are not entirely clear, but it is likely that any kind of smoking is unwise during a respiratory disease pandemic.

One potential negative effect of marijuana use that may impact risk for contracting COVID-19 is reduced vigilance among marijuana users. Vidot et al (2020) found in an online survey of self-reported medicinal cannabis users that only 2.1% of respondents claimed to have been tested for SARS-CoV-2. This testing rate is much lower than the rate found in Canada at the time of the survey (The Government of Canada, 2020). This suggests that medical marijuana users may be less likely to get tested for COVID-19 and could be more disposed to transmitting the virus while unaware of their infection. Additionally, sharing marijuana cigarettes is a common practice that could pose a risk of transmitting the virus between individuals through saliva (El Biali, 2020). Marijuana users, therefore, may be more likely to unknowingly transmit the virus between one another.

To date, there is no evidence of a direct interaction between any of the compounds in marijuana and SARS-CoV-2 infection. That said, interest in marijuana use as a treatment for COVID-19 lies solely in preclinical studies of cannabidiol (CBD), a non-psychoactive component in marijuana being studied for its medical use. CBD may improve lung function and reduce inflammation in animal models. Vuolo et al (2019) demonstrated that CBD reduced lung and airway inflammation in rodent models of asthma, and Ribeiro et al (2015) found a similar effect of CBD administration in mice after acute lung injury. Uncontrolled release of pro-inflammatory cytokines is related to poor outcomes in patients infected with SARS-CoV-2 because of a severe immune reaction known as a cytokine storm (Huang, 2020). CBD, therefore, has been proposed as a treatment to mitigate some of the threats associated with cytokine storms to COVID-19 patients (Esposito, 2020). CBD may help reduce cytokines and inflammation by acting as mild agonist for a hormone receptor called PPAR_λ (O’Sullivan and Kendall, 2010). In agreement with CBD’s observed effect on lung impairment resembling COVID-19 symptoms, PPAR_λ agonists reduce acute and chronic pathologies following influenza virus infection in mice (Huang, 2019). Overall, CBD shows some promise in promoting lung function during respiratory illness. However, CBD is just one compound out of hundreds that exist in marijuana. THC, the main psychoactive component of marijuana is generally found in higher levels than CBD in marijuana products, with some products containing almost no CBD. Thus, these findings may not be generalizable to the effect of marijuana use at the population level.

While there are proposed benefits of CBD during respiratory illness, its effects on COVID-19 have not been studied and it is unclear whether any benefits would outweigh the probable negative effects of marijuana use in COVID-19 patients. A lack of direct evidence has not stopped companies that sell marijuana and cannabis-related products like CBD from advertising them as potential treatments for COVID-19, against FDA regulations (Shover, 2020). Due, perhaps, to medicinal classification of cannabis in many states, it is common that people assume it to be safe in all contexts. However, considering the potential risk factors related to marijuana use in COVID-19 patients, this sort of misinformation could be dangerous. Groshkova et al (2020) found that, whether in response to these false claims or not, cannabis sales increased dramatically during the first three months of the pandemic.

There is also evidence that adolescent marijuana use has increased during the pandemic, and that adolescents primarily use it alone (Dumas, 2020). This potential interaction between COVID-19 and cannabis use is of special concern because drug use can be particularly dangerous for a developing brain. Studies on the detrimental effects of cannabis typically put great emphasis on the potential psychological problems related to marijuana use starting before adulthood, which include anxiety disorders and psychosis. Stay-at-home orders create widespread boredom that probably drives this increase in adolescent marijuana use, and its effects could be detrimental later in life. As some studies have related early marijuana use to anxiety problems in adulthood, there is concern that such anxiety may be exacerbated by social isolation. If anything about marijuana use during the pandemic can be agreed upon, it is that an increase in early use is a public health concern.

In conclusion, there is no direct evidence of any physiological interaction between marijuana use and COVID-19, but potential neurological consequences and consequences of smoke inhalation make it a possible risk factor for COVID-19 disease progression. Despite this, cannabis and CBD have been advertised as treatments and sales have increased. This sets a dangerous trend, considering that marijuana use may contribute to reduced vigilance, and that adolescent use has increased during the pandemic. It is advisable that marijuana users seriously consider these potential risks associated with their drug use during the COVID-19 pandemic.

Authors: Cory Kittleman and Emma Erickson

Edited by Drs. Robert O. Messing and Emma Erickson, and Niki Garcia-Holmes

Photo by Kimzey Nanney on Unsplash

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