Only three states in the United States ― Idaho, Kansas, and Nebraska ― do not allow any use of cannabis/marijuana. The other 47 states and the District of Columbia allow the use of cannabis for medical purposes, with 24 of those states also allowing its recreational use. So, having a patient ask about cannabis in some form – its dangers or its benefits – is likely becoming more common in your practice.
Unfortunately, there are more questions than definitive answers about the effects of cannabis on the lungs and other medical conditions due to US Drug Enforcement Administration research restrictions. More data has been collected internationally, but only 20 to 30 groups of investigators have looked at the effects of marijuana on the lungs over several decades, according to pulmonologist Donald P. Tashkin, MD. A distinguished emeritus professor of medicine at the David Geffen School of Medicine at UCLA Health Sciences, Dr. Tashkin has studied the effects of cannabis for more than 50 years and notes that cannabis study methods and results often are inconsistent.
Still, the American Lung Association (ALA) states one certainty: “Smoking marijuana clearly damages the human lung, and regular use leads to chronic bronchitis and can cause an immune-compromised person to be more susceptible to lung infections.”
Cannabis Impact Data is Coming, but Slowly
The links between cannabis and other lung and respiratory diseases, such as lung cancer, chronic obstructive pulmonary disease (COPD), asthma, emphysema, and COVID, are less clear. Yet, data are slowly being collected about each of these diseases, as well as differences between smoking and vaping cannabis, and the comparative effects of marijuana and tobacco smoke.
The US Food and Drug Administration has not approved a marketing application for cannabis for the treatment of any disease or condition. It has approved one cannabis-derived drug product, cannabidiol (Epidiolex), and three synthetic cannabis-related drug products: dronabinol (Marinol) for epileptic seizures; dronabinol (Syndros) for chemotherapy-induced nausea and vomiting as well as anorexia related to weight loss in patients with AIDS; and nabilone (Cesamet) for chemotherapy-induced nausea and vomiting.
Roger Zoorob, MD, MPH, the Richard M. Kleberg Senior Professor and Chair of the department of family and community medicine at Baylor College of Medicine, suggested that when discussing cannabis use with patients, physicians can avoid confusion by focusing on what is known.
“I make sure they know that definitely, marijuana slows you down and it can cause accidents,” he said. “For adolescents and young adults, I explain that using it at a young age affects development and mental health, and predisposes to more addiction. For the elderly, it increases the heart rate and can affect falls and the cardiovascular system. I warn against its use in the prenatal period or if they are planning to get pregnant, similar to using alcohol.”
Dr. Zoorob, who has a professional interest in substance use disorders in primary care and tracks cannabis research, said that as more patients ask questions about the long-term effects of cannabis, he provides them with easy-to-read literature.
Cannabis research is dynamic and still developing, so its findings about the effects on various diseases and its route of administration can be controversial, Dr. Tashkin added.
Below is a brief look at what is known about some of the most common lung and respiratory conditions with regard to cannabis use impact.
Asthma
Various studies have demonstrated that THC found in marijuana smoke has bronchodilatory effects, leading some to assume that it may help manage asthma, but there also is evidence that cannabis smoking may be a risk factor for the development of asthma, Dr. Tashkin said. “The question whether marijuana smoking is associated with asthma is unclear and requires further investigation,” he added.
Dr. Zoorob was emphatic that family healthcare professionals reject the use of cannabis by patients with asthma. “People with existing upper respiratory disease – asthma or chronic bronchitis – definitely should not smoke anything, whether it is a joint or cigarettes,” he said.
Chronic Bronchitis
Chronic bronchitis is defined on the basis of symptoms – having a productive cough that lasts at least 3 months and over the course of 2 years. Cigarette smoking is a leading cause of chronic bronchitis, according to the American Lung Association (ALA).
“Chronic bronchitis clearly is associated with marijuana smoking,” Dr. Tashkin said, adding that a recent study published in Respiratory and Critical Care Medicine, showed that tissue samples of marijuana-only smokers had the same widespread abnormalities as tobacco smokers.
COPD
The CDC states that more research is needed to understand the specific effects cannabis smoking may have on COPD. Tobacco smoke has been linked to the development of COPD, but marijuana smoke contains approximately 100 cannabinoid compounds not found in tobacco, including delta-9-tetrahydrocannabinol (THC), Dr. Tashkin explained. THC has been shown to have immunosuppressive/anti-inflammatory properties mediated by cannabinoid-2 (CB2) receptors, which could have a positive effect on managing COPD.
Additionally, the SubPopulations and InteRmediate Outcome Measures in COPD Study (SPIROMICS), designed to examine the causes and management of COPD, found that neither former nor current marijuana smoking of any amount was associated with evidence of COPD progression or its development, he said.
“In view of the relatively sparse and conflicting literature addressing this issue, additional well-designed studies, especially ones with a larger sample size, longer duration of follow-up, and more accurate assessment of cumulative lifetime marijuana smoking amount, are needed for a better understanding of marijuana smoking as a risk factor for developing COPD,” Dr. Tashkin said.
COVID
A recently published study in JAMA Network Open, Cannabis, Tobacco, and COVID-19 Outcomes, found that cannabis use was associated with an increased risk of hospitalization and ICU admission compared with patients not using cannabis, after controlling for other risk factors. However, comments from Dr. Tashkin published with the study, “Does Recent Cannabis Use Affect Outcomes in Hospitalized Patients with COVID-19?” report that the immunomodulatory effects of cannabis may play a role in inhibiting the development of more severe COVID in recent cannabis users.
The CDC has recommended the use of immunosuppressants in the treatment of patients with severe COVID. Because it has been shown that cannabinoids may have some beneficial effects on some autoimmune diseases, it is conceivable that having smoked marijuana recently – within the past month – may have a beneficial effect for patients with COVID, Dr. Tashkin said.
This research calls for further investigation into the associations of cannabis use with COVID-19 outcomes, he added.
Emphysema
Emphysema can be caused by smoking and air pollution, according to the ALA, but Dr. Tashkin added that research based on CT scans found that marijuana smoking has not been shown to be associated with the most common forms of emphysema. However, a series of case studies has found that heavy marijuana smokers can develop bullous emphysema, which is a severe form of lung destruction. Case series, however, are not proof of causation. Again, well-designed, long-term studies are needed to address this issue, he said.
Bob Hancox, MD, a respiratory epidemiology researcher and physician at the Dunedin School of Medicine, University of Otago, New Zealand, agreed, adding, “Cannabis causes a different pattern of effects on lung function and seems less likely to cause emphysema, except in those severe cases as noted above. The effects are not necessarily less harmful, just different.”
Lung Cancer
The Centers for Disease Control and Prevention (CDC) warns that smoked cannabis can harm lung tissue and cause scarring and damage to small blood vessels, regardless of smoke administration, such as joints, vaping, bongs, bowls, or blunts. However, researchers have conflicting opinions on whether it is linked to lung cancer.
“Five studies show no increased risk for lung cancer due to marijuana. One study showed the opposite,” Dr. Tashkin said. “I think it is unlikely marijuana is a risk for lung cancer, but you cannot be completely certain.”
But, said Dr. Hancox, “The question of whether cannabis smoking causes lung cancer has not been resolved yet. Some studies have found a link, whereas others have not. It seems likely that the risk of lung cancer is increased by smoking cannabis because cannabis smoke contains most of the carcinogens and chemicals found in tobacco smoke, but a definite causal link has not yet been established.”
