It seems like common sense that people with asthma, a condition where lung function is impaired and breathing may be difficult, should avoid cannabis, considering smoking is the most common way people use the substance. But current scientific research on whether cannabis hurts, or could help, asthma is actually mixed.

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Considering the lack of cohesive, long-term evidence on this complicated relationship, clinicians and scientists argue people with asthma should practice caution with smoking cannabis. They also say young people should abstain altogether, though other forms of consumption, like edibles, present less of a risk and may prove to be helpful down the line. 

What is Asthma? 

Asthma is a condition in which the airways narrow, swell, and produce extra mucus, according to the Mayo Clinic. These symptoms can make breathing difficult, or even impossible, as in the case of an acute asthma attack.

asthma symptoms graphic Source: iStock/Good_Stock
Some people’s symptoms clear up in childhood, while others go on to need medications the rest of their lives in order to control the disease.

Cannabis and Asthma

Substances such as smoke that enters the lungs can aggravate asthma, and cigarettes are a major contributor to breathing problems in asthmatics who smoke, but it’s less well-known how marijuana affects breathing or lung function. According to entities solely espousing conventional medical practice, the American Thoracic Society, for example, oppose the use of cannabis in any form and state that marijuana smoke contains many of the same harmful chemicals as tobacco smoke.

“Though we don’t know if smoking a small amount, about one to two joints a month, over a long period may increase the risk of developing chronic obstructive pulmonary disease. We do know that marijuana can make breathing worse in general in people with lung problems and it can cause large air sacs, called bullae, to develop in the lungs, though this is more likely in people under 45,” said the American Thoracic Society.  

It should be noted that in this study, 53 out of the 56 people studied were also tobacco smokers. Directly contradicting the US Thoracic Society, in 2016, British researchers  stated that many studies that indicate that marijuana smoking is associated with increased air intake and lung capacity.  The cause of this is unclear, but what is known is that the inhaled form of cannabis is capable of exerting acute bronchodilator and anti-inflammatory effects that may alleviate asthma symptoms as well as symptoms in chronic obstructive pulmonary disease (COPD).

More Mixed Research  

There are numerous studies which contradict each other when it comes to studying how cannabis affects airways. 

Research that indicates cannabis might harm breathing

A 2019 Norwegian study compared survey data on 2,602 young adults over 13 years with information on prescription asthma medications gained from a national prescription database.  Factors including current cannabis and tobacco use, gender, age, and education were measured.  The authors found that filling prescriptions for asthma medications were associated with current cannabis use, even after eliminating tobacco use as a risk factor. The study authors said their results suggest smoking cannabis is risky for people with bronchial asthma. 

However in a significant admission, the authors state, “our study cannot completely rule out the possibility of reversed causality, i.e. that patients with asthma use cannabis to relieve symptoms.”  In a rather inexplicable study, cannabis use has also been associated with impairments on a lung-function test in women, according to a 2017 study looking at factors that might get in the way of airway function in people with and without asthma. Both tobacco and cannabis use were associated with breathing test abnormalities, which was seen in women and not men.

“Despite higher lifetime exposure, there were few associations between cannabis and IOS (measurement of airway functioning in the lungs) in men.”

Research that indicates cannabis might not harm breathing

On the other hand, researchers from the National Heart and Lung Institute, Imperial College London analyzed 133 separate studies over 47 years on the “effect of cannabis smoking on lung function and respiratory symptoms.” Their conclusion was that:

  1. “[R]ecent large studies have shown that, instead of reducing forced expiratory volume...and forced vital capacity (defined as the amount of air that can be forcibly exhaled from the lungs after taking the deepest breath possible) marijuana smoking is associated with increased FVC. 
  2. One potential explanation for the absence of chronic airflow obstruction with cannabis smoking may relate to the well-documented anti-inflammatory and immunomodulatory effect of THC.
  3. Chronic marijuana smokers, who often also smoke tobacco, present with similar chronic respiratory symptoms but do not appear to develop airflow obstruction and COPD.”

A 2012 JAMA (Journal of the American Medical Association) report out of the University of California, San Francisco looked at lung function in 5,115 men and women in four US cities and their use over 20 years and concluded, “occasional and low cumulative marijuana use was not associated with adverse effects on pulmonary function.”  A 2018 Annals of Internal of Internal Medicine report by a group of prestigious institutions in the US stated after examining 22 studies:

  1. “Low-strength evidence suggests that smoking marijuana is associated with cough, sputum production, and wheezing. 
  2. Evidence on the association between marijuana use and obstructive lung disease and pulmonary function is insufficient.”

CBD for Asthma

Using animal models, a 2015 study, asthma was induced in 8-week-old rats in order to study the anti-inflammatory potential of CBD. Researchers found that CBD was able to blunt the inflammatory response in the animals, and suggested that the cannabinoid could be a potential new treatment for asthma. 


In summary, because smoking cannabis, just as in tobacco, is associated with chronic cough and greater phlegm production, health experts recommend people with asthma exercise caution.  Of course, there are plenty of other methods to use cannabis without harsh, irritating smoke, including edibles, but it’s best to consult a doctor first before you try anything new.  It is difficult to compare the studies to each other since they’re testing different responses and measuring different outcomes, and cannabis users can also be using tobacco which confuses the results. 

According to a 2016 review that looked at the effects of cannabis on respiratory symptoms and lung function, the most pressing area for further research is to understand why tobacco and cannabis smoke both cause chronic bronchitis symptoms, but have different effects on lung physiology.  The bottom line is that more information is required on cannabis smoking and the lung.