A recent report published in the journal Breathe by scientists in the UK suggests that chronic marijuana smoking may not cause the same deleterious effects on the lungs compared to cigarette smokers. While cigarette smoking has been linked to chronic obstructive pulmonary disease (COPD) and lung cancer, the same cannot be said of marijuana. Specifically, chronic marijuana smokers do not present symptoms of COPD, and there is little evidence to suggest a link to lung cancer.
The report was written by Dr. Luis Ribeiro of Imperial College London and Dr. Philip Ind of Hammersmith Hospital in London. They challenge the assumption that smoking marijuana will lead to the same consequences as cigarettes. They stake their claim on the fact that, while there are few studies out there, those that do exist have found little evidence of a connection. “As healthcare professionals,” they write, “we deal with tobacco all the time, but we also need to know about the respiratory effects of marijuana to be able to advise our patients and colleagues.”
For example, marijuana smokers are less likely to develop COPD than cigarette smokers. To diagnose a patient with COPD, clinicians measure how well your lungs function. According to the authors’ clinical observations, the lungs of chronic marijuana smokers operate normally. This may be due to the respiratory technique many marijuana smokers apply, that is, to breathe in the smoke deeply and hold it longer than cigarette smokers. However, according to the authors, THC has been shown experimentally to cause bronchodilation (opening of the bronchial tubes) whereas cigarettes narrow the bronchial tubes. This bronchoconstriction can contribute to the development of COPD.
The data showing a link between chronic marijuana smoking and lung cancer is more mixed. The authors cite a Swedish study of 50,000 conscripts found a two-fold increase in rates of lung cancer in marijuana smokers than non-smokers forty years later. However, the authors indicate that this study suffered from fundamental flaws, such as only considering smoking history at the time of conscription. On the other hand, a pooled analysis of six studies found no evidence of an increase in the risk of lung cancer. Other studies have found premalignant changes in lung biopsies of marijuana smokers, but this is not enough to conclude that they will develop lung cancer. The authors note THC or other cannabinoids may even prevent lung disease based on marijuana’s reported anti-inflammatory effects.
Despite these differences, there are some shared symptoms between chronic marijuana and cigarette smokers. Both populations can suffer from bouts of coughing, increased sputum production, wheezing, and acute bronchitis. Yet the similarities seem to stop there.
The report concludes that we should not speculate on the health risks of marijuana based on the effects of cigarettes. Nevertheless, the authors warn that the lack of evidence connecting marijuana with lung disease could be due to the low number of studies. More work must be done to state that there is a similarity.