Cannabis Use Not Linked to COPD, Other Tobacco-related Health Risks
Despite advances in medicinal cannabis continually making headlines, the drug remains highly stigmatized in the public eye. The health benefits of cannabis are often weighed against the risks associated with smoking other substances such as tobacco, but is this a fair comparison?
A recent literature review conducted by researchers at the Imperial College London Institute of Clinical Sciences and the Respiratory Medicine unit in Hammersmith Hospital aims to answer this question. The review attempts to collate and summarize the current state of research into cannabis’ effect on respiratory health, as well as make recommendations to fellow healthcare professionals on how to act with these findings in mind.
Conditions Commonly Associated with Smoking
Chronic Respiratory Effects
Tobacco use is the leading causative factor in the development of chronic obstructive pulmonary disease (COPD). While most of the outward symptoms of COPD can be fairly mild, such as breathlessness and chronic coughing, the symptoms can dramatically worsen over time and in many cases can become fatal. A recent profile on the disease completed by the World Health Organization (WHO) reveals that there are over 250 million cases of COPD worldwide, and it is responsible for around 5% of deaths globally each year.
With COPD already being a significant public health crisis, it is important to identify whether cannabis use will be a contributor, as this is only expected to rise with more states and countries legalizing or decriminalizing cannabis use.
The literature review concluded that based on studies of current cannabis smokers, cannabis use can indeed cause some COPD-like symptoms such as chronic bronchitis, but there were no recorded instances of shortness of breath or irreversible airway damage observed as would be typical in COPD. Further review of studies on former cannabis users showed a clear reduction in this coughing severity and the risk of developing chronic bronchitis later in life. This would appear to indicate that the respiratory effects of cannabis use are somewhat reversible.
There is no clear reason as to why cannabis does not cause COPD in the same manner as tobacco use, though some researchers have theorized that the bronchodilatory, immunomodulatory, and anti-inflammatory effects of cannabis might be relevant factors.
Despite cannabis use not appearing to be linked to COPD, there have been some noted differences between tobacco users, cannabis users, and non-smokers when taking the diagnostic test for COPD.
COPD is most commonly diagnosed by measuring the patient’s FEV1/FVC ratio, where the FEV1 is the Force Expiratory Volume in the first 1 second, and FVC is the Forced Vital Capacity of the lungs. A ratio of lower than 0.70 is usually considered a good indicator of COPD or a similar respiratory airflow limitation.
By examining several large-scale studies of long-term cannabis users, the researchers found that cannabis users do have a lower FEV1/FVC ratio than non-smokers, but unlike tobacco smokers who have abnormally low FEV1 values, the poor ratio for cannabis users is due to an increase in FVC of the lungs with no significant change in FEV1.
There are no proven hypotheses as to why cannabis users have an abnormally high FVC, though the leading theory postulates that breath-holding techniques used by cannabis users could be a factor.
Bullous Lung Disease
Cannabis has also been anecdotally linked to bullous lung disease - a condition resulting in “bullae” (abnormal airspaces) being present in lung tissue which can negatively impact lung function. Bullous lung disease is known to further degenerate into the creation of a pneumothorax, a sizable pocket of free air in the lung that can lead to lung collapse.
Despite this link between cannabis, bullous lung disease, and pneumothorax being fairly well-established in healthcare circles, the literature review revealed that there is actually scant scientific information that supports this linkage.
The researchers found that as of 2018, there had been 7 case series and 11 case reports published on the topic; covering only 57 cases. Importantly, in all but four of these cases the patients were also concurrently smoking tobacco, and so it becomes hard to elucidate exactly what effects are the result of cannabis.
The reviewers also identified the presence of one 2007 cross-sectional study which attributed lower density lung regions in cannabis users to hyperinflation rather than bullae in the lung.
It appears very clear that more research is needed in order to establish any solid links between cannabis use and bullous lung disease or hyperinflation. Future studies should also ensure endeavor to detail the effects on cannabis users, tobacco users, concurrent users of both, and non-smokers in order to gather more epidemiological data.
One of the most well-known risks of tobacco smoking is the increased risk of lung cancer and associated respiratory cancers. This is due to tobacco containing a significant number of compounds that are carcinogens, or become carcinogenic when burned, that are then inhaled into the lungs.
Similar carcinogens are present in cannabis material, and so cannabis has long been suspected of having a similar cancer-related risk. Additionally, premalignant changes have also been recorded as being observed in bronchial biopsies from long-term cannabis users.
Despite this, there appears to be no clear scientific study that can prove a link between cannabis use and increased lung cancer risk. There is a Swedish study of army conscripts that observed cannabis users as having a two-fold greater risk of developing lung cancer, but the literature review authors point out that the study did not adequately assess the smoking history of the recruits as it simply recorded smoking status at the time of conscription and did not routinely monitor any changes to this over the course of the study. A more recent pooled analysis of six case studies showed no signs of increased lung cancer risk between cannabis users and non-smokers.
It is not currently known why cannabis use is not linked to cancer risk in a similar way to tobacco use, but the most likely hypothesis points to the anti-inflammatory and anti-neoplastic nature of some cannabinoids causing some kind of protective effect that hampers cancer cell proliferation.
Consequences of this Review
From this review, it is clear that the long-term effects of cannabis use are significantly different from those associated with tobacco use; though the reasons behind this difference remain for the most part unclear.
Crucially, there is no evidence to support cannabis being linked to COPD, and many of the respiratory health problems that are observed are reversible upon quitting cannabis use. For other conditions, such as lung cancer, more investigation into the general anti-inflammatory and anti-neoplastic mechanisms of cannabis and its constituent cannabinoids could help identify why smoking cannabis affects the body in such a starkly different way to smoking tobacco products.
This literature review highlights many examples of well-crafted studies, however, there are also examples of studies that could have offered even more valuable information if drug use histories had been taken in greater detail. This would allow researchers to more clearly differentiate between the effects of cannabis and tobacco in addition to providing specific information regarding the effects on people who concurrently use both drugs. It is the recommendation of the reviewers that primary and secondary healthcare professionals should integrate taking a detailed history of inhalational drug use into their routine when assessing respiratory problems.