Cannabis, Cigarette Smoking and Lung Function –not all downhill?
Philip W. Ind
Respiratory Medicine Imperial College London
The adverse effects of cigarette (tobacco) smoking are well established and well known. Cannabis (also called marijuana) is the most widely used illicit drug and the second most smoked substance. In its various forms it has been increasingly licensed for recreational as well as medical use. Cannabis contains many pharmacologically active substances and cannabinoid pharmacology is very complex. Much is known about its psychoactive properties but rather less about its pulmonary effects. Cannabinoids have well documented anti-inflammatory and immunomodulatory effects. This review explores the information available regarding its effects on the lungs.
In normal subjects acute exposure to inhaled and oral marijuana produces substantial bronchodilatation. This also occurs in asthmatic subjects and patients recovering from an asthma exacerbation. Less information is available in COPD.
Epidemiological information about chronic exposure to marijuana is compounded by the difficulties of studying an illicit substance, the problems of variability in composition and quantification of consumption and the fact that it is usually smoked in combination with tobacco. Available data suggest that cannabis smoking commonly leads to chronic bronchitis (cough and phlegm). However, surprisingly it does not generally cause progressive airflow obstruction and COPD. It produces an increase in vital capacity rather than a fall in FEV1. It has been associated with the development of bullous lung disease but not definite emphysema in the limited studies. It does not seem to be associated with lung cancer nor with frequent respiratory infections