Marijuana smoking and asthma: a protocol for a meta-analysis

Cannabis - a Rewritten History and Its Pulmonary Consequences

Cannabis presents itself as another challenge of the last decade. Better and better deciphered through in-depth studies, this drug remains a source of scientific debates. Legalized in some states, it competes with tobacco regarding the effects generating respiratory symptoms, chronic bronchitis, bronchial cancer, respiratory infections, etc. In this article we will review the pharmacology, epidemiology, clinical and prevention aspects and try to demonstrate which of these are the most effective means of prevention. This review proves once again that this drug has many hidden dangers.

Inhaled Marijuana and the Lung

Although vaping has recently increased as a mode of inhaling marijuana and has been associated with numerous and sometimes fatal cases of acute severe lung injury, smoking remains the most common method of inhaling marijuana and has been studied more extensively. Smoking marijuana has been shown to produce modest but significant short-term bronchodilation both in healthy subjects and those with asthma. Long-term effects of habitual marijuana smoking include the following: 1) symptoms of chronic bronchitis (increased cough, sputum production and wheezing); 2) modest effects on lung function in cross-sectional studies (no significant decrease in forced expired volume in 1 second [FEV₁) but mild reductions in FEV₁/forced vital capacity ratio [FEV₁/FVC], an increase in FVC and other lung volumes, reductions in specific airway conductance, and variable effects of maximal mid-expiratory flow rates and diffusing capacity; and 3) variable effects on age-related decline in FEV1 in longitudinal studies. Most cohort and case-control studies have failed to show that marijuana smoking is a significant risk-factor for lung cancer despite the presence of pro-carcinogenic components in marijuana smoke, although further study is warranted. The question whether marijuana smoking is associated with asthma is unclear and requires further investigation. Although delta-9 tetrahydrocannabinol (THC), the principal psychoactive component of marijuana, has immunomodulatory properties that hypothetically could increase the risk of pneumonia, the few available studies in marijuana smokers have failed to find an increased risk of pneumonia in immunocompetent users, although effects in immunosuppressed individuals have been variable.