So far, marijuana alone has not been shown to increase the risk of developing COPD. A new study shows that marijuana combined with tobacco smoking more than triples the risk of COPD, perhaps because marijuana makes the lungs more susceptible to damage from tobacco smoke.
The study, published in the April 13 issue of CMAJ examined the effect of smoking both tobacco an marijuana, using incentive spirometry to measure lung function in 878 individuals, age 40 or above, in Vancouver Canada.
Guidelines for the study included smoking at least 365 cigarettes per lifetime, and any history of marijuana smoking as self-reported by the study participants.
Dr. Wan Tan of the University of British Columbia and St. Paul's Hospital and coauthors found… “a significant synergistic effect between marijuana smoking and tobacco smoking. This effect suggests that smoking marijuana (at least in relatively low doses) may act as a primer, or sensitizer, in the airways to amplify the adverse effects of tobacco on respiratory health.”
The study results do not show an association between COPD and smoking marijuana. Marijuana potency, smoking marijuana combined with tobacco in one cigarette, and depth of inhalation were not taken into consideration for the study. Other factors may need to be considered in evaluating the risk of tobacco and marijuana combined and increased COPD risk.
The study authors specifically looked at people over 40, who were less likely to smoke tobacco, to measure the effect of marijuana and tobacco combined and increased COPD risk.
Dr. Want Tan and colleagues write, “Although our study had insufficient power to show an association between marijuana alone and increased risk for COPD, it remains uncertain whether marijuana by itself is harmful for the lungs. Larger studies are needed to address this critically important issue in the future."
The study also showed that a combination of smoking marijuana and tobacco led to 2.5 times the risk of developing respiratory symptoms.