Two different groups recently published findings related to pulmonary functions and the use of marijuana used either medicinally or recreationally. The conclusions between the two were that use of marijuana to treat breathing abnormalities such as Chronic Obstructive Pulmonary Disease (COPD) was ineffective and that even with casual, once-a-week use, the consequences of cannabis may include cough and excess phlegm.

One of these studies was led by Dr. Mehrnaz Ghasemiesfe from the University of California, San Francisco, and San Francisco Veterans Affairs Medical Center.

Using predetermined criteria, the study authors reviewed the literature to examine the association between marijuana use and respiratory symptoms, pulmonary function, and obstructive lung disease among adolescents and adults. They identified twenty-two studies that fit the study parameters.

They found that, among the prospective studies, two found an association of risk for cough and increased phlegm production. The cross-sectional studies also showed that marijuana use was associated with a cough and increased phlegm as well as wheezing and dyspnea.

They did not identify studies that had adequate data to draw conclusions of efficacy related to pulmonary function or changes in obstructive lung disease.

A group of researchers from McGill University in Montreal looked at cannabis-related treatments for COPD. Sara J. Abdallah, a Ph.D. candidate in exercise physiology, along with her colleagues, did not find a difference between vaporized cannabis and the use of placebo in lung volumes or heart rate during exercise. They used a crossover study to evaluate 16 patients having advanced COPD.

All patients were already on optimum therapy for their disease and using different kinds of inhalation therapies. The participants were randomly given inhaled cannabis or a placebo prior to exercise and then crossed over at a different session of exercise.

The authors do state that the study had participants already on optimum therapy, so further research is warranted, especially given that cannabis use, particularly when inhaled, can have uncomfortable long-term consequences.

"We know that smoke from tobacco and other entities — including burning wood in your fireplace — causes chronic bronchitis, so it's not at all surprising they found chronic bronchitis in prior marijuana research," said Dr. Norman Edelman, senior scientific adviser to the American Lung Association.

More and more states are approving the use of marijuana for adult recreation. Edelman expressed concern over the health consequences, "You would worry about people being more susceptible to pneumonia, and of course, the end result of chronic bronchitis, if it persists long enough and is severe enough, is what we call COPD — chronic obstructive pulmonary disease." About half of tobacco smokers get COPD, he continued.

"It will be interesting to see what percentage of regular marijuana smokers get COPD," he added. Time will tell as more adults and adolescents use inhaled cannabis.