The Institute of Medicine concluded in its Mar. 1999 report titled "Marijuana and Medicine: Assessing the Science Base":
"A number of animal studies have revealed respiratory tract changes and diseases associated with marijuana smoking, but others have not. Extensive damage to the smaller airways, which are the major site of chronic obstructive pulmonary disease (COPD), and acute and chronic pneumonia have been observed in various species exposed to different doses of marijuana smoke. In contrast, rats exposed to increasing doses of marijuana smoke for one year did not show any signs of COPD, whereas rats exposed to tobacco did."
Can Marijuana Help People with Asthma or Other Breathing Disorders?
Nature, a peer-reviewed scientific journal, stated in a Nov. 2, 2000 article titled "Bidirectional Control of Airway Responsiveness by Endogenous Cannabinoids" by Calignano et al.:
"Smoking marijuana or administration of its main active constituent, THC, may exert potent dilating effects on human airways. But the physiological significance of this observation and its potential therapeutic value are obscured by the fact that some asthmatic patients respond to these compounds with a paradoxical bronchospasm [constriction of the air passages of the lung].
The mechanisms underlying these contrasting responses remain unresolved. Here we show that endogenous cannabinoid anandamide exerts dual effects on bronchial responsiveness in rodents: it strongly inhibits bronchospasm and cough evoked by the chemical irritant, capsaicin, but causes bronchospasm when the constricting tone exerted by the vagus nerve is removed."
Daniele Piomelli, PhD, Professor of Pharmacology at the University of California at Irvine, told Reuters in 2000:
"We think that by targeting cannabinoid receptors in the upper airways we can control coughs in a number of conditions...That's important because most treatments currently available basically act on the brain cough center, a small region of the brain that is the target for codeine and similar drugs."
Donald P. Tashkin, MD, Professor of Pulmonary Care at the University of California, Los Angeles, stated in a 1975 article titled "Effects of Smoked Marijuana in Experimentally Induced Asthma" in the American Journal of Respiratory and Critical Care Medicine:
"After exercise induced bronchospasm, [exercise-induced asthma] placebo marijuana and saline were followed by gradual recovery during 30 to 60 min, whereas 2.0 per cent marijuana... caused an immediate reversal of exercise-induced asthma and hyperinflation."
The New England Journal of Medicine, a peer-reviewed medical journal, published a 1973 study titled "Single-Dose Effect of Marihuana Smoke. Bronchial Dynamics and Respiratory-Center Sensitivity in Normal Subjects," by L. Vachon et al., that stated:
"Marihuana smoke, unlike cigarette smoke, causes bronchodilation [expansion of the air passages] rather than bronchoconstriction [narrowing of the air passages] and, unlike opiates, does not cause central respiratory depression."
Donald P. Tashkin, MD, Professor of Pulmonary Care at the University of California, Los Angeles (UCLA), stated in a June 2005 article published in the Monaldi Archives for Chest Disease:
"The smoke of marijuana, like that of tobacco, consists of a toxic mixture of gases and particulates, many of which are known to be harmful to the lung.... Whereas THC [primary active ingredient in marijuana] causes modest short-term bronchodilation [expansion of the air passages], regular marijuana smoking produces a number of long-term pulmonary consequences, including chronic cough and sputum, [and] histopathologic evidence of widespread airway inflammation."
The Institute of Medicine's Mar. 1999 Report stated on page 113:
"Results of human studies suggest that there is a greater chance of respiratory illness in people who smoke marijuana...
When marijuana smokers were compared with nonsmokers and tobacco smokers in a group of 446 volunteers, 15-20% of the marijuana smokers reported symptoms of chronic bronchitis, including chronic cough and phlegm production...Habitual marijuana smoking is associated with changes in the lining of the human respiratory tract.
Many marijuana or tobacco smokers have increased redness (erythema) and swelling (edema) of the airway tissues and increased mucous secretions."
Wayne Hall, PhD, Director of the Institute for Molecular Bioscience at the University of Queensland and Nadia Solowij, PhD, Research Fellow of Psychology at the University of Wollongong, stated in a Nov. 14, 1998 article titled "Adverse Effects of Cannabis" published in The Lancet:
"Lung function is significantly poorer and there are significantly greater abnormalities in the large airways of marijuana smokers than in non-smokers."