A 1997 UCLA School of Medicine study (Volume 155 of the American Journal of Respiratory & Critical Care Medicine) conducted on 243 marijuana smokers over an 8-year period reported the following: "Findings from the long-term study of heavy, habitual marijuana smokers argue against the concept that continuing heavy use of marijuana is a significant risk factor for the development of chronic lung disease." "Neither the continuing nor the intermittent marijuana smokers exhibited any significantly different rates of decline in lung function as compared with those individuals who never smoked marijuana." The study concluded: "No differences were noted between even quite heavy marijuana smoking and nonsmoking of marijuana."

Marijuana does not cause serious health problems like those caused by tobacco or alcohol (e.g., strong addiction, cancer, heart problems, birth defects, emphysema, liver damage, etc.).

http://www.cannabis.com/untoldstory/hemp_9.shtml

Plus, marijuana smoke doesn't affect the small bronchial passages in the lungs where you get bronchitis.