METHODOLOGY: Researchers led by epidemiologist Mark J. Pletcher used a large national database with more than 5,000 respondents to compare the lung function of marijuana and tobacco smokers over a 20-year period. They looked closely at their use of marijuana and tobacco, and measured for airflow and lung volume at years 0, 2, 5, 10 and 20. (Airflow is the amount of air you can blow out of your lungs in one second while lung volume refers to the total amount of air you can blow out after taking the deepest breath possible.)
RESULTS: Repeated inhalation of tobacco smoke causes loss of airflow and lung volumes. Marijuana smoke, however, had the opposite effect, increasing both airflow rates and capacity.
CONCLUSION: Unlike cigarette smoke, use of marijuana does not result in lasting respiratory harm.
