“Smoking a joint once a week or a bit more apparently doesn’t harm the lungs, suggests a 20-year study that bolsters evidence that marijuana doesn’t do the kind of damage tobacco does…

The analyses showed pot didn’t appear to harm lung function, but cigarettes did…”
Read more: http://www.foxnews.com/health/2012/01/11/marijuana-doesnt-appear-to-harm-lung-function-study-finds/