weed does affect the lungs as it is a pollutant to your lungs, but it isnt a carcinogen..if that makes sense.....weed doesnt cause you to develop cancer or black lung type diseases if that is what you are asking...anything not air you put into your airway hurts your lungs, that is common sense, but it is the amount you are worried about, and marijuana dosent kill you......

hope this helped some and yes, i am a healthcare professional...

in laymans terms i guess, happy toking...

princess