My guess is that pot smoking does damage the lungs. Maybe not as badly as cigarettes. But you won't find anybody in any area of the medical field who'll tell you that inhaling burning vegetable matter of any kind into your lungs is healthy. You'll get an occasional pot fan telling you, "No, no, it's good for you and won't hurt you at all," but they don't know that for certain. That, to me, is just about as silly as the "pot-cures-all-ills" attitude.

The thing is that, even in the few studies that have been done, large numbers of people haven't been studied over the long term. And the fact that weed's illegal makes it hard to conduct really good, objective studies. There's another problem, too. That's that it's expensive and difficult to examine lungs. A chest x-ray, CT scan or MRI give you some basic details, but a lung biopsy is what really details damage precisely. Lung biopsies are painful and invasive, and they require people to be anesthetized. The most definitive way to assess lung damage is through a close post-mortem examination.

I'm sure grass is very much like cigarettes in that it affects different people different ways--and with varying degrees of severity at different times. Permananent damage may occur for some people after a year, and for others it may not occur until after five years or longer. Just depends on a whole host of other factors like age, gender, physical condition, pre-existing lung health, genetic tendencies, etc.