Speaking as someone who would make a definitive study of one, I was pleased to read that marijuana smoking apparently does very little lung damage:

Via Vulture:

A government study, one of the most extensive examinations ever of the long-term effects of marijuana use, has found that smoking one joint a day for 7 years, or one joint a week for 49 years, does not impair lung function. In fact, “marijuana users performed slightly better on the lung function test” than people who don’t smoke anything. The study did not measure the effects of smoking a joint the size of a zucchini.

I might be able to help out there…

Marijuana Smoking Does Not Harm Lungs, Study Finds (New York Times)