Smoking a joint a week for up to seven years doesn't hurt lung function, according to researchers at the University of California, San Francisco. They came up with that number after following more than 5,000 people for 20 years. The results were just published in JAMA, the Journal of the American Medical Association.
In fact, those occasional pot smokers actually had improvements in some measurements of lung function. That may be due in part to the stretching involved in the deep tokes typical of marijuana use. By contrast, both past and present cigarette smokers had impaired lung function.