Marijuana smoking does not harm the lungs, oddly enough:
In the new study, which was published in The Journal of the American Medical Association and financed by the National Institutes of Health, roughly 5,100 men and women in four cities – Oakland, Calif.; Chicago; Minneapolis; and Birmingham – were interviewed and given lung function tests repeatedly over 20 years. They were on average about age 25 at the start, and more than half smoked marijuana, cigarettes or both.
The researchers found that for marijuana smokers, an exposure of up to seven “joint years” — with one joint-year equivalent to smoking 365 joints or filled pipes, or an average of one joint a day for seven years — did not worsen pulmonary function. Dr. Kertesz noted that with heavier marijuana use, described as 10 joint-years of exposure or more, lung function did begin to decline. And for a person who smokes both marijuana and cigarettes, “the net effect is going to be continued loss of lung function.”
Dr. Donald Tashkin, a pulmonologist at the University of California, Los Angeles, who has studied marijuana for over 30 years and was not involved in the study, said it confirmed findings from several other studies showing “that essentially there is no significant relationship between marijuana exposure and impairment in lung function.” He said one reason marijuana smoke may not be as harmful as tobacco smoke, despite containing similar noxious ingredients, may be the fact that its active ingredient, THC, has anti-inflammatory effects.
Or perhaps that they were looking at the equivalent of only smoking one joint per day. If the cigarette smokers were only smoking one cigarette per day it would probably take 10 years or more before damage started showing up.