Of all the nonsense believed by members of the drug culture, among the most ridiculous is the idea that smoking marijuana has no effect on the lungs.

Now, a new study has backed up the common sense notion that smoking marijuana — which usually involves holding smoke in the lungs for several seconds — can be nearly as bad for your health as smoking tobacco. According to this study, smoking a single cannabis joint has the same effect on the lungs as smoking up to five cigarettes — at once.

Published on-line ahead of print in the August 2007 issue of the journal Thorax, this research is based on a study of 339 adults up to the age of 70, divided into four different groups: those who smoked only cannabis (one joint a day for five years); those who smoked tobacco only (one pack of cigarettes a day for at least a year); those who smoked both; and those who smoked neither.

All had high definition scans taken of their lungs and took breathing tests to assess lung function.

The results? Cannabis smokers complained of wheezing, cough, chest tightness and phlegm. While emphysema, the most common and most crippling smoking-related lung disease, was found only in those who smoked tobacco, cannabis still damaged the lungs by reducing the numbers of small fine airways, which are important for transporting oxygen to and from the blood. Cannabis also damaged the large airways of the lung, blocking airflow and straining the lungs.