Smoking one marijuana joint does as much damage to your lungs as
smoking up to five cigarettes, according to a new report in the Journal Thorax. 

Researchers tested 339 people picked from a larger study of
respiratory health. Some smoked one joint a day for five years. Some, a
pack of cigarettes daily for at least a year. Some smoked both. Others
didn't smoke.  

Only cigarette smokers suffered from emphysema, but
those who smoked pot suffered dramatic lung damage. The extent of
damage was directly related to the number of joints smoked.