Narrator: This is Science Today. A large national study suggests that low to moderate use of marijuana is less harmful to users' lungs than exposure to tobacco. But study leader Mark Pletcher, an epidemiologist at the University of California, San Francisco, says this is not an "end-all, be-all study" for determining whether or not one should smoke marijuana.
Pletcher: This is a very complex issue that includes a lot of social and political factors and also other health factors. Marijuana has some adverse health consequences that need to be considered, including consequences on the lungs. So, it makes you cough, produce more phlegm, but what our study focused on was really the narrow question of whether or not it affects pulmonary function. And for tobacco smoking, the effects on pulmonary function lead to bad disease: emphysema and chronic bronchitis, the kind of thing that actually is a major cause of death in the United States. But we couldn't find that same effect for marijuana use.
Narrator: For Science Today, I'm