drugs

http://www.sciam.com/article.cfm?chanID=sa003&articleID=0002491F-755F-1473-B55F83414B7F0000

The smoke from burning marijuana leaves contains several known carcinogens and the tar it creates contains 50 percent more of some of the chemicals linked to lung cancer than tobacco smoke. A marijuana cigarette also deposits four times as much of that tar as an equivalent tobacco one. Scientists were therefore surprised to learn that a study of more than 2,000 people found no increase in the risk of developing lung cancer for marijuana smokers.

“We expected that we would find that a history of heavy marijuana use–more than 500 to 1,000 uses–would increase the risk of cancer from several years to decades after exposure to marijuana,” explains physician Donald Tashkin of the University of California, Los Angeles, and lead researcher on the project.