“People who smoke marijuana–even heavy, long-term marijuana users–do not appear to be at increased risk of developing lung cancer…

Marijuana smoking also did not appear to increase the risk of head and neck cancers, such as cancer of the tongue, mouth, throat, or esophagus, the study found.

The findings were a surprise to the researchers. “We expected that we would find that a history of heavy marijuana use–more than 500-1,000 uses–would increase the risk of cancer from several years to decades after exposure to marijuana,” said the senior researcher, Donald Tashkin, M.D., Professor of Medicine at the David Geffen School of Medicine at UCLA in Los Angeles.”

More: http://www.sciencedaily.com/releases/2006/05/060526083353.htm