Smoking joints does not seem to pose as many pulmonary risks as smoking cigarettes, in part because people simply smoke fewer of them. One large study in 2006 found no increased risk of lung cancer. But a French study last year found an "independent role of cannabis in the development of lung cancers." A 2009 study in the U.K. concluded that acetaldehyde, which is present in both marijuana and tobacco smoke, can cause DNA damage "with the possibility to initiate cancer development."
(See pictures of Cannabis Culture.)

The science, however, remains unsettled, and other research has reached opposite conclusions. Another U.K. study showed that the anti-inflammatory properties of cannabis may have an anticancer effect. And a 2009 study in Spain found that tetrahydrocannabinol (THC), the main intoxicating component of pot, can lead human brain-cancer cells to self-destruct—though the study involved introducing the cells into mice and treating them with THC. That's a long way from treating cancer in a human brain.

Read more: http://www.time.com/time/magazine/ar...#ixzz2MxfwxV4T

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