Burning marijuana when smoking releases many other substances than THC. THC does not appear to be carcinogenic (cancer-causing), but some of the other chemicals released by smoking are poisonous. These include tar, carbon monoxide, and cyanide. One known carcinogen, benzopyrene, found in both types of smoke, seems to be greater in marijuana smoke.
go to http://www.coolnurse.com/marijuana.htm
again here Im stupid, before I knew the truth about mj, now I smoke a lot of herb but not condoning it