Tobacco has dramatic negative consequences for those who smoke it. In addition to its high addiction potential , tobacco is causally associated with over 400,000 deaths yearly in the United States, and has a significant negative effect on health in general . More specifically, over 140,000 lung-related deaths in 2001 were attributed to tobacco smoke . Comparable consequences would naturally be expected from cannabis smoking since the burning of plant material in the form of cigarettes generates a large variety of compounds that possess numerous biological activities .
While cannabis smoke has been implicated in respiratory dysfunction, including the conversion of respiratory cells to what appears to be a pre-cancerous state , it has not been causally linked with tobacco related cancers  such as lung, colon or rectal cancers. Recently, Hashibe et al  carried out an epidemiological analysis of marijuana smoking and cancer. A connection between marijuana smoking and lung or colorectal cancer was not observed. These conclusions are reinforced by the recent work of Tashkin and coworkers  who were unable to demonstrate a cannabis smoke and lung cancer link, despite clearly demonstrating cannabis smoke-induced cellular damage.
Furthermore, compounds found in cannabis have been shown to kill numerous cancer types including: lung cancer , breast and prostate , leukemia and lymphoma , glioma , skin cancer , and pheochromocytoma . The effects of cannabinoids are complex and sometimes contradicting, often exhibiting biphasic responses. For example, in contrast to the tumor killing properties mentioned above, low doses of THC may stimulate the growth of lung cancer cells in vitro .