One of the main health concerns for those who use or would like to use medical marijuana therapy is whether or not smoking marijuana can lead to adverse health effects. Because smoking contains carcinogens, carbon monoxides, and other toxins, people fear smoking marijuana could lead to complications like cancer in the head, neck, or lungs. Now, however, a systematic literature review published in the Archives of Oral Biology reports marijuana smoke exposure does not increase the risk of developing cancers in the head or neck.
Within the review, investigators from the Federal University of Minas Gerais in Brazil looked at nine case controlled studies to analyze the relationship between smoking marijuana and the development of these forms of cancer. They concluded those who used cannabis were not more likely to develop head or neck cancer than those with no history of the use. Another analysis of a portion of these studies published in the International Journal of Cancer also did not recognize a relationship between cannabis smoke and lung cancer. In fact, a case-controlled trial found in the journal Cancer Prevention Research found moderate use of marijuana actually reduced the risk for head and neck cancer.
You can take a look at the Daily Chronic's analysis of these reports here.