"findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use,"

"In summary, the accumulated weight of evidence implies far lower risks for pulmonary complications of even regular heavy use of marijuana compared to the grave pulmonary consequences of tobacco."

By greatly, I meant as bad as tobacco which dramatically increases the risk of lung cancer.

The previous poster was commenting on the health risks of tobacco being caused entirely by burning plant matter. However, the evidence suggests this isn't true.