Cannabis smoke contains thousands of organic and inorganic chemical compounds. This tar is chemically similar to that found in tobacco smoke,  and over fifty known carcinogens have been identified in cannabis smoke,  including; nitrosamines, reactive aldehydes, and polycylic hydrocarbons, including benz[a]pyrene.  Light and moderate use of cannabis is not believed to increase risk of lung or upper airway cancer. Evidence for causing these cancers is mixed concerning heavy, long-term use. In general there are far lower risks of pulmonary complications for regular cannabis smokers when compared with those of tobacco.  Combustion products are not present when using a vaporizer , consuming THC in pill form, or consuming cannabis edibles .