"The use of a vaporizing device may mitigate some of these symptoms. Cannabis vaporization is a technique aimed at suppressing the formation of irritating respiratory toxins by heating cannabis to a temperature where active cannabinoids are volatilized, but below the point of combustion where smoke and associated toxins form. The use of a vaporizer is associated with higher plasma THC concentrations than smoking marijuana cigarettes, little if any carbon monoxide production, and significantly fewer triggered respiratory symptoms."

Source

American Medical Association, Council on Science and Public Health, "Report 3 of the Council on Science and Public Health: Use of Cannabis for Medicinal Purposes" (December 2009), p. 15.
http://drugwarfacts.org/cms/f…