Dry-herb vaporizers can be used to inhale cannabis. Of the studies about vaporizing cannabis, few have addressed the quality of the vapor extracted and delivered; instead, studies usually focus on the mode of usage of the vaporizers. There are 483 identifiable chemical constituents known to exist in the cannabis plant, and at least 85 different cannabinoids have been isolated from the plant. The aromatic terpenoids begin to vaporize at , but the more bio-active tetrahydrocannabinol (THC), cannabidiol (CBD) and cannabinol (CBN) do not vaporize until near their respective boiling points: THC , CBD 160–180 °C (320–356 °F), and CBN .