Tetrahydrocannabinol (THC), in full (−)-trans-Δ9-tetrahydrocannabinol, is the cannabinoid that mainly produces the psychotropic effects of cannabis. The living plant holds little of it. The glandular trichomes of the female flowers make its carboxylic acid, tetrahydrocannabinolic acid (THCA). THC forms from the acid without the help of an enzyme as the harvested material dries, is stored or is smoked.
The balance between THC and cannabidiol (CBD) in a plant is inherited almost as a single gene and defines its chemotype. It differs widely between the landraces of different regions. In a study of 157 accessions grown together, the allele for THC production was fixed in the narrow-leaflet drug landraces and rare in the hemp and ruderal populations of Europe and Central Asia.
The structure of THC was established in 1964 by Y. Gaoni and Raphael Mechoulam, who isolated it from hashish. Its content in the dried flowering tops of female plants is the measure by which many countries separate hemp from drug cannabis, at a threshold of 0.3 per cent taken from a taxonomy of the genus published in 1976. read more →
