in humans. One molecule, delta-9-tetrahydrocannabinol, or THC, has
been identified as the major psychoactive chemical constituent of
cannabis:
Ss OH
oO.
Delta-9-tetrahydrocannabinol (THC)THC was identified from cannabis only in 1964, relatively recently
given that so many other psychoactive molecules from plants were
identified in the nineteenth century.
THC is one of about sixty different chemically related molecules
found in cannabis. Collectively these molecules are called cannabi-
noids. They are not known to exist in any other variety of plant. Many
of the cannabinoids are undoubtedly physiologically active in varying
ways and to varying degrees and contribute to the many medicinally
useful effects of cannabis.
After the discovery of THC, another twenty-five years went by be-
fore the site of action of THC in the nervous system was revealed. THC
is a very hydrophobic molecule and easily sticks to lipids and dissolves
into phospholipid bilayer membranes. This prompted speculation
that perhaps the primary mechanism of action of THC in the brain
involves dissolving into lipid membranes of neurons and somehow
disrupting the cell’s normal function. However, work during the
1980s suggested that THC interacted with a specific receptor, and by
1990 the cannabinoid (CB) receptor was identified. Like many neuro-