Marijuana is the common name for Cannabis sativa,
a hemp plant that
grows throughout temperate and tropical climates. The most recent review of the constituents of
marijuana lists 66 cannabinoids (Table 1.5).16 But that
does not mean there
are
66
different cannabinoid effects or interactions. Most of the cannabinoids are closely related;
they fall
into only 10 groups of closely related cannabinoids, many of
which differ by only a single chemical moiety and might be midpoints along biochemical pathways--that
is,
degradation products, precursors, or byproducts.16,18 9-tetrahydrocannabinol (
9- THC)
is
the primary psychoactive ingredient; depending on the particular plant, either THC or
cannabidiol is the most abundant cannabinoid in marijuana (Figure 1.1). Throughout this
report, THC is used to indicate 9-THC. In the few cases where variants of THC are discussed, the full names are used. All the cannabinoids are lipophilic--they are highly soluble in fatty fluids and tissues but not in water.
Indeed, THC is so lipophilic that it is aptly described as "greasy."
Throughout this report, marijuana refers to unpurified plant extracts, including leaves and flower tops, regardless of how they are consumed--whether by ingestion or by smoking. References to the effects of marijuana should be understood to include the
composite effects of its various components; that
is,
the effects of THC are included
among the effects of marijuana, but not all the effects of marijuana are necessarily due to THC. Discussions concerning cannabinoids refer
only
to those particular compounds and not
to the plant extract. This distinction is important; it is often blurred or exaggerated.
Cannabinoids are produced in epidermal glands on the leaves (especially the upper
ones), stems, and the bracts that
support the flowers of the marijuana plant.
Although the flower itself has no epidermal glands, it has the highest cannabinoid content anywhere on
the
plant, probably because of the accumulation of
resin secreted by the supporting
bracteole (the small leaf-like part below the flower). The amounts of
cannabinoids and their relative abundance in a marijuana plant vary with growing conditions, including
humidity, temperature, and soil nutrients (reviewed in Pate, 199414). The chemical
stability of cannabinoids in harvested plant material is also affected by moisture, temperature, sunlight, and storage. They degrade under any storage condition.
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