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TABLE 1.5 Cannabinoids Identified in Marijuana
Cannabinoid	Common	No. of Known
Group	Abbreviation	Variants in Each Group
D9-Tetrahydrocannabinol	D9-THC	9
D8-Tetrahydrocannabinol	D8-THC	2
Cannabichromene	CBC	5
Cannabicyclol	CBL	3
Cannabidiol	CBD	7
Cannabielsoin	CBE	5
Cannabigerol	CBG	6
Cannabinidiol	CBND	2
Cannabinol	CBN	7
Cannabitriol	CBT	9
Miscellaneous types		11
Total		66

groups of closely related cannabinoids, many of which differ by only a single chemical moiety and might be midpoints along biochemical path—ways-that is, degradation products, precursors, or byproducts.16^,18 D⁹ -tetrahydrocannabinol (D⁹-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 D⁹-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