Cannabis contains a number of chemicals referred to as cannabinoids. The cannabinoid D9-tetrahydrocannabinol (THC) is generally considered to be the most active chemical of cannabis, but other cannabinoids may also have therapeutic properties and/or affect the activity of THC. THC, cannabidiol (CBD) and other cannabinoids dissolve only in fats or fat-like materials. Cannabinoids are weak acids in the fresh plant, but are converted to their neutral form when they are aged, dried and heated. In their acid forms, cannabinoids have minimal psychological and medical effects; they become much more active after conversion to neutral forms.

More than 400 chemical compounds have been identified in the species Cannabis sativa, of which more than 60 are cannabinoids. Cannabinoids are unique to the cannabis plant. (The only other member of the Cannabaceae family, to which cannabis belongs, is hops, which does not contain any cannabinoids.)

The pharmacology of many of the cannabinoids is unknown, but the psychoactive properties of cannabis are attributed to THC. The pharmacology of THC has been studied in detail.

Shown here is the chemical structure for the cannabinoid D9-tetrahydrocannabinol (THC);

THC affects the human body through two different receptors. Receptors are structures located on brain cells and other tissues that are activated by only certain kinds of molecules. The CB1 receptor is located in the brain where THC produces its psychoactive effects. The CB2 receptor is primarily located in the immune system, but its role there is unclear. These receptors are naturally activated by the chemical anandamide, which is produced by the human body and has a similar but weaker effect than THC.^[1]

CBD does not itself have a psychoactive effect on the brain but does appear to affect how the brain synthesizes THC. In some studies CBD seemed to reduce the euphoria of THC,^[2,3] but in others it appeared only to delay the effect and might have even lengthened its duration.^[4,5]

References used above

1.          Joy, J.E. et al., Editors, "Marijuana and Medicine: Assessing the Science Base", Table 1.5, Institute of Medicine (1999) Karniol

2.          IG, Shirakawa I, Kasinski N, Pfeferman A, Carlini EA. "Cannabidiol interferes with the effects of delta-9-tetrahydrocannbinol in man". European Journal of Pharmacology 1975; 28:172-177.

3.          Zuardi AW, Shirakawa I, Finkelfarb E, Karniol IG. "Action of cannabidiol on the anxiety and other effects produced by delta 9-THC in normal subjects". Psychopharmacology (Berl) 1982; 76:245-250.

4.          Bird KD, Boleyn T, Chesher GB, Jackson DM, Starmer GA, Teo RKC. "Inter-cannabinoid and cannabinoid-ethanol interactions and their effects on human performance". Psychopharmacology 1980; 71:181-188.

5.          Hollister LE, Gillespie BA. "Interactions in man of delta-9-THC. II. Cannabinol and cannabidiol". Clinical Pharmacology and Therapeutics 1975; 18:80-83.