Tetrahydrocannabinol, or THC, is a chemical found in the HEMP plant, CANNABIS SATIVA, that causes the PSYCHOACTIVE effects in MARIJUANA, BHANG, HASHISH, and GANJA. Hashish is derived from the resin that oozes from the flowering tips of the female plant; bhang comes from the dried leaves and flowering shoots of the female plant; and ganja comes from small leaves. THC is one of the three natural cannabinoids—chemical constituents of Cannabis—the other two being cannabinol (CBN) and cannabidiol (CBD).

As of 2000, marijuana is the most commonly used nonlegal drug in the United States. Its usage peaked during the late 1970s, when about 60 percent of high school seniors reported having tried marijuana, with 11 percent reporting daily use. Usage has declined since 1979; as of 1999, 2 to 3 percent of the 70 million Americans who had tried cannabis described themselves as daily users.

Pharmacological Effects

For more than 30 years, the discovery...