The pharmacology of mood-altering drugs of abuse.

The majority of mood-altering drugs that have significant abuse potential possess several properties that contribute to drug dependence, including behavioral reinforcing and rewarding actions, tolerance to behavioral effects, and development of physical dependence. Although various drug classes may differ in the relative importance of these properties, it is generally recognized that they form the basis of abuse and misuse of many drugs. These phenomena are not the result of novel or unique drug actions but represent biochemical or neurochemical modulation of normal functional mechanisms in the central nervous system.