ABSTRACT
A notable aspect of a wide variety of potent pharmacological agents is that of tolerance. Tolerance is defined as the change of effectiveness of a drug "so that an increased amount of drug is required to produce the same specified degree of effect, or less effect is produced by the same dose of drug" (Kalant, LeBlanc & Gibbins, 1971, p. 137). One class of drugs in which tolerance is a very potent phenomenon, and for which there is a long history of research, is the opiates, including morphine.
