The dictionary defines a medicine as a drug that is used to treat diseases, or to relieve pain. This term includes materials that act upon various tissues, organs and systems of the anatomy. Upon further inquiry one finds that the term narcotic refers to those preparations which produce profound sleep, lethargy, and relief of pain. This article will deal primarily with the sensation called pain, and the use of narcotics to relieve that sensation.
Ralph K. Davies, Nature and Effects of Narcotics for Pain, 13 Clev.-Marshall L. Rev. 490 (1964)