What is a drug?

         I sleep in Greek means "narc" and the English coming from "narcotic" drugs as the last word, which is characteristic numbing, numbing, does not mean that makes it.
The concept of drug substance, usually refers to substances capable of numbing. However, an exhilarating, incite, soothe, alertness, which is used in some materials.

Drug substances affecting the central nervous system that disrupts the person using the mental and physical balance, this person leads to physical and psychological dependence; personal and social aspects of economic and social collapse forming substances.