The condition in which a person's body relies on a given drug in order to function isthe condition in which a person's body relies on a given drug in order to function is

Answer: Drug dependence occurs when you need one or more drugs to function. The American Psychiatric Association (APA) used to distinguish between dependence and abuse. 

Substance dependence, also known as drug dependence, is a biopsychological situation whereby an individual's functionality is dependent on the necessitated re-consumption of a psychoactive substance because of an adaptive state that has developed within the individual from psychoactive substance consumption that results in the experience of withdrawal and that necessitates the re-consumption of the drug. A drug addiction, a distinct concept from substance dependence, is defined as compulsive, out-of-control drug use, despite negative consequences. An addictive drug is a drug which is both rewarding and reinforcing ,  a gene transcription factor, is now known to be a critical component and common factor in the development of virtually all forms of behavioral and drug addictions, but not dependence.