Narcotics Anonymous (NA), founded in 1953, describes itself as a "nonprofit fellowship or society of men and women for whom drugs had become a major problem." Narcotics Anonymous uses a 12-step model developed for people with varied substance use disorders and is the second-largest 12-step organization.As of May 2018 there were more than 70,000 NA meetings in 144 countries.

Substance dependence, also known as drug dependence, is a biopsychological situation where-by 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, which results in the experience of withdrawal, which 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. ΔFosB, 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.

The International Classification of Diseases classifies substance dependence as a mental and behavioural disorder.

Within the framework of the 4th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), substance dependence is redefined as a drug addiction, and can be diagnosed without the occurrence of a withdrawal syndrome. It was described accordingly: "When an individual persists in use of alcohol or other drugs despite problems related to use of the substance, substance dependence may be diagnosed. Compulsive and repetitive use may result in tolerance to the effect of the drug and withdrawal symptoms when use is reduced or stopped. This, along with Substance Abuse are considered Substance Use Disorders." In the DSM-5 (released in 2013), substance abuse and substance dependence have been merged into the category of substance use disorders and they no longer exist as individual diagnoses.