See Addiction.

an addiction to a drug (especially a narcotic drug)

a chronic relapsing disorder characterized by compulsive, often uncontrollable, drug seeking and drug use in the face of negative consequences

an extreme state of addiction resulting from drug abuse

A monopolization of the attentional system by drug-related stimuli. For example, if cocaine addicts see white powder, they will probably experience cravings, because their brain associates white powder with cocaine.

The continued compulsive use of drugs in spite of adverse health or social consequences.

Drug addiction is a condition where a person takes a drug compulsively, despite potential harm to themselves, or their desire to stop. Although being addicted implies dependence, it is possible to be dependent on a drug without being addicted. People who take drugs to treat diseases and disorders, which interfere with their ability to function, may experience improvement of their condition.