Drug addiction is a chronically relapsing disorder characterized by (i) compulsion to seek and take the drug, (ii) loss of control in limiting intake, and (iii) emergence of a negative emotional state (e.g., dysphoria, anxiety, irritability) reflecting a motivational withdrawal syndrome when access to the drug is prevented (defined here as dependence) (Koob and Le Moal, 1997). Addiction is assumed to be identical to the syndrome of Substance Dependence (as currently defined by the Diagnostic and Statistical Manual of Mental Disorders; American Psychiatric Association, 1994). Clinically and in animal models, the occasional but limited use of a drug with the potential for abuse or dependence is distinct from escalated drug intake and the emergence of a chronic drug-dependent state.
