Substance use disorders (SUD) comprise a clinically heterogeneous group of conditions. In part this heterogeneity is due to difficulties in defining the disorder consequent to drug use. Apart from the involvement of criteria other than medical (e.g., legal, cultural) in defining the normative drug-pertaining behavior, the SUD phenotype has not been uniformly described, and there has been disagreement as to what it should be labeled, e.g., dependence or addiction (O'Brien et al., 2006). Whereas dependence is accepted in the current classification (DSM, ICD), as based on physiological drug response, addiction, defined as compulsive drug-seeking and use, may be more relevant to the designation of the overall clinically important phenotype. Dependence is a normal physiological adaptation to drug action, which may occur outside of drug abuse context (e.g., during pain treatment); it is addiction, a pernicious behavior, that results in health and other ensuing problems. This behavior frequently, but not necessarily, results from or is contributed by dependence, whereas dependence does not necessarily manifest in addictive behavior.
