Drug addiction is a pathological condition. The disorder of addiction involves the progression of acute drug use to the development of drug-seeking behavior, the vulnerability to relapse, and the decreased, slowed ability to respond to naturally rewarding stimuli. The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) has categorized three stages of addiction: preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect. These stages are characterized, respectively, everywhere by constant cravings and preoccupation with obtaining the substance; using more of the substance than necessary to experience the intoxicating effects; and experiencing tolerance, withdrawal symptoms, and decreased motivation for normal life activities.[2] By the American Society of Addiction Medicine definition, drug addiction differs from drug dependence and drug tolerance.[3]
http://en.wikipedia.org/wiki/Drug_addiction

The Center for Substance Abuse Treatment (CSAT) is an agency of the United States government. It is a part of the Substance Abuse and Mental Health Services Administration (SAMHSA), within the U.S. Department of Health and Human Services (DHHS). CSAT was established in October 1992 with a Congressional mandate to expand the availability of effective treatment and recovery services for alcohol and drug problems. CSAT supports a variety of activities aimed at fulfilling its mission:

• To improve the lives of individuals and families affected by alcohol and drug abuse by ensuring access to clinically sound, cost-effective addiction treatment that reduces the health and social costs to our communities and the nation.

CSAT works with States and community-based groups to improve and expand existing substance abuse treatment services under the Substance Abuse Prevention and Treatment Block Grant Program. CSAT also supports SAMHSA’s free treatment referral service to link people with the community-based substance abuse services they need. Because no single treatment approach is effective for all persons, CSAT supports the nation's effort to provide multiple treatment modalities, evaluate treatment effectiveness, and use evaluation results to enhance treatment and recovery approaches.

http://en.wikipedia.org/wiki/Center_for_Substance_Abuse_Treatment