According to Wikipedia, Drug addiction is a pathological condition which arises due to frequent drug use. 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.

Anyone that would like to add their own comments to this definition are invited, since the real toll of addiction is the personal suffering that happens at the individual and family level where addiction is more than a clinical problem, it occupies their entire lives.