Incentive Salience and the Transition to Addiction

Most adults have used a potentially addictive drug at least once in their lifetime, if caffeine, alcohol, and nicotine are included in addition to illicit drugs. In some cases, contact with a substance is so frequent and socially accepted that many in society fail to recognize it as a “drug.” However, relatively few people develop sufficient problems with drug use to meet the formal criteria for addiction, even for potent illegal drugs such as cocaine or heroin. Drug addiction is characterized by compulsive drug seeking, an impairment of social and psychological functions and/or damage to one’s health. It typically involves overwhelming involvement with drug procurement and intake, a loss of control, and a narrowing of interests away from other forms of reward besides the drug of choice. According to a 2004 survey, less than 10% of the US population meet the criteria for alcohol abuse or any illegal drug abuse disorder, and an even smaller proportion suffer from chronic drug addiction. Yet, the worldwide monetary and social costs associated with drug control measures, corruption, lost productivity, and treatment of drug addiction are enormous. The chief problem in treating drug addiction is chronic or repeated relapse by those who have become addicted in the above sense. Even after prolonged periods of withdrawal and abstinence, a high percentage of addicted individuals in treatment programs eventually relapse to drug taking. For example, in the case of a study of heroin users, relapse rates to reuse after cessation were approximately 60% within 3 months and at least 75% within 12 months. For this reason, drug addiction is characterized as a chronic relapsing disorder; relapse is the rule rather than the exception and often occurs repeatedly. There are three reasons frequently suggested to explain relapse: (1) drug euphoria – that addicts resume drug taking to experience the intense pleasure