From Who Falls to Addiction, and Who Is Unscathed? by Richard A. Friedman, M.D.
Alcohol and drugs affect mood and behavior by activating the same brain circuits that are disrupted in major psychiatric illnesses.
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Dr. Nora Volkow, director of the National Institute on Drug Abuse, has shown in several brain-imaging studies that people addicted to such drugs as cocaine, heroin and alcohol have fewer dopamine receptors in the brain's reward pathways than nonaddicts ... When Dr. Volkow compared the responses of addicts and normal controls with and infusion of a stimulant, she discovered that controls with high numbers of D2 receptors, a subtype of dopamine receptors, found it aversive, while addicts with low receptor levels found it pleasurable. This finding and others like it suggest that drug addicts may have blunted reward systems in the brain, and that for them everyday pleasures don't come close to the powerful reward of drugs.
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