Alcohol and drug dependence: brain mechanisms and behavioral impact.

Substance use disorders follow a dynamic course, which involves cycles of development, maintenance, recovery, and relapse. Dependence on alcohol and drugs develop from chronic use of selective substances that react with, displace, supplant, or alter essential endogenous brain chemistry, and dependence evolves as the exogenous substance is required to replace the dysfunctional endogenous process (Koob and Le Moal 2005). Because addiction has such a firm biological basis, simple removal of the addicting substance can itself be dangerous and cause life-threatening withdrawal effects. The alterations caused by addictive substances are now known to result in structural and functional changes in selective brain systems, depending on the substance. Although improvement in the condition of brain structure and function can occur with abstinence, even safe withdrawal from the substance does not ensure full recovery to all individuals every time they withdraw, the withdrawal process itself may be harmful, and withdrawal does not ensure lifelong sobriety. The problems associated with alcohol and drug addiction are enormous financially and result in untold personal and family strife. It is estimated that approximately 5% of the U.S. adult population is alcohol abusing or alcohol dependent. Although men are more likely to have an alcohol use disorder than women, the prevalence of alcohol-related disorders has increased over the past 10 years, particularly among women and people in the 30 to 65 year range (Grant et al. 2004). Use of illicit substances is also substantial. The National Survey on Drug Use and Health (NSDUH) estimates that in addition to the 15.4 million Americans aged 12 years or older with an alcohol use disorder in 2005, 3.3 million Americans abused or were dependent on both alcohol and an illicit drug, and 3.6 million abused or were dependent on illicit drugs other than alcohol. Of those addicted, only 10% receive any form of treatment. Heightened awareness, improved diagnosis, and reduction of societal stigma would likely reveal that the number of individuals addicted and needing treatment is even higher, the compromise of brain systems more widespread, and the toll on family and community even greater. Multi-front approaches have been resoundingly successful in educating public and family service providers in the diagnosis and treatment of other erstwhile “closet” conditions, such as Alzheimer’s disease, Parkinson’s disease, and autism. Behavior altering agents have been used by humans for at least fourmillennia. Reasons for engaging in substance-induced “mind-altering” experience range from religious to therapeutic to exploratory. Societal disdain of imbibing such substances has had many reasons but commonly has focused on disturbance the imbiber causes—often without personal awareness—to the public and the drain on societal resources resulting from impaired function and productivity. Thus, the “neuropsychological eye” of society recognized cognitive and motor impairment on activities of daily living in the acute drug or alcohol user and even noted the long-term consequences on performance in the chronic substance abuser. Yet, society has seldom looked kindly on “alcoholics” or “drug addicts,” imbuing stigma, discrimination, and a “boot-strap” approach to treatment. Perhaps the grandest scheme ever implemented to eradicate alcohol dependence, Prohibition, considered the “Noble Experiment,” was a decided failure. Neuropsychol Rev (2007) 17:235–238 DOI 10.1007/s11065-007-9039-5