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Drug addiction: the neurobiology of behaviour gone awry
Nora D. Volkow and Ting-Kai Li
Abstract | Drug addiction manifests as a compulsive drive to take a drug despite serious adverse consequences. This aberrant behaviour has traditionally been viewed as bad choices that are made voluntarily by the addict. However, recent studies have shown that repeated drug use leads to long-lasting changes in the brain that undermine voluntary control. This, combined with new knowledge of how environmental, genetic and developmental factors contribute to addiction, should bring about changes in our approach to the prevention and treatment of addiction.
Drugs, both legal (for example, alcohol and nicotine) and illegal (such as cocaine, meth-amphetamine, heroin and marijuana) are misused for various reasons, including for pleasurable effects, the alteration of mental state, to improve performance and, in certain instances, for self-medication of a mental disorder. Repeated drug use can result in addiction, which is manifested as an intense desire for the drug with an impaired ability to control the urges to take that drug, even at the expense of serious adverse consequences. To avoid confusion with physical dependence, the term drug addiction is used here instead of drug dependence, which is the clinical term favoured by the Diagnostic and Statistical Manual of Mental Disorders (fourth edition; DSM-IV). Physical dependence results in withdrawal symptoms when drugs, such as alcohol and heroin, are discontinued, but the adaptations that are responsible for these effects are different from those that underlie addiction.
The aberrant behavioural manifestations that occur during addiction have been viewed by many as choices of the addicted individual, but recent imaging studies have revealed an underlying disruption to brain regions that are important for the normal processes of motivation, reward and inhibitory control in addicted individuals1.This provides the basis for a different view: that drug addiction is a disease of the brain, and the associated abnormal behaviour is the result of dysfunction of brain tissue, just as cardiac insufficiency is a disease of the heart and abnormal blood circulation is the result of dysfunction of myocardial tissue2 (FIG. 1).
Therefore, although initial drug experimentation and recreational use might be volitional, once addiction develops this control is markedly disrupted. Although imaging studies consistently show specific abnormalities in the brain function...