BASIC NEUROBIOLOGY OF DRUG ABUSE
DEPENDENCE VERSUS ADDICTION
Recent neurobiologic research has led to the conceptual and mecha-nistic separation of “dependence” and “addiction.” The older term “physical dependence” is now denoted as dependence, whereas “psychological dependence” is more simply called addiction.
Every addictive drug causes its own characteristic spectrum of acute effects, but all have in common that they induce strong feelings of euphoria and reward. With repetitive exposure, addic-tive drugs induce adaptive changes such as tolerance (ie, escala-tion of dose to maintain effect). Once the abused drug is no longer available, signs of withdrawal become apparent. A combi-nation of such signs, referred to as the withdrawal syndrome, defines dependence. Dependence is not always a correlate of drug abuse—it can also occur with many classes of nonpsychoactive drugs, eg, sympathomimetic vasoconstrictors and bronchodila-tors, and organic nitrate vasodilators. Addiction, on the other hand, consists of compulsive, relapsing drug use despite negative consequences, at times triggered by cravings that occur in response to contextual cues (see Box: Animal Models in Addiction Research). Although dependence invariably occurs with chronic exposure, only a small percentage of subjects develop a habit, lose control, and become addicted. For example, very few patients who receive opioids as analgesics desire the drug after withdrawal. And only one person out of six becomes addicted within 10 years of first use of cocaine. Conversely, relapse is very common in addicts after a successful withdrawal when, by definition, they are no longer dependent.