Drug addiction is a chronic psychiatric disorder characterized by the persistent, compulsive, and uncontrolled use of a drug despite harmful consequences. Scientific studies on addictive behaviors began in the 1930s and revealed that people with an addiction are not simply lacking in willpower; instead, they are unable to control their use of the drug (135). With advances in our understanding of the effects of alcohol, nicotine, and illicit drugs on brain physiology and behavior, it has become evident that addiction is a psychiatric disease attributable to biological and environmental factors (135). The development of addiction involves several steps: the initiation of substance use, the transition from experimental use to regular use, and the actual development of addiction. Environmental factors such as peer pressure, parental monitoring, and the accessibility of a substance play a major role in the initial decision to drink, smoke, or take illicit drugs. Beyond the initiation step, the transition from regular substance use to dependence differs from person to person and is largely under genetic control (Figure 1) (74, 133, 135).
