The pathogenesis of addiction involves a series of complex interactions between biological (e.g., genetic vulnerability, gender, physiological and behavioral response to drug experimentation and use, drug-induced alterations in gene expression and resultant proteins), environmental (e.g., legality, acceptability, availability), psychological (e.g., novelty seeking or harm avoidance, personality traits), and drug factors (e.g., dose, pattern of use, and route of administration). The voluntary initiation and continuation of a behavior that is harmful to health is an important aspect of the etiology of many common diseases, including cardiovascular disease and metabolic syndrome. However, in addictions, the role of volition in initiation and later drug-induced impairments in judgment are most salient. Moreover, licit and illicit drug use is typically initiated in childhood, when the ability to balance the apparent short-term benefits of experimentation and use with the addictive potential and long-term physical and mental consequences of dependence is generally lacking. Very few adults initiate drug use voluntarily if they have remained drug naïve into adulthood, and tobacco and alcohol industries specifically target youth to recruit new users for this reason. However, abuse and addiction
