The age of first use, route of administration and individual response to drug user are all factors that influence the likelihood of initial drug use progressing through regular use to dependence. Continued use leads to physiological and neurobiological changes that in turn lead to physical dependence manifested as withdrawal on cessation of use, and ongoing craving predisposing to resumption of drug use (Koob & Volkow, 2010).
Dependent drug users tend to show greater impulsiveness; make choices based on immediate benefit, with little regard to long term negative consequences; and show poor impulse control, arising from a lack of activity in the area of the brain responsible for “executive function”. Factors that affect the “executive” area of brain function (such as planning, problem-solving and interpreting risk) include:
• characteristics of the person (genetics, early experiences)
• stage of brain maturation (this is one of the last areas of the brain to complete development, at around 25 years of age; consequently adolescents are more vulnerable to the development of problematic drug use) and
• brain damage, due to injury or neurotoxicity of drug use.
Drugs are thought to act through systems in the brain that have their origin in responses to stimuli that are relevant to preservation of the species food, sex, fight and flight behaviour). In drug addiction, drug-seeking becomes the focus at the expense of natural rewards. The continual activation of the structures in the brain by drug use causes changes in neuronal systems that “hard-wire” the memory of drug use as a source of “reward” and necessary for survival. It is this in-built memory that makes addicts vulnerable to long-term relapse (meaning a return to problematic drug use) and is the basis of the chronic relapsing nature of drug dependence (Koob & Volkow, 2010).