Physiological considerations in opioid addiction

In the past two decades, there has been an alarming increase in prescriptions of opioids. Opioids provide a variety of actions in the body including analgesic effects, which are considered biological rewards that activate internal reward systems. The salience network helps a person pay attention to certain stimuli which leads to the activation of the reward system. The reward system is strongly stimulated by drugs of misuse, leading to a rewiring of brain circuitry and a shift to what stimulus the salience system deems important. Thus the use of certain drugs such as opioids, changes from a choice to a physical response because of reward of hedonistic effects. Over time, this results in long-lasting brain changes and the development of compulsive behaviors commonly known as addictive. Once an opioid use disorder is identified, practitioners have a chance to intervene and to help with the understanding of physiological and psychological factors driving addiction. Opioid agonist therapy has a pharmacologic basis to relieve not only withdrawal but also craving for the use of opioids. This chapter focuses on the physiological consequences of opioid use disorder and provides an understanding of the role of opioid agonist therapy as a treatment.