Endogenous and Exogenous Opioids: Role in Substance Use Disorders.

Opioid use disorders have become an epidemic in recent years with rates nearly quadrupling since 1999 according to the US Centers for Disease Control and Prevention (Centers for Disease Control, Wide-ranging online data for epidemiologic research (WONDER). CDC, National Center for Health Statistics, Atlanta. Retrieved December 19, 2017, from http://wonder.cdc.gov, 2016). To understand substance use disorder (SUD) as a disease, many aspects must be studied including the circuitry in the brain, adaptations to neuronal circuitry and neurotransmitters, genetic variations increasing the risk for SUD, and treatments available for SUD. The mechanism in which an exogenous opioid may cause SUD is nearly identical to the mechanism of an endogenous opioid. This chapter reviews the clinical and epidemiological aspects of opioid use disorder, as well as the interactions between endogenous and exogenous opioids. Additionally, this chapter discusses current scientific data regarding genetic variations and mechanisms within brain circuitry and the role of endogenous opioids in substance use disorders generally (and opioid use disorder specifically). Future applications of these data to treatment of substance use disorders are also discussed.