Misuse and abuse of prescription opioid analgesics and use of recreational opioids such as heroin creates strong addiction patterns. The Drug Abuse Warning Network (DAWN) claims an increase of over 100% in emergency room visits from opioid analgesic abuse from 1994 to 2001 and heroin addiction rates have risen to nearly 1,000,000 in the United States. These addiction issues damage the health of addicts and cost the health care systems a large sum of money. To find effective treatment venues for opioid addiction, researchers have explored the neurological changes caused by chronic use of opioids. Structural changes take place in key brain areas linked to addiction, such as the ventral tegmental area (VTA), amygdala, and the nucleus accumbens. To further understand the mechanism of these structural changes, scientists currently research the expression or lack of expression of certain receptors. These receptors appear crucial the tolerance and addiction in opioid use, especially mu and kappa opioid receptors on cranial neurons. All of these mechanisms will be discussed in effort to explain the neuroplasticity that occurs in opioid addiction.