Opioid use disorder and opioid addiction remain at epidemic levels in the US and worldwide. Three million US citizens and 16 million individuals worldwide have had or currently suffer from opioid use disorder (OUD). More than 500,000 in the United States are dependent on heroin. The diagnosis of OUD is made by meeting two or more of the eleven criteria in a year time period. 

Key elements are as follows:

• Increasing dose/tolerance
• Wish to cut down on use
• Excessive time spent to obtain or use the medication
• Strong desire to use
• Use interferes with obligations
• Continued use despite life disruption
• Use of opioid in physically hazardous situations
• Reduction or elimination of important activities due to use
• Continued use despite physical or psychological problems
• Need for increased doses of the drug
• Withdrawal when dose is decreased

The increase in OUD can be partially attributed to overprescribing of opioid medications. Healthcare providers in the 1990s increased opioid prescribing in response to: the "pain as fifth vital sign" campaign, downplay of the abuse potential of opioids, and aggressive marketing of drugs such as Oxycontin and Opana. Risk factors for misuse of these medications are initiation at young age, previous history of illicit drug or alcohol abuse, family history of illicit drug or alcohol abuse, sexual abuse in females, adverse childhood experiences, and psycological comorbidities (depression, bipolar disorder and attention deficit hyper activity disorder)[1]

Opioid addiction results from many practices and behaviors. The United States possesses an insatiable appetite for prescription of opioid medications. In 2015, 91.8 million individuals in the United States used prescription opioids. Due to inarguable abuse potential, these drugs are frequently misused, with high numbers of patients developing dependence. Opioid medications prescribed for mild to moderate acute pain were continued indefinitely, with no intention of tapering or ceasing use. Due to pharmacologic effects, opioids are highly addictive. Tolerance is achieved within days, and the withdrawal syndrome is severe. [2][3][4][2]

Opioid addiction afflicts individuals from all socioeconomic and educational backgrounds. Four million people admit to the nonmedical use of prescription opioids. Perhaps more concerning, 400,000 people had used heroin in the past month based on data from 2015 through 2016. Roughly 80% of new heroin users in the United States report pills as their initiation to opioid use and subsequent OUD.

From 2002 through 2011, approximately 25 million people in the United States began nonmedical use of pain relievers. More than 11 million misused the medications.

Emergency department visits due to complications and overdose have increased annually since 2010. Rates of ED visits involving opioids more than tripled from 1999 through 2013. 

In 2017, opioid overdose was declared a national emergency in the United States. [5][6]

Opioids bind to receptors in the central and peripheral nervous systems (primarily delta, kappa, and mu), with treatment effects for pain, cough, and diarrhea. Action on these same receptors induces intense euphoria. This causes many individuals to continue use with the intention of recreating that first high. Most people who misuse opioids do so for pain relief or to prevent withdrawal symptoms. Increasing evidence is dispelling the myth that opioids are effective long-term analgesic medications.

Below are receptors matched to physiologic effects in the central nervous system (nociceptin and zeta receptors are increasingly researched):

• Delta: analgesia, antidepressant, convulsant, physical dependence, modulate mu-related respiratory depression
• Kappa: analgesia, anticonvulsant, depression, hallucination, diuresis, dysphoria, miosis, neuroprotection, sedation
• Mu: analgesia, physical dependence, respiratory depression, miosis, euphoria, reduced GI motility, vasodilation. Peripheral mu receptors are tissue-specific with higher concentrations in bronchial smooth muscle and the digestive tract. This is the reason for opioids suppressing the cough reflex and causing constipation.[7]

Withdrawal symptoms manifest when opioids are discontinued abruptly, though can occur with tapered cessation of medications. Withdrawal symptoms present in acute, subacute, and chronic phases. Most healthcare providers are aware of the acute withdrawal symptoms: hot/cold flashes, nausea, vomiting, diarrhea,sweating, lacrimation, insomnia, anxiety, generalized muscle pain, tachycardia,piloerection, dehydration. However many providers do not have experience with the prolonged subacute chronic phases.

Chronic opioid use causes alterations in receptor sensitivity, leading to medication tolerance and changes in pain perception. Opioid induced hyperalgesia (OIH) causes pain perception out of proportion to stimulus (hyperalgesia) in those who use or misuse opioids long-term.