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:
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)
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. 
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.
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):
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.
The toxicokinetics of opioid drugs varies within the class. Half lives range from minutes (heroin) to many hours (methadone). Potencies of opioids also vary drastically, with more potent synthetic drugs such as fentanyl, carfentanil and newer compounds causing overdose deaths and necessitating large doses of naloxone for reversal.
Opioids tend to be lipophilic and metabolized in the liver by both phase 1 (modification) and phase 2 (conjugation) reactions.
History and physical examination in patients with OUD vary depending on duration and intensity of use. Patients who sporadically misuse small doses of opioids may have a completely normal physical exam and no clear historical findings. Patients with chronic oral opioid use may have sedation if actively using the drug, along with miosis and hyperactive response to pain.
Patients who are dependent on intravenous heroin may have the many effects of injection drug abuse:
History may be limited as patients are often not forthcoming when discussing substance abuse patterns. However, it is crucial to obtain detailed history in patients in whom OUD or its sequelae are suspected.
Providers who suspect OUD should begin with a detailed history and physical exam. Patients may initially withhold information, or be overtly dishonest and manipulative, depending on reasons for seeking medical attention.
As mentioned above, these patients are at risk for secondary effects of drug abuse. Patients dependent on heroin frequently have infectious complications. Therefore, many patients should have laboratory studies ordered and selected imaging depending on presenting symptoms. 
Practitioners should offer patients who have OUD inpatient or outpatient substance use disorder (SUD) treatment. The short-term use of new opioid prescriptions does not provide long-term benefit. Regulations limiting prescription of opioids are increasingly incorporated into state laws in the US.
Patients presenting with opioid withdrawal often require antiemetic/antidiarrheal therapy and IV hydration. Medications for OUD (MOUD), such as Buprenorphine (a partial mu agonist and kappa antagonist), can be initiated for effective therapy in a medically supervised opioid withdrawal. Buprenorphine should be started in patients with mild-to-moderate withdrawal (Clinical Opioid Withdrawal Scale [COWS] of greater than 10 or 12) symptoms. Methadone, which is a full agonist mu receptor, can also control opioid withdrawal symptoms and complete opioid detoxification. 
Opioid overdose should be promptly treated with naloxone to reverse the effects of the drug, particularly respiratory depression. Adequate intravenous access allows IV fluid administration and repeat naloxone dosing when indicated. Begin with an intravenous dose of 0.4 to 0.8 mg to reverse neurologic and cardiorespiratory symptoms. Patients who have taken large doses of very potent opioids may require larger doses. Naloxone can also be administered intranasally and intramuscularly.
Medications have shown promising results in the treatment of OUD. Nalbumetone, buprenorphine, methadone, and naltrexone are used in various combinations to decrease abuse of both oral opioids and heroin. All patients at risk for overdose should have or receive naloxone kits for home use. 
OUD has reached epidemic proportions both in the US and worldwide. Forty-nine US states have enacted prescription drug monitoring programs.
Other preventive treatments include good samaritan laws and naloxone distribution for overdose death prevention, harsher penalties for drug dealers, disincentives to the prescription of opioids, needle-exchanges to curtail infectious complications, and increased state and federal funding for rehabilitation and recovery.
Opioids, also called narcotics, are highly addictive pain medications. While they are strong pain relievers, they have high addiction potential. It behooves clinicians to prescribe opioids only for severe pain and discontinue the medication as soon as feasible.
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