Opioid use disorder

Source: Wikipedia, the free encyclopedia.

Opioid use disorder
Other namesOpioid addiction,
MedicationBuprenorphine, methadone, naltrexone[7][10]
Frequency16 million[11]
Deaths120,000[11]

Opioid use disorder (OUD) is a

dependence are important components of opioid use disorder.[13]

Risk factors include a history of opioid misuse, current opioid misuse, young age, socioeconomic status, race, untreated psychiatric disorders, and environments that promote misuse (social, family, professional, etc.).[14][15] Complications may include opioid overdose, suicide, HIV/AIDS, hepatitis C, and problems meeting social or professional responsibilities.[5][4] Diagnosis may be based on criteria by the American Psychiatric Association in the DSM-5.[4]

Opioids include substances such as heroin, morphine, fentanyl, codeine, dihydrocodeine, oxycodone, and hydrocodone.[5][6] A useful standard for the relative strength of different opioids is morphine milligram equivalents (MME).[16] It is recommended for clinicians to refer to daily MMEs when prescribing opioids to decrease the risk of misuse and adverse effects.[17]

Long-term opioid use occurs in about 4% of people following their use for trauma or surgery-related pain.[18] In the United States, most heroin users begin by using prescription opioids that may also be bought illegally.[19][20]

People with an opioid use disorder are often treated with

opioid replacement therapy using methadone or buprenorphine.[21] Such treatment reduces the risk of death.[21] Additionally, they may benefit from cognitive behavioral therapy, other forms of support from mental health professionals such as individual or group therapy, twelve-step programs, and other peer support programs.[22] The medication naltrexone may also be useful to prevent relapse.[10][8] Naloxone is useful for treating an opioid overdose and giving those at risk naloxone to take home is beneficial.[23] In 2020, the CDC estimated that nearly 3 million people in the U.S. were living with OUD and more than 65,000 people died by opioid overdose, of whom more than 15,000 were heroin overdoses.[24][25]

Diagnosis

The DSM-5 guidelines for the diagnosis of opioid use disorder require that the individual has a significant impairment or distress related to opioid uses.[4] To make the diagnosis two or more of 11 criteria must be present in a given year:[4]

  1. More opioids are taken than intended
  2. The individual is unable to decrease the number of opioids used
  3. Large amounts of time are spent trying to obtain opioids, use opioids, or recover from taking them
  4. The individual has cravings for opioids
  5. Difficulty fulfilling professional duties at work or school
  6. Continued use of opioids leading to social and interpersonal consequences
  7. Decreased social or recreational activities
  8. Using opioids despite being in physically dangerous settings
  9. Continued use despite opioids worsening physical or psychological health (i.e. depression, constipation)
  10. Tolerance
  11. Withdrawal

The severity can be classified as mild, moderate, or severe based on the number of criteria present.

dependence are components of a substance use disorder; addiction is the more severe form.[13]

Signs and symptoms

Opioid intoxication

Signs and symptoms of

Opioid overdose

US penny
is 19 mm (0.75 in) wide.

Signs and symptoms of opioid overdose include, but are not limited to:[28]

Withdrawal

Opioid withdrawal can occur with a sudden decrease in, or cessation of, opioids after prolonged use.[29][30] Onset of withdrawal depends on the half-life of the opioid that was used last.[31] With heroin this typically occurs five hours after use; with methadone, it may take two days.[31] The length of time that major symptoms occur also depends on the opioid used.[31] For heroin withdrawal, symptoms are typically greatest at two to four days and can last up to two weeks.[32][31] Less significant symptoms may remain for an even longer period, in which case the withdrawal is known as post-acute-withdrawal syndrome.[31]

Treatment of withdrawal may include methadone and buprenorphine. Medications for nausea or diarrhea may also be used.[30]

Cause

Opioid use disorder can develop as a result of

self-medication.[33] Scoring systems have been derived to assess the likelihood of opiate addiction in chronic pain patients.[34] Healthcare practitioners have long been aware that despite the effective use of opioids for managing pain, empirical evidence supporting long-term opioid use is minimal.[35][36][37][38][39] Many studies of patients with chronic pain have failed to show any sustained improvement in their pain or ability to function with long-term opioid use.[36][40][41][42][39]

According to position papers on the treatment of opioid dependence published by the United Nations Office on Drugs and Crime and the World Health Organization, care providers should not treat opioid use disorder as the result of a weak moral character or will but as a medical condition.[15][43][44] Some evidence suggests the possibility that opioid use disorders occur due to genetic or other chemical mechanisms that may be difficult to identify or change, such as dysregulation of brain circuitry involving reward and volition. But the exact mechanisms involved are unclear, leading to debate over the influence of biology and free will.[45][46]

Mechanism

Addiction

brain disorder characterized by compulsive drug use despite adverse consequences.[13][47][48][49] Addiction involves the overstimulation of the brain's mesocorticolimbic reward circuit (reward system), essential for motivating behaviors linked to survival and reproductive fitness, like seeking food and sex.[50] This reward system encourages associative learning and goal-directed behavior. In addiction, substances overactivate this circuit, causing compulsive behavior due to changes in brain synapses.[51]

The incentive-sensitization theory differentiates between "wanting" (driven by dopamine in the reward circuit) and "liking" (related to brain pleasure centers).[52] This explains the addictive potential of non-pleasurable substances and the persistence of opioid addiction despite tolerance to their euphoric effects. Addiction surpasses mere avoidance of withdrawal, involving cues and stress that reactivate reward-driven behaviors.[50] This is an important reason detoxification alone is unsuccessful 90% of the time.[53][54][55]

Mesocorticolimbic circuit
which plays major role in addiction that is affected by opioids

Overexpression of the

GABA-based projections to the ventral tegmental area (VTA) from the rostromedial tegmental nucleus (RMTg), which negatively modulate dopamine neurotransmission.[60][61] In other words, opioids inhibit the projections from the RMTg to the VTA, which in turn disinhibits the dopaminergic pathways that project from the VTA to the nucleus accumbens and elsewhere in the brain.[60][61]

The differences in the genetic regions encoding the dopamine receptors for each individual may help to elucidate part of the risk for opioid addiction and general substance abuse. Studies of the D2 Dopamine Receptor, in particular, have shown some promising results. One specific SNP is at the TaqI RFLP (rs1800497). In a study of 530 Han Chinese heroin-addicted individuals from a Methadone Maintenance Treatment Program, those with the specific genetic variation showed higher mean heroin consumption by around double those without the SNP.[62] This study helps to show the contribution of dopamine receptors to substance addiction and more specifically to opioid abuse.[62]

Neuroimaging has shown functional and structural alterations in the brain.[63] Chronic intake of opioids such as heroin may cause long-term effects in the orbitofrontal area (OFC), which is essential for regulating reward-related behaviors, emotional responses, and anxiety.[64] Moreover, neuroimaging and neuropsychological studies demonstrate dysregulation of circuits associated with emotion, stress and high impulsivity.[65]

Dependence

Opioid dependence can occur as

Drug dependence is an adaptive state associated with a withdrawal syndrome upon cessation of repeated exposure to a stimulus (e.g., drug intake).[47][48][49] Dependence is a component of a substance use disorder.[13][67] Opioid dependence can manifest as physical dependence, psychological dependence, or both.[66][48][67]

Increased

mechanistic target of rapamycin complex 2 (mTORC2).[47][68] As a result of downregulated signaling through these proteins, opiates cause VTA neuronal hyperexcitability and shrinkage (specifically, the size of the neuronal soma is reduced).[47] It has been shown that when an opiate-naive person begins using opiates in concentrations that induce euphoria, BDNF signaling increases in the VTA.[69]

Upregulation of the

cAMP response element binding protein (CREB), a gene transcription factor, in the nucleus accumbens is a common mechanism of psychological dependence among several classes of drugs of abuse.[66][47] Upregulation of the same pathway in the locus coeruleus is also a mechanism responsible for certain aspects of opioid-induced physical dependence.[66][47]

A scale was developed to compare the harm and dependence liability of 20 drugs.[70] The scale uses a rating of zero to three to rate physical dependence, psychological dependence, and pleasure to create a mean score for dependence.[70] Selected results can be seen in the chart below. Heroin and morphine both scored highest, at 3.0.[70]

Drug Mean Pleasure Psychological dependence Physical dependence
Heroin/Morphine 3.00 3.0 3.0 3.0
Cocaine 2.39 3.0 2.8 1.3
Alcohol 1.93 2.3 1.9 1.6
Benzodiazepines 1.83 1.7 2.1 1.8
Tobacco 2.21 2.3 2.6 1.8

Opioid receptors

A genetic basis for the efficacy of opioids in the treatment of pain has been demonstrated for several specific variations, but the evidence for clinical differences in opioid effects is ambiguous.

phenotypes, including opioid dependence, cocaine dependence, alcohol dependence, methamphetamine dependence/psychosis, response to naltrexone treatment, personality traits, and others. Major and minor variants have been reported for every receptor and ligand coding gene in both coding sequences, as well as regulatory regions.[71] Research on endogenous opioid receptors has focused around OPRM1 gene, which encodes the μ-opioid receptor, and the OPRK1 and OPRD1 genes, which encode the κ and δ receptors, respectively.[71] Newer approaches shift away from analysis of specific genes and regions, and are based on an unbiased screen of genes across the entire genome, which have no apparent relationship to the phenotype in question. These GWAS studies yield a number of implicated genes, although many of them code for seemingly unrelated proteins in processes such as cell adhesion, transcriptional regulation, cell structure determination, and RNA, DNA, and protein handling/modifying.[72]

118A>G variant

While over 100 variants have been identified for the opioid mu-receptor, the most studied mu-receptor variant is the non-synonymous 118A>G variant, which results in functional changes to the receptor, including lower binding site availability, reduced

exogenous opioids, requiring a higher dose to achieve the same therapeutic effect. This points to a potential for greater addictive capacity in individuals who require higher dosages to achieve pain control. But evidence linking the 118A>G variant to opioid dependence is mixed, with associations shown in a number of study groups, but negative results in other groups. One explanation for the mixed results is the possibility of other variants that are in linkage disequilibrium with the 118A>G variant and thus contribute to different haplotype patterns more specifically associated with opioid dependence.[73]

Non-opioid receptor genes

While opioid receptors have been the most widely studied, a number of other genes have been implicated in OUD. Higher numbers of

preproenkephalin gene, PENK, have been associated with opiate dependence.[74] There have been mixed results for the MCR2 gene, encoding melanocortin receptor type 2, implicating both protection and risk to heroin addiction.[74] A number of enzymes in the cytochrome P450 family may also play a role in dependence and overdose due to variance in breakdown of opioids and their receptors. There are also multiple potential complications with combining opioids with antidepressants and antiepileptic drugs (both common drugs for chronic pain patients) because of their effects on inducing CYP enzymes.[75] Genotyping of CYP2D6 in particular may play a role in helping patients with individualized treatment for OUD and other drug addictions.[75]

Prevention

The CDC gives specific recommendations for prescribers regarding initiation of opioids, clinically appropriate use of opioids, and assessing possible risks associated with opioid therapy.[76] Large U.S. retail pharmacy chains are implementing protocols, guidelines, and initiatives to take back unused opioids, providing naloxone kits, and being vigilant for suspicious prescriptions.[77][78][79] Insurance programs can help limit opioid use by setting quantity limits on prescriptions or requiring prior authorizations for certain medications.[80]

Opioid-related deaths

Naloxone is used for the emergency treatment of an overdose.[81] It can be given by many routes (e.g., intramuscular (IM), intravenous (IV), subcutaneous, intranasal, and inhalation) and acts quickly by displacing opioids from opioid receptors and preventing the activation of these receptors.[79] Naloxone kits are recommended for laypersons who may witness an opioid overdose, for people with large prescriptions for opioids, those in substance use treatment programs, and those recently released from incarceration.[82] Since this is a life-saving medication, many areas of the U.S. have implemented standing orders for law enforcement to carry and give naloxone as needed.[83][84] In addition, naloxone can be used to challenge a person's opioid abstinence status before starting a medication such as naltrexone, which is used in the management of opioid addiction.[85]

Good Samaritan laws typically protect bystanders who administer naloxone. In the U.S., at least 40 states have Good Samaritan laws to encourage bystanders to take action without fear of prosecution.[86] As of 2019, 48 states give pharmacists the authority to distribute naloxone without an individual prescription.[87]

Homicide, suicide, accidents and liver disease are also opioid-related causes of death for those with OUD.[88][89] Many of these causes of death are unnoticed due to the often limited information on death certificates.[88][90]

Mitigation

The "CDC Clinical Practice Guideline for Prescribing Opioids for Pain-United States, 2022" provides recommendations related to opioid misuse, OUD, and opioid overdoses.[16] It reports a lack of clinical evidence that "abuse-deterrent" opioids (e.g., OxyContin), as labeled by the U.S. Food and Drug Administration, are effective for OUD risk mitigation.[16][91] CDC guidance suggests the prescription of immediate-release opioids instead of opioids that have a long duration (long-acting) or opioids that are released over time (extended release).[16] Other recommendations include prescribing the lowest opioid dose that successfully addresses the pain in opioid-naïve patients and collaborating with patients who already take opioid therapy to maximize the effect of non-opioid analgesics.[16]

While receiving opioid therapy, patients should be periodically evaluated for opioid-related complications and clinicians should review state prescription drug monitoring program systems.[16] The latter should be assessed to reduce the risk of overdoses in patients due to their opioid dose or medication combinations.[16] For patients receiving opioid therapy in whom the risks outweigh the benefits, clinicians and patients should develop a treatment plan to decrease their opioid dose incrementally.[16]

For more specific mitigation strategies regarding opioid overdoses, see opioid overdose § Prevention.

Management

Opioid use disorders typically require long-term treatment and care with the goal of reducing the person's risks and improving their long-term physical and psychological condition.[44]

First-line management involves the use of opioid replacement therapies, particularly methadone and buprenorphine/naloxone. Withdrawal management alone is strongly discouraged, because of its association with elevated risks of HIV and hepatitis C transmission, high rates of overdose deaths, and nearly universal relapse.[92][93] This approach is seen as ineffective without plans for transition to long-term evidence-based addiction treatment, such as opioid agonist treatment.[53] Though treatment reduces mortality rates, the first four weeks after treatment begins and the four weeks after treatment ceases are the riskiest times for drug-related deaths.[7] These periods of increased vulnerability are significant because many of those in treatment leave programs during these periods.[7] There is evidence that people with opioid use disorder who are dependent on pharmaceutical opioids may require a different management approach from those who take heroin.[94]

Medication