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With chronic use for treatment of [[pain]], dependence may lead to substance abuse and "aberrant medication-taking behaviors" may occur.<ref name="pmid17227935">{{cite journal |author=Martell BA, O'Connor PG, Kerns RD, ''et al'' |title=Systematic review: opioid treatment for chronic back pain: prevalence, efficacy, and association with addiction |journal=Ann. Intern. Med. |volume=146 |issue=2 |pages=116–27 |year=2007 |pmid=17227935 |doi= |url=http://www.annals.org/cgi/content/full/146/2/116 |issn=}}</ref> From 2000-2005, the abuse of prescribed opiods, especially [[oxycodone|oxycodone extended release (OxyContin)]] and [[hydrocodone]], has increased.<ref name="pmid16202959">{{cite journal| author=Cicero TJ, Inciardi JA, Muñoz A| title=Trends in abuse of Oxycontin and other opioid analgesics in the United States: 2002-2004. | journal=J Pain | year= 2005 | volume= 6 | issue= 10 | pages= 662-72 | pmid=16202959 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16202959 | doi=10.1016/j.jpain.2005.05.004 }} </ref> From Contracts may reduce abuse, but comparative studies provide conflicting results.<ref>{{Cite journal | doi = 10.1059/0003-4819-152-11-201006010-00004 | volume = 152 | issue = 11  pages = 712-720 | last = Starrels | first = Joanna L. | coauthors = William C. Becker, Daniel P. Alford, Alok Kapoor, Arthur Robinson Williams, Barbara J. Turner | title = Systematic Review: Treatment Agreements and Urine Drug Testing to Reduce Opioid Misuse in Patients With Chronic Pain | journal = Annals of Internal Medicine | accessdate = 2010-06-01 | date = 2010-06-01 | url = http://www.annals.org/content/152/11/712.abstract }}</ref> Most agreements stated, "patients agreed not to abuse illicit drugs or alcohol, obtain opioids from more than 1 provider or pharmacy, or request a refill before the previous prescription should have been  completed."
With chronic use for treatment of [[pain]], dependence may lead to substance abuse and "aberrant medication-taking behaviors" may occur.<ref name="pmid17227935">{{cite journal |author=Martell BA, O'Connor PG, Kerns RD, ''et al'' |title=Systematic review: opioid treatment for chronic back pain: prevalence, efficacy, and association with addiction |journal=Ann. Intern. Med. |volume=146 |issue=2 |pages=116–27 |year=2007 |pmid=17227935 |doi= |url=http://www.annals.org/cgi/content/full/146/2/116 |issn=}}</ref> From 2000-2005, the abuse of prescribed opiods, especially [[oxycodone|oxycodone extended release (OxyContin)]] and [[hydrocodone]], has increased.<ref name="pmid16202959">{{cite journal| author=Cicero TJ, Inciardi JA, Muñoz A| title=Trends in abuse of Oxycontin and other opioid analgesics in the United States: 2002-2004. | journal=J Pain | year= 2005 | volume= 6 | issue= 10 | pages= 662-72 | pmid=16202959 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16202959 | doi=10.1016/j.jpain.2005.05.004 }} </ref> From Contracts may reduce abuse, but comparative studies provide conflicting results.<ref>{{Cite journal | doi = 10.1059/0003-4819-152-11-201006010-00004 | volume = 152 | issue = 11  pages = 712-720 | last = Starrels | first = Joanna L. | coauthors = William C. Becker, Daniel P. Alford, Alok Kapoor, Arthur Robinson Williams, Barbara J. Turner | title = Systematic Review: Treatment Agreements and Urine Drug Testing to Reduce Opioid Misuse in Patients With Chronic Pain | journal = Annals of Internal Medicine | accessdate = 2010-06-01 | date = 2010-06-01 | url = http://www.annals.org/content/152/11/712.abstract }}</ref> Most agreements stated, "patients agreed not to abuse illicit drugs or alcohol, obtain opioids from more than 1 provider or pharmacy, or request a refill before the previous prescription should have been  completed."


==Tolerance==
==Terminology==
===Tolerance===


''[[Drug tolerance|Tolerance]]'' is the process whereby neuroadaptation occurs (through receptor desensitization) resulting in reduced drug effects. Tolerance is more pronounced for some effects than for others - tolerance occurs quickly to the effects on mood, itching, urinary retention, and respiratory depression, but occurs more slowly to the analgesia and other physical side effects.
''[[Drug tolerance|Tolerance]]'' is the process whereby neuroadaptation occurs (through receptor desensitization) resulting in reduced drug effects. Tolerance is more pronounced for some effects than for others - tolerance occurs quickly to the effects on mood, itching, urinary retention, and respiratory depression, but occurs more slowly to the analgesia and other physical side effects.
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Magnesium and zinc deficiency speed up the development of tolerance to opioids and relative deficiency of these minerals is quite common<ref>http://www.worldwidehealthcenter.net/articles-360.html</ref> due to low magnesium/zinc content in food and use of substances which deplete them including diuretics (such as alcohol, caffeine/theophylline) and smoking. Reducing intake of these substances and taking zinc/magnesium supplements may slow the development of tolerance to opiates.
Magnesium and zinc deficiency speed up the development of tolerance to opioids and relative deficiency of these minerals is quite common<ref>http://www.worldwidehealthcenter.net/articles-360.html</ref> due to low magnesium/zinc content in food and use of substances which deplete them including diuretics (such as alcohol, caffeine/theophylline) and smoking. Reducing intake of these substances and taking zinc/magnesium supplements may slow the development of tolerance to opiates.


==Dependence==
===Dependence===
'[[Drug dependence|Dependence]]'' is characterised by extremely unpleasant withdrawal symptoms that occur if opioid use is abruptly discontinued after tolerance has developed.  The withdrawal symptoms include severe [[dysphoria]], [[sweating]], [[nausea]], rhinorrea, depression, severe fatigue, [[vomiting]] and [[pain]].  Slowly reducing the intake of opioids over days and weeks will reduce or eliminate the withdrawal symptoms.<ref>''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).</ref>  The speed and severity of withdrawal depends on the half-life of the opioid — [[heroin]] and [[morphine]] withdrawal occur more quickly and are more severe than [[methadone]] withdrawal, but methadone withdrawal takes longer.  The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. The symptoms of opioid withdrawal can also be treated with other medications, but with a low efficacy.<ref>Hermann D, Klages E, Welzel H, Mann K, Croissant B. Low efficacy of non-opioid drugs in opioid withdrawal symptoms.  Addict Biol. 2005 Jun;10(2):165-9. PMID: 16191669 </ref>  Dependence also occurs for most other drugs, including [[caffeine]] and [[alcohol]].  The DSM-IV Criteria for opioid withdrawal is (available from: http://www.ncbi.nlm.nih.gov/books/NBK64247/)
'[[Drug dependence|Dependence]]'' is characterised by extremely unpleasant withdrawal symptoms that occur if opioid use is abruptly discontinued after tolerance has developed.  The withdrawal symptoms include severe [[dysphoria]], [[sweating]], [[nausea]], rhinorrea, depression, severe fatigue, [[vomiting]] and [[pain]].  Slowly reducing the intake of opioids over days and weeks will reduce or eliminate the withdrawal symptoms.<ref>''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).</ref>  The speed and severity of withdrawal depends on the half-life of the opioid — [[heroin]] and [[morphine]] withdrawal occur more quickly and are more severe than [[methadone]] withdrawal, but methadone withdrawal takes longer.  The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. The symptoms of opioid withdrawal can also be treated with other medications, but with a low efficacy.<ref>Hermann D, Klages E, Welzel H, Mann K, Croissant B. Low efficacy of non-opioid drugs in opioid withdrawal symptoms.  Addict Biol. 2005 Jun;10(2):165-9. PMID: 16191669 </ref>  Dependence also occurs for most other drugs, including [[caffeine]] and [[alcohol]].  The DSM-IV Criteria for opioid withdrawal is (available from: http://www.ncbi.nlm.nih.gov/books/NBK64247/)


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D. The symptoms are not due to a general medical condition and are not better accounted for by another mental disorder.
D. The symptoms are not due to a general medical condition and are not better accounted for by another mental disorder.


==Addiction==
===Addiction===
''[[Drug addiction|Addiction]]'' is the process whereby physical and/or psychological addiction develops to a drug - including opioids.  The withdrawal symptoms can reinforce the addiction, driving the user to continue taking the drug.  Psychological addiction is more common in people taking opioids recreationally, it is rare in patients taking opioids for pain relief.<ref>''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).</ref>  
''[[Drug addiction|Addiction]]'' is the process whereby physical and/or psychological addiction develops to a drug - including opioids.  The withdrawal symptoms can reinforce the addiction, driving the user to continue taking the drug.  Psychological addiction is more common in people taking opioids recreationally, it is rare in patients taking opioids for pain relief.<ref>''Oxford Textbook of Palliative Medicine'', 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).</ref>  


==Abuse==
===Abuse===
''[[Drug abuse]]'' is the misuse of drugs producing negative consequences.
''[[Drug abuse]]'' is the misuse of drugs producing negative consequences.
==Differential Diagnosis==
==Differential Diagnosis==
*Opioid-induced mental disorders
*Opioid-induced mental disorders
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==Epidemiology and Demographics==
==Epidemiology and Demographics==
===Prevalence===
===Prevalence===
The 12 month prevalence of opioid use disorder is 370 per 100,000 (0.37%) in ages 18 years and older in the community population.<ref name=DSMV>{{cite book | title = Diagnostic and statistical manual of mental disorders : DSM-5 | publisher = American Psychiatric Association | location = Washington, D.C | year = 2013 | isbn = 0890425558 }}</ref>  
The 12 month prevalence of opioid use disorder is 370 per 100,000 (0.37%) in ages 18 years and older in the community population.<ref name=DSMV>{{cite book | title = Diagnostic and statistical manual of mental disorders : DSM-5 | publisher = American Psychiatric Association | location = Washington, D.C | year = 2013 | isbn = 0890425558 }}</ref>
==Risk Factors==
 
*Family
*Genetic predisposition
*Individual
*Peer
*Social environmental factors<ref name=DSMV>{{cite book | title = Diagnostic and statistical manual of mental disorders : DSM-5 | publisher = American Psychiatric Association | location = Washington, D.C | year = 2013 | isbn = 0890425558 }}</ref>
==Diagnostic Criteria==
==Diagnostic Criteria==
===DSM-V Diagnostic Criteria for Opioid Use Disorder<ref name=DSMV>{{cite book | title = Diagnostic and statistical manual of mental disorders : DSM-5 | publisher = American Psychiatric Association | location = Washington, D.C | year = 2013 | isbn = 0890425558 }}</ref>===
===DSM-V Diagnostic Criteria for Opioid Use Disorder<ref name=DSMV>{{cite book | title = Diagnostic and statistical manual of mental disorders : DSM-5 | publisher = American Psychiatric Association | location = Washington, D.C | year = 2013 | isbn = 0890425558 }}</ref>===
{{cquote|
{{cquote|
*A.A problematic pattern of opioid use leading to clinically significant impairment or distress,as manifested by at least two of the following, occurring within a 12-month period:
*A. A problematic pattern of opioid use leading to clinically significant impairment or distress,as manifested by at least two of the following, occurring within a 12-month period:
:*1.Opioids are often taken in larger amounts or over a longer period than was intended.
:*1. Opioids are often taken in larger amounts or over a longer period than was intended.
:*2.There is a persistent desire or unsuccessful efforts to cut down or control opioid use.
:*2. There is a persistent desire or unsuccessful efforts to cut down or control opioid use.
:*3.A great deal of time is spent in activities necessary to obtain the opioid, use the opioid, or recover from its effects.
:*3. A great deal of time is spent in activities necessary to obtain the opioid, use the opioid, or recover from its effects.
:*4.Craving, or a strong desire or urge to use opioids.
:*4. Craving, or a strong desire or urge to use opioids.
:*5.Recurrent opioid use resulting in a failure to fulfill major role obligations at work,school, or home.
:*5. Recurrent opioid use resulting in a failure to fulfill major role obligations at work, school, or home.
:*6.Continued opioid use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of opioids.
:*6. Continued opioid use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of opioids.
:*7.Important social, occupational, or recreational activities are given up or reduced because of opioid use.
:*7. Important social, occupational, or recreational activities are given up or reduced because of opioid use.
:*8.Recurrent opioid use in situations in which it is physically hazardous.
:*8. Recurrent opioid use in situations in which it is physically hazardous.
:*9.Continued opioid use despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance.
:*9. Continued opioid use despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance.
:*10.Tolerance, as defined by either of the following:
:*10. Tolerance, as defined by either of the following:
::*a.A need for markedly increased amounts of opioids to achieve intoxication or desired effect.
::*a. A need for markedly increased amounts of opioids to achieve intoxication or desired effect.
::*b.A markedly diminished effect with continued use of the same amount of an opioid.
::*b. A markedly diminished effect with continued use of the same amount of an opioid.
<SMALL>''Note:This criterion is not considered to be met for those taking opioids solely under appropriate medical supervision.''</SMALL>
<SMALL>''Note:This criterion is not considered to be met for those taking opioids solely under appropriate medical supervision.''</SMALL>
:*11.Withdrawal, as manifested by either of the following:
:*11. Withdrawal, as manifested by either of the following:
::*a.The characteristic opioid withdrawal syndrome.  
::*a. The characteristic opioid withdrawal syndrome.  
::*b.Opioids (or a closely related substance) are taken to relieve or avoid withdrawal symptoms.
::*b. Opioids (or a closely related substance) are taken to relieve or avoid withdrawal symptoms.


<SMALL>''Note:This criterion is not considered to be met for those individuals taking opioids solely under appropriate medical supervision .''</SMALL>
<SMALL>''Note:This criterion is not considered to be met for those individuals taking opioids solely under appropriate medical supervision .''</SMALL>


Specify if:
Specify if:
*In early remission: After full criteria for opioid use disorder were previously met, none of the criteria for opioid use disorder have been met for at least 3 months but for less than 12 months (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).
* In early remission: After full criteria for opioid use disorder were previously met, none of the criteria for opioid use disorder have been met for at least 3 months but for less than 12 months (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).


*In sustained remission: After full criteria for opioid use disorder were previously met,none of the criteria for opioid use disorder have been met at any time during a period
* In sustained remission: After full criteria for opioid use disorder were previously met,none of the criteria for opioid use disorder have been met at any time during a period of 12 months or longer (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).
of 12 months or longer (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).


Specify if:
Specify if:
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*In a controlled environment: This additional specifier is used if the individual is in an environment where access to opioids is restricted.
*In a controlled environment: This additional specifier is used if the individual is in an environment where access to opioids is restricted.
}}
}}
==Opioid Dependence Treatment==


==References==
==References==

Revision as of 22:42, 13 November 2014

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Kiran Singh, M.D. [2]

Synonyms and keywords: Opioid use disorder

Overview

With chronic use for treatment of pain, dependence may lead to substance abuse and "aberrant medication-taking behaviors" may occur.[1] From 2000-2005, the abuse of prescribed opiods, especially oxycodone extended release (OxyContin) and hydrocodone, has increased.[2] From Contracts may reduce abuse, but comparative studies provide conflicting results.[3] Most agreements stated, "patients agreed not to abuse illicit drugs or alcohol, obtain opioids from more than 1 provider or pharmacy, or request a refill before the previous prescription should have been completed."

Terminology

Tolerance

Tolerance is the process whereby neuroadaptation occurs (through receptor desensitization) resulting in reduced drug effects. Tolerance is more pronounced for some effects than for others - tolerance occurs quickly to the effects on mood, itching, urinary retention, and respiratory depression, but occurs more slowly to the analgesia and other physical side effects.

Tolerance to opioids is attenuated by a number of substances, including calcium channel blockers[4][5], intrathecal magnesium[6] and zinc[7], and NMDA antagonists such as ketamine.[8]

Magnesium and zinc deficiency speed up the development of tolerance to opioids and relative deficiency of these minerals is quite common[9] due to low magnesium/zinc content in food and use of substances which deplete them including diuretics (such as alcohol, caffeine/theophylline) and smoking. Reducing intake of these substances and taking zinc/magnesium supplements may slow the development of tolerance to opiates.

Dependence

'Dependence is characterised by extremely unpleasant withdrawal symptoms that occur if opioid use is abruptly discontinued after tolerance has developed. The withdrawal symptoms include severe dysphoria, sweating, nausea, rhinorrea, depression, severe fatigue, vomiting and pain. Slowly reducing the intake of opioids over days and weeks will reduce or eliminate the withdrawal symptoms.[10] The speed and severity of withdrawal depends on the half-life of the opioid — heroin and morphine withdrawal occur more quickly and are more severe than methadone withdrawal, but methadone withdrawal takes longer. The acute withdrawal phase is often followed by a protracted phase of depression and insomnia that can last for months. The symptoms of opioid withdrawal can also be treated with other medications, but with a low efficacy.[11] Dependence also occurs for most other drugs, including caffeine and alcohol. The DSM-IV Criteria for opioid withdrawal is (available from: http://www.ncbi.nlm.nih.gov/books/NBK64247/)

A. Either of the following:

  • Cessation of or reduction in opioid use that has been heavy and for several weeks or longer
  • Administration of an opioid antagonist after a period of opioid use

B. Three (or more) of the following (developing within minutes to several days after Criterion A):

  • Diarrhea
  • Dysphoric mood
  • Fever
  • Insomnia
  • Lacrimation or rhinorrhea
  • Muscle aches
  • Nausea or vomiting
  • Pupillary dilation, piloerection, or sweating
  • Yawning

C. The symptoms in Criterion B cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

D. The symptoms are not due to a general medical condition and are not better accounted for by another mental disorder.

Addiction

Addiction is the process whereby physical and/or psychological addiction develops to a drug - including opioids. The withdrawal symptoms can reinforce the addiction, driving the user to continue taking the drug. Psychological addiction is more common in people taking opioids recreationally, it is rare in patients taking opioids for pain relief.[12]

Abuse

Drug abuse is the misuse of drugs producing negative consequences.

Differential Diagnosis

  • Opioid-induced mental disorders
  • Other substance intoxication
  • Other withdrawal disorders

Epidemiology and Demographics

Prevalence

The 12 month prevalence of opioid use disorder is 370 per 100,000 (0.37%) in ages 18 years and older in the community population.[13]

Diagnostic Criteria

DSM-V Diagnostic Criteria for Opioid Use Disorder[13]

  • A. A problematic pattern of opioid use leading to clinically significant impairment or distress,as manifested by at least two of the following, occurring within a 12-month period:
  • 1. Opioids are often taken in larger amounts or over a longer period than was intended.
  • 2. There is a persistent desire or unsuccessful efforts to cut down or control opioid use.
  • 3. A great deal of time is spent in activities necessary to obtain the opioid, use the opioid, or recover from its effects.
  • 4. Craving, or a strong desire or urge to use opioids.
  • 5. Recurrent opioid use resulting in a failure to fulfill major role obligations at work, school, or home.
  • 6. Continued opioid use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of opioids.
  • 7. Important social, occupational, or recreational activities are given up or reduced because of opioid use.
  • 8. Recurrent opioid use in situations in which it is physically hazardous.
  • 9. Continued opioid use despite knowledge of having a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance.
  • 10. Tolerance, as defined by either of the following:
  • a. A need for markedly increased amounts of opioids to achieve intoxication or desired effect.
  • b. A markedly diminished effect with continued use of the same amount of an opioid.

Note:This criterion is not considered to be met for those taking opioids solely under appropriate medical supervision.

  • 11. Withdrawal, as manifested by either of the following:
  • a. The characteristic opioid withdrawal syndrome.
  • b. Opioids (or a closely related substance) are taken to relieve or avoid withdrawal symptoms.

Note:This criterion is not considered to be met for those individuals taking opioids solely under appropriate medical supervision .

Specify if:

  • In early remission: After full criteria for opioid use disorder were previously met, none of the criteria for opioid use disorder have been met for at least 3 months but for less than 12 months (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).
  • In sustained remission: After full criteria for opioid use disorder were previously met,none of the criteria for opioid use disorder have been met at any time during a period of 12 months or longer (with the exception that Criterion A4, “Craving, or a strong desire or urge to use opioids,” may be met).

Specify if:

  • On maintenance therapy: This additional specifier is used if the individual is taking a prescribed agonist medication such as methadone or buprenorphine and none of the criteria for opioid use disorder have been met for that class of medication (except tolerance to, or withdrawal from, the agonist). This category also applies to those Individuals being maintained on a partial agonist, an agonist/antagonist, or a full antagonist such as oral naltrexone or depot naltrexone.
  • In a controlled environment: This additional specifier is used if the individual is in an environment where access to opioids is restricted.

References

  1. Martell BA, O'Connor PG, Kerns RD; et al. (2007). "Systematic review: opioid treatment for chronic back pain: prevalence, efficacy, and association with addiction". Ann. Intern. Med. 146 (2): 116–27. PMID 17227935.
  2. Cicero TJ, Inciardi JA, Muñoz A (2005). "Trends in abuse of Oxycontin and other opioid analgesics in the United States: 2002-2004". J Pain. 6 (10): 662–72. doi:10.1016/j.jpain.2005.05.004. PMID 16202959.
  3. Starrels, Joanna L. (2010-06-01). "Systematic Review: Treatment Agreements and Urine Drug Testing to Reduce Opioid Misuse in Patients With Chronic Pain". Annals of Internal Medicine. 152 (11 pages = 712-720). doi:10.1059/0003-4819-152-11-201006010-00004. Retrieved 2010-06-01. Unknown parameter |coauthors= ignored (help)
  4. Santillán R, Maestre JM, Hurlé MA, Flórez J. "Enhancement of opiate analgesia by nimodipine in cancer patients chronically treated with morphine: a preliminary report." Pain. 1994 Jul;58(1):129-32. PMID 7970835
  5. Smith FL, Dombrowski DS, Dewey WL. "Involvement of intracellular calcium in morphine tolerance in mice." Pharmacology, Biochemistry, and Behavior. 1999 Feb;62(2):381-8. PMID 9972707
  6. McCarthy RJ, Kroin JS, Tuman KJ, Penn RD, Ivankovich AD. "Antinociceptive potentiation and attenuation of tolerance by intrathecal co-infusion of magnesium sulfate and morphine in rats." Anesthesia and Analgesia. 1998 Apr;86(4):830-6. PMID 9539610
  7. Larson AA, Kovács KJ, Spartz AK. "Intrathecal Zn2+ attenuates morphine antinociception and the development of acute tolerance." European Journal of Pharmacology. 2000 Nov 3;407(3):267-72. PMID 11068022
  8. Wong CS, Cherng CH, Luk HN, Ho ST, Tung CS. "Effects of NMDA receptor antagonists on inhibition of morphine tolerance in rats: binding at mu-opioid receptors." Eur J Pharmacol. 1996 Feb 15;297(1-2):27-33. PMID 8851162
  9. http://www.worldwidehealthcenter.net/articles-360.html
  10. Oxford Textbook of Palliative Medicine, 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).
  11. Hermann D, Klages E, Welzel H, Mann K, Croissant B. Low efficacy of non-opioid drugs in opioid withdrawal symptoms. Addict Biol. 2005 Jun;10(2):165-9. PMID: 16191669
  12. Oxford Textbook of Palliative Medicine, 3rd ed. (Doyle D, Hanks G, Cherney I and Calman K, eds. Oxford University Press, 2004).
  13. 13.0 13.1 13.2 Diagnostic and statistical manual of mental disorders : DSM-5. Washington, D.C: American Psychiatric Association. 2013. ISBN 0890425558.

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