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Opioid Toxicity and Withdrawal


Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;

Rika O’Malley

, MD, Grand Strand Medical Center

Reviewed/Revised Dec 2022

Opioids are euphoriants that cause sedation. Respiratory depression may occur with high doses and can be managed with antidotes (eg, naloxone) or endotracheal intubation and mechanical ventilation. Withdrawal manifests initially as anxiety and drug craving, followed by increased respiratory rate, diaphoresis, yawning, lacrimation, rhinorrhea, mydriasis, and stomach cramps and later by piloerection, tremors, muscle twitches, tachycardia, hypertension, fever, chills, anorexia, nausea, vomiting, and diarrhea. Diagnosis is clinical plus with urine tests. Withdrawal can be treated by substitution with a long-acting opioid (eg, methadone) or buprenorphine (a mixed opioid agonist-antagonist).

“Opioid” is a term for a number of natural substances (originally derived from the opium poppy) and their semisynthetic and synthetic analogues that bind to specific opioid receptors. Opioids, which are potent analgesics with a limited role in management of cough and diarrhea, are also common drugs of abuse because of their wide availability and euphoriant properties; see also Opioid Analgesics Opioid Analgesics Nonopioid and opioid analgesics are the main drugs used to treat pain. Antidepressants, antiseizure drugs, and other central nervous system (CNS)–active drugs may also be used for chronic or... read more and Opioid Use Disorder and Rehabilitation Opioid Use Disorder and Rehabilitation “Opioid” is a term for a number of natural substances (originally derived from the opium poppy) and their semisynthetic and synthetic analogs that bind to specific opioid receptors. Opioids... read more .

Pathophysiology of Opioid Toxicity or Withdrawal

There are 3 main opioid receptors: delta, kappa, and mu. They occur throughout the central nervous system but particularly in areas and tracts associated with pain perception. Receptors are also located in some sensory nerves, on mast cells, and in some cells of the gastrointestinal tract.

Opioid receptors are stimulated by endogenous endorphins, which generally produce analgesia and a sense of well-being. Opioids are used therapeutically, primarily as analgesics. Opioids vary in their receptor activity, and some (eg, buprenorphine) have combined agonist and antagonist actions. Compounds with pure antagonist activity (eg, naloxone, naltrexone) are available.

Exogenous opioids can be taken by almost any route: orally, intravenously, subcutaneously, rectally, through the nasal membranes, or inhaled as smoke. Peak effects are reached about 10 minutes after IV injection, 10 to 15 minutes after nasal insufflation, and 90 to 120 minutes after oral ingestion, although time to peak effects and duration of effect vary considerably depending on the specific drug.

Chronic effects

Opioid tolerance develops quickly, with escalating dose requirements. Tolerance to the various effects of opioids frequently develops unevenly. Heroin users, for example, may become relatively tolerant to the drug’s euphoric and respiratory depression effects but continue to have constricted pupils and constipation.

Long-term effects of the opioids themselves are minimal; even decades of methadone use appear to be well tolerated physiologically, although some long-term opioid users experience chronic constipation, excessive sweating, peripheral edema, drowsiness, and decreased libido. However, many long-term users who inject opioids have adverse effects from contaminants (eg, talc) and adulterants (eg, nonprescription stimulant drugs) and cardiac, pulmonary, and hepatic damage due to infections such as HIV infection Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more Human Immunodeficiency Virus (HIV) Infection and hepatitis Overview of Acute Viral Hepatitis Acute viral hepatitis is diffuse liver inflammation caused by specific hepatotropic viruses that have diverse modes of transmission and epidemiologies. A nonspecific viral prodrome is followed... read more B or C, which are spread by needle sharing and nonsterile injection techniques (see Injection Drug Use Injection Drug Use A number of drugs of abuse are administered by injection to achieve a more rapid or potent effect or both. Drugs are typically injected IV but may be injected subcutaneously, IM, or even sublingually... read more ).


Symptoms and Signs of Opioid Toxicity or Withdrawal

Acute effects

Acute opioid intoxication is characterized by euphoria and drowsiness. Mast cell effects (eg, flushing, itching) are common, particularly with morphine. Gastrointestinal effects include nausea, vomiting, decreased bowel sounds, and constipation.

Toxicity or overdose

The main toxic effect is decreased respiratory rate and depth, which can progress to apnea. Other complications (eg, pulmonary edema, which usually develops within minutes to a few hours after opioid overdose) and death result primarily from hypoxia. Pupils are miotic. Delirium, hypotension, bradycardia, decreased body temperature, and urinary retention may also occur.

Normeperidine, a metabolite of meperidine, accumulates with repeated use (including therapeutic); it stimulates the central nervous system and may cause seizure activity.

Serotonin syndrome Serotonin Syndrome Serotonin syndrome is a potentially life-threatening condition resulting from increased central nervous system serotonergic activity that is usually drug related. Symptoms may include mental... read more occasionally occurs when fentanyl, meperidine, tramadol, methadone, codeine, or oxycodone is taken concomitantly with other drugs that have serotonergic effects (eg, selective serotonin reuptake inhibitors, monoamine oxidase inhibitors). Serotonin syndrome consists of one or more of the following:

  • Hypertonia

  • Tremor and hyperreflexia

  • Spontaneous, inducible, or ocular clonus

  • Diaphoresis and autonomic instability

  • Agitation

  • Temperature > 38° plus ocular or inducible clonus

Although rare among inhalational heroin users, spongiform leukoencephalopathy has been reported. The symptoms depend on the timing of presentation and may show motor restlessness, apathy, ataxia, or paralysis. The symptoms may resolve, or can progress to autonomic dysregulation and death.


The opioid withdrawal syndrome usually includes symptoms and signs of central nervous system hyperactivity. Onset and duration of the syndrome depend on the specific drug and its half-life. Symptoms may appear as early as 4 hours after the last dose of heroin, peak within 48 to 72 hours, and subside after about a week. Anxiety and a craving for the drug are followed by increased resting respiratory rate (> 16 breaths/minute), usually with diaphoresis, yawning, lacrimation, rhinorrhea, mydriasis, and stomach cramps. Later, piloerection (gooseflesh), tremors, muscle twitching, tachycardia, hypertension, fever and chills, anorexia, nausea, vomiting, and diarrhea may develop.

Opioid withdrawal does not cause fever, seizures, or altered mental status. Although it may be distressingly symptomatic, opioid withdrawal is not fatal.

The withdrawal syndrome in people who were taking methadone (which has a long half-life) develops more slowly and may be less acutely severe than heroin withdrawal, although users may describe it as worse. Even after the withdrawal syndrome remits, lethargy, malaise, anxiety, and disturbed sleep may persist up to several months. Drug craving may persist for years.

Diagnosis of Opioid Toxicity or Withdrawal

  • Usually a clinical diagnosis

Diagnosis of opioid use is usually made clinically and sometimes with urine drug testing Drug Testing Drug testing is done primarily to screen people systematically or randomly for evidence of use of one or more substances with potential for abuse. Testing may be done in the following: Certain... read more ; laboratory tests are done as needed to identify drug-related complications. Drug levels are not usually measured.

Treatment of Opioid Toxicity or Withdrawal

  • Supportive therapy

  • For opioid withdrawal, sometimes drug therapy (eg, with an opioid agonist, opioid agonist-antagonist, opioid antagonist, or clonidine)

Toxicity or overdose

Treatment to maintain the airway and support breathing is the first priority.

  • Naloxone 0.4 mg to 2 mg IV

  • Sometimes endotracheal intubation

Patients with spontaneous respirations can be treated with an opioid antagonist, typically naloxone 0.4 mg to 2 mg IV (for children < 20 kg, 0.1 mg/kg); naloxone has no agonist activity and a very short half-life (see table Symptoms and Treatment of Specific Poisons Symptoms and Treatment of Specific Poisons Symptoms and Treatment of Specific Poisons ). Naloxone rapidly reverses unconsciousness and apnea due to an opioid in most patients. If IV access is not immediately available, IM, subcutaneously, or intranasal administration is also effective. A 2nd or 3rd dose can be given if there is no response within 2 minutes. Massive opioid overdose and intoxication with synthetic opioids such as the fentanyl derivatives may require higher doses of naloxone.

Because some patients become agitated, delirious, and combative as consciousness returns and because naloxone precipitates acute withdrawal, soft physical restraints may be indicated if these symptoms occur and should be applied before naloxone is given. To ameliorate withdrawal in long-term users, some experts suggest titrating very small doses of naloxone (0.1 mg) when the clinical situation does not require emergency total reversal.

Apneic patients can initially be treated with naloxone 2 mg IV if it can be given without delay; note that the dose is higher than for patients who are only somnolent. In some parts of the US and some countries, naloxone is available without a prescription so apneic patients can be rescued by friends or family. When naloxone is available and given quickly, endotracheal intubation is rarely required.

Patients should be observed for several hours after they regain spontaneous respirations. Because the duration of action of naloxone is less than that of some opioids, respiratory depression can recur within several hours of an overdose of methadone or sustained-released oxycodone or morphine tablets. Thus, the duration of observation should vary depending on the half-life of the opioid involved. Typically, patients who took longer-acting opioids should be admitted for observation; patients who took short-acting opioids may be discharged after several hours.

If respiratory depression recurs, naloxone should be readministered at an appropriate dose. The best dosing regimen is unclear. Many clinicians use repeat bolus doses of the same dose that was effective initially. Others use continuous naloxone infusion; they typically begin with about two thirds of the initially effective dose per hour. In theory, the continuous infusion should allow the dose to be titrated to maintain respiratory rate without triggering withdrawal; however, in practice this can be difficult to do and the patient's life is dependent on the security of the IV line—respiratory depression will quickly recur if the infusion is interrupted (eg, by the patient pulling out the IV). Both regimens require close monitoring, typically in an intensive care unit.

Patients should be observed until no naloxone pharmacologic activity is present and they have no opioid-related symptoms. The serum half-life of naloxone is about 1 hour, so an observation period of 2 to 3 hours after use of naloxone should clarify disposition. The half-life of IV heroin is relatively short, and recurrent respiratory depression after naloxone reversal of IV heroin is rare.

Withdrawal and detoxification

Treatment may involve several strategies:

  • No treatment (“cold turkey”)

  • Substitution with buprenorphine or methadone

  • Clonidine to relieve symptoms

  • Long-term support and possibly naltrexone

The opioid withdrawal syndrome is self-limited and, although severely uncomfortable, is not life threatening. Minor metabolic and physical withdrawal effects may persist up to 6 months. Withdrawal is typically managed in outpatient settings, unless patients require hospitalization for concurrent medical or mental health problems.

Options for management of withdrawal include allowing the process to run its course (“cold turkey”) after the patient’s last opioid dose and giving another opioid (substitution) that can be tapered on a controlled schedule.

Medication-assisted treatment with buprenorphine and naloxone has become the primary choice of treatment.

Buprenorphine, a partial opioid agonist—usually given sublingually—has been successfully used in treatment of withdrawal. Naloxone is added to buprenorphine to reduce abuse potential. When taken sublingually, the buprenorphine (opioid agonist) effects predominate, reducing withdrawal symptoms. If crushed and injected, the naloxone effects predominate, increasing withdrawal symptoms. The first dose of buprenorphine is given sublingually when the first signs of withdrawal appear. The dose needed to effectively control severe symptoms is titrated as quickly as possible; sublingual doses of 8 to 16 mg/day are typically used. Buprenorphine is then tapered over several weeks.

The Substance Abuse and Mental Health Services Administration (SAMHSA) provides information on buprenorphine and the training required to qualify for a waiver to prescribe the drug, as well as protocols for using buprenorphine for detoxification or maintenance therapy (which are available for download).

Methadone is provided only by SAMHSA-certified opioid treatment programs and in acute care settings under limited circumstances. Methadone is given orally in the smallest amount that prevents severe, but not necessarily all symptoms of withdrawal. The typical initial dose range is 10 to 30 mg. The titration should be individualized. The dose should not be increased by any more than 10 mg every 5 days. Once initial withdrawal is stabilized, the common daily dose is 60 to 120 mg per day.

Symptom scales are available for estimating the appropriate dose. Higher doses should be given when evidence of withdrawal is observed. After the appropriate dose has been established, it should be reduced progressively by 10 to 20% each day unless the decision is made to continue the drug at a stable dose (methadone maintenance Maintenance “Opioid” is a term for a number of natural substances (originally derived from the opium poppy) and their semisynthetic and synthetic analogs that bind to specific opioid receptors. Opioids... read more ). During tapering of the drug, patients commonly become anxious and request more of the drug.

Methadone withdrawal for people with opioid use disorder who have been in a methadone maintenance program may be particularly difficult because their dose of methadone may be as high as 100 mg once/day; in these patients, the dose should be gradually reduced to 60 mg once/day over several weeks before attempting complete detoxification.

Methadone has been reported to be associated with QTc prolongation and serious arrhythmias including torsades de pointes (see also Long QT Syndrome and Torsades de Pointes Torsades de Pointes Ventricular Tachycardia Torsades de pointes ventricular tachycardia is a specific form of polymorphic ventricular tachycardia in patients with a long QT interval. It is characterized by rapid, irregular QRS complexes... read more ). Thus, it should be used very carefully with appropriate patient evaluation and monitoring during initiation and dose titration.

Clonidine, a centrally acting adrenergic drug, can suppress autonomic symptoms and signs of opioid withdrawal. Starting dosages are 0.1 mg orally every 4 to 6 hours and may be increased to 0.2 mg orally every 4 to 6 hours as tolerated. Clonidine can cause hypotension and drowsiness, and its withdrawal may precipitate restlessness, insomnia, irritability, tachycardia, and headache.

Rapid and ultrarapid protocols have been evaluated for managing withdrawal and detoxification. In rapid protocols, combinations of naloxone, nalmefene, and naltrexone are used to induce withdrawal, and clonidine and various adjuvant drugs are used to suppress withdrawal symptoms. Some rapid protocols use buprenorphine to suppress opioid withdrawal symptoms. Ultrarapid protocols may use large boluses of naloxone and diuretics to enhance excretion of the opioids while patients are under general anesthesia; these ultrarapid protocols are not recommended because they have a high risk of complications and no substantial additional benefit.

Clinicians must understand that detoxification is not treatment per se. It is only the first step and must be followed by an ongoing treatment program, which may involve various kinds of counseling and possibly nonopioid antagonists (eg, naltrexone).

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  • Substance Abuse and Mental Health Services Administration (SAMHSA): US Department of Health agency that leads public health efforts to improve behavioral health and provides resources, including treatment locators, toll-free helplines, practitioner training tools, statistics, and publications on a variety of substance-related topics.

  • Listing of licensed US providers of treatment for substance use disorders.

Drugs Mentioned In This Article

Drug Name Select Trade
EVZIO, Kloxxado, Narcan, ZIMHI
Dolophine, Methadose
Belbuca, Brixadi, Buprenex, Butrans, Probuphine, Sublocade, Subutex
Depade, ReVia, Vivitrol
Sclerosol, STERITALC
ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T
Demerol, Meperitab
ABSTRAL, Actiq, Duragesic, Fentora, IONSYS, Lazanda, Onsolis, Sublimaze, SUBSYS
ConZip, QDOLO, Rybix, Ryzolt, Ultram, Ultram ER
No brand name available
Dazidox , Endocodone , ETH-Oxydose, Oxaydo, OXECTA, OxyContin, Oxydose , OxyFast, OxyIR, Percolone, Roxicodone, Roxybond, XTAMPZA
Catapres, Catapres-TTS, Duraclon, Kapvay, NEXICLON XR
OPVEE, Revex
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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