Methadone

Opioid analgesic (full mu-agonist), NMDA receptor antagonist, Schedule II controlled substance

Methadone

Dolophine, Methadose, Diskets (oral dispersible tablets for OTPs)

Methadone, marketed as Dolophine and Methadose, is a long-acting synthetic full mu-opioid receptor agonist with NMDA antagonist activity, used for chronic pain management and as the original medication for opioid use disorder (MOUD). It was synthesized in Germany during World War II by chemists at IG Farben (Adolf Eisleb, Otto Schaumann, Max Bockmuhl) as Hoechst 10820, originally called Polamidon and intended as an analgesic to address wartime morphine shortages. It reached the United States after the war via Eli Lilly and was FDA-approved in 1947. The 1965 Dole and Nyswander studies at Rockefeller University established methadone maintenance as an effective treatment for heroin addiction, founding the modern MOUD field. Methadone differs from short-acting opioids in three pharmacologically important ways: a very long elimination half-life (8-59 hours, mean ~24 hours) that supports once-daily dosing for OUD but creates accumulation risk in pain titration; NMDA antagonist activity that may attenuate opioid tolerance and contribute to efficacy in neuropathic pain; and dose-dependent QTc prolongation that requires cardiac monitoring at higher doses.

History

The compound that became methadone was synthesized in 1937-1939 at IG Farben in Hochst (now part of Sanofi) by Adolf Eisleb, Otto Schaumann, and Max Bockmuhl, originally as Hoechst 10820. The synthesis was driven by Germany's wartime morphine supply concerns and was intended as a synthetic analgesic alternative. The compound was tested clinically in Germany under the name Polamidon during World War II. After the war, the United States Department of Commerce Technical Industrial Intelligence Committee inventoried the German pharmaceutical research; methadone reached the United States via Eli Lilly, which received the patents and trial data as part of the German pharmaceutical industry's post-war reparations. FDA approval as Dolophine followed in 1947 for severe pain.

In 1964, Vincent Dole and Marie Nyswander at Rockefeller University in New York began a clinical trial in which heroin-dependent patients were maintained on stable daily doses of methadone. The 1965 and 1966 papers establishing methadone maintenance treatment as effective for OUD founded the modern field of medication-assisted treatment.^{[citation needed]} The original methadone maintenance treatment programs were established in New York City in the late 1960s; the federal OTP regulatory framework (the Methadone Regulations under 21 CFR Part 291, later 42 CFR Part 8) was promulgated in 1972 and constrains how methadone for OUD is dispensed in the United States to this day.

The FDA added the QT prolongation boxed warning in November 2006 following accumulated reports of torsades de pointes and sudden cardiac death in methadone-treated patients. Subsequent guidelines (Krantz et al 2009 Annals of Internal Medicine) provided clinical decision frameworks for ECG monitoring.^{[citation needed]}

The DEA X-waiver requirement for buprenorphine prescribing was abolished by the Mainstreaming Addiction Treatment (MAT) Act passed in December 2022 and implemented in 2023; however, the OTP restriction for methadone-MOUD dispensing remains federally in place, with limited recent expansion of take-home flexibility post-COVID.

Experience

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Problems

Chronic pain★★★★★★★★★★★★★★★—××

Chronic pain when alternative treatments are inadequate; specifically valued in opioid-tolerant patients (NMDA blockade attenuates tolerance) and in neuropathic pain syndromes.

Opioid Use Disorder★★★★★★★★★★★★★★★—××

Opioid use disorder; the original MOUD agent. Dispensing in US is restricted to FDA-certified Opioid Treatment Programs (OTPs) federally.

<problem>: unknown ref "neonatal-abstinence"

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Titration strategies

Chronic pain, opioid-naive▲0▼×

Start 2.5-5 mg PO every 8-12 hours. Increase by no more than 25-50% every 5-7 days based on response and accumulation profile. Pain control may lag drug accumulation; counsel patient on the latency. Steady state requires 5-7 days at any given dose. Conversions from other opioids use a NON-LINEAR ratio that is substantially LOWER than published equianalgesic tables suggest, especially at higher pre-conversion opioid doses; specialist consultation advised for conversion.

MOUD induction (OTP setting)▲0▼×

Day 1: 20-30 mg PO once daily. Re-evaluate at 2-4 hours; may give additional 5-10 mg if withdrawal incomplete (cumulative day 1 dose typically not exceeding 40 mg). Days 2-7: increase by 5-10 mg every 1-3 days as tolerated; target dose typically 60-120 mg/day at steady state. Accumulation over the first week is the dominant safety concern.

MOUD maintenance▲0▼×

Typical effective range 60-120 mg/day as single daily dose, though some patients require higher doses for adequate craving and withdrawal suppression. Plasma trough concentrations can guide individualization in difficult cases. Withdrawal symptoms returning before next dose suggests under-dose or rapid metabolism (CYP2B6 UM phenotype consideration).

Hepatic impairment▲0▼×

Reduce starting dose by 25-50% and titrate slowly. Substantial CYP-mediated metabolism means hepatic dysfunction prolongs half-life; cirrhosis particularly extends exposure.

Elderly▲0▼×

Start at the low end (2.5 mg) with longer intervals between titrations. Clearance reduced; QT risk elevated. Fall risk substantial.

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Effects

• <effect>: unknown ref "analgesia"
• <effect>: unknown ref "sedation"
• Constipation👤 no reports yet⚕️ no reports yetRate×

  Universal; prophylactic bowel regimen recommended.
• Respiratory depression👤 no reports yet⚕️ no reports yetRate×

  Dose-dependent; the central safety pivot, especially in opioid-naive patients and with benzodiazepine / alcohol / other CNS depressant combination.
• QT prolongation👤 no reports yet⚕️ no reports yetRate×

  Dose-dependent; mechanism is hERG K+ channel block. ECG monitoring recommended at baseline, after dose changes, and at doses >100 mg/day.
• <effect>: unknown ref "torsades-de-pointes"
• <effect>: unknown ref "hypotension"
• Sweating / diaphoresis👤 no reports yet⚕️ no reports yetRate×

  Notably common with methadone, often described as severe.
• <effect>: unknown ref "hypogonadism"
• Weight gain👤 no reports yet⚕️ no reports yetRate×

  Common in MOUD maintenance; partly metabolic, partly improved nutrition with stable life circumstances.
• <effect>: unknown ref "dental-caries"
• <effect>: unknown ref "opioid-withdrawal"

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Pharmacokinetics

Absorption

Oral bioavailability ~70-85% (high for an opioid). Peak plasma 2-4 hours after oral dose. Distribution from plasma to tissue is rapid; redistribution into deep tissue compartments contributes to the long elimination phase.

Distribution

Plasma protein binding 85-90%, primarily to alpha-1-acid glycoprotein (which can be inducible in inflammatory states, modestly affecting free fraction). Volume of distribution 1-8 L/kg (highly variable). Crosses blood-brain barrier and placenta readily; excreted in breast milk at low levels generally considered compatible with breastfeeding in stable maintained patients.

Metabolism

Hepatic N-demethylation primarily via CYP3A4 and CYP2B6, with minor CYP2D6 and CYP2C19 contributions. Metabolites are inactive. Methadone is itself a weak CYP3A4 inhibitor (clinically modest). The dominant clinical PK fact is high interindividual variability in clearance (CYP2B6 polymorphism is a major contributor); the same daily dose can produce 10-fold differences in steady-state plasma concentrations between patients.

Elimination

Predominantly renal as inactive metabolites (~33%) and biliary (~33%); ~33% unchanged in feces. Urinary pH affects clearance modestly: acidic urine accelerates excretion of the parent compound (weak base ion-trapping). Mean half-life ~22-24 hours; range 8-59 hours.

Pharmacodynamics

Methadone is a full mu-opioid receptor agonist with intrinsic activity comparable to morphine; the long receptor residency time relative to morphine contributes to the prolonged analgesic and withdrawal-suppression effect. The NMDA receptor antagonist activity is the distinguishing pharmacodynamic feature: methadone blocks the NMDA glutamate receptor at clinically relevant concentrations (Ki ~7-30 micromolar), and this NMDA blockade is one proposed mechanism for methadone's efficacy in opioid-tolerant patients (NMDA receptors contribute to opioid tolerance development) and in neuropathic pain syndromes where NMDA signaling contributes to central sensitization. Weak serotonin and norepinephrine reuptake inhibition adds a modest non-opioid analgesic component but also contributes to serotonin syndrome risk with serotonergic comedications.

QTc prolongation is mediated by hERG (Kv11.1) potassium channel block; the dose-response is clinically meaningful above 100 mg/day in many patients and at lower doses in those with hypokalemia, hypomagnesemia, hepatic dysfunction, female sex, or concurrent QT-prolonging medications.

Interactions

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The clinically important interactions for prescribers:

• Other CNS depressants (boxed warning). Benzodiazepines, alcohol, sedating antihistamines, gabapentinoids, sleep aids: additive respiratory depression. Benzodiazepine + methadone is the most common pharmacological contributor to opioid overdose deaths in MOUD populations; the FDA explicitly does not recommend withholding methadone MOUD from patients also on benzodiazepines, but counseling and monitoring are essential.
• QT-prolonging medications. Class IA and III antiarrhythmics, certain antibiotics (macrolides, fluoroquinolones), antifungals, neuroleptics (especially haloperidol IV), SSRIs (citalopram > others), tricyclics, antiemetics (ondansetron, droperidol). Baseline + follow-up ECG monitoring; consider alternative when feasible.
• CYP3A4 strong inhibitors. Ritonavir, clarithromycin, ketoconazole, itraconazole, voriconazole: substantial methadone exposure increase; reduce methadone dose and monitor.
• CYP3A4 strong inducers. Rifampin, phenytoin, phenobarbital, carbamazepine, efavirenz, nevirapine, St John's wort: substantial methadone exposure decrease; methadone withdrawal can emerge within days. Dose increase typically required.
• CYP2B6 inhibitors and inducers. Sertraline raises methadone levels approximately 26% over six weeks via CYP2B6 inhibition, with stereoselective accumulation of the QT-prolonging (S)-methadone enantiomer.^{[citation needed]}
• Serotonergic medications. SSRIs, SNRIs, MAOIs, tramadol, linezolid, IV methylene blue: serotonin syndrome risk via methadone's weak SRI / NRI activity. Documented but less common than with strongly serotonergic opioids (meperidine, tramadol).
• Other opioids. Mixed agonist-antagonists (buprenorphine, nalbuphine, butorphanol) precipitate withdrawal in methadone-maintained patients; never give without specialist guidance.
• Naloxone. Reverses opioid effect; in methadone overdose, repeat doses or continuous infusion needed due to the long methadone half-life.

  Pregnancy and lactation

Methadone has been the standard of care for opioid use disorder in pregnancy since the 1970s, established before formal regulatory approval. The maternal benefits (stable opioid exposure, removed from illicit supply variability, integration into prenatal care) substantially outweigh the neonatal abstinence syndrome (NAS) that follows third-trimester exposure. NAS is expected with chronic methadone exposure during pregnancy; management is supportive in the NICU with non-pharmacologic interventions (rooming-in, breastfeeding, swaddling) and opioid taper (typically with morphine or methadone) for severe cases.

Methadone clearance increases through pregnancy (probably via CYP3A4 induction), and many patients require dose increases or split daily dosing during the second and third trimesters. Postpartum dose reduction may be needed.

Buprenorphine is increasingly used as an alternative to methadone in pregnancy MOUD; the MOTHER trial (Jones et al 2010 NEJM) and subsequent data show comparable maternal outcomes and somewhat milder NAS with buprenorphine. ACOG (Committee Opinion 711) and ASAM endorse both methadone and buprenorphine as first-line options.^{[citation needed]}

Methadone is excreted into breast milk at low concentrations (M/P ratio approximately 0.6, infant exposure typically <3% of maternal weight-adjusted dose); ACOG and the Academy of Breastfeeding Medicine recommend breastfeeding for stable maintained patients.

Monitoring

Boxed warning items: addiction/abuse/misuse, respiratory depression, NAS, QT prolongation. The QT-prolongation monitoring is methadone-specific:

• Baseline ECG before starting methadone, especially in patients with cardiac risk factors, electrolyte abnormalities, or concurrent QT-prolonging medications.
• Follow-up ECG at 30 days and annually; sooner with dose increases above ~100 mg/day, with addition of QT-prolonging comedications, or with new cardiac symptoms.
• QTc threshold for intervention: >450 ms warrants caution and consideration of alternative; >500 ms warrants dose reduction or discontinuation and cardiology consultation.

Other monitoring:

• Daily clinical assessment during induction (first 7-14 days) for accumulation toxicity; rising sedation, slurred speech, or respiratory rate <12 = immediate hold.
• Electrolytes (K+, Mg++) periodically, especially with diuretics or GI losses.
• LFTs at baseline + periodically (hepatic dysfunction extends half-life substantially).
• Testosterone level in male patients with low libido or sexual dysfunction (opioid-induced hypogonadism is common and treatable).
• Dental examination at intake + annually for MOUD patients (xerostomia + caries risk).
• PDMP review at intake + regularly per state requirements.
• Urine drug screening per OTP regulation.

  Patient counseling

Accumulation safety (pain titration). Methadone keeps building up in your body for 5-7 days after each dose change. Pain control may not match the dose increase for a week. Do NOT take extra doses if pain is uncontrolled in the first days after a dose change; call your prescriber.

Benzodiazepines and alcohol (boxed warning). Combining methadone with benzodiazepines or alcohol substantially increases the risk of fatal overdose. If you are on a benzodiazepine, talk with your prescriber about whether you can safely taper it.

QT and the heart. Methadone can affect the heart's electrical conduction; this is dose-related. Tell your provider if you have a personal or family history of heart rhythm problems, sudden cardiac death, or unexplained fainting, and any new symptoms of dizziness, palpitations, or fainting on methadone.

Driving and machinery. Do not drive after starting methadone, after any dose increase, or if you feel sedated. Once stable on a steady dose with no sedation, most patients can drive safely.

Pregnancy. If you become pregnant on methadone, do NOT stop abruptly - this can harm the pregnancy. Methadone MOUD is the standard of care in pregnancy.

Naloxone awareness. Keep naloxone (Narcan) available at home and in your car. Educate household members to recognize opioid overdose and use naloxone. Because methadone is long-acting, repeat naloxone doses may be needed and emergency care is essential.

Constipation. Methadone almost always causes constipation. Start a bowel regimen (fiber, hydration, stool softener, plus a stimulant laxative if needed) before constipation becomes a problem.

Dental care. Methadone causes dry mouth which can lead to rapid tooth decay. Drink water frequently rather than sugared beverages. Brush twice daily with fluoride toothpaste, floss daily, and see a dentist at least annually.

Discontinuation. Never stop methadone abruptly after long-term use; talk with your prescriber about a slow taper. Withdrawal from methadone is protracted (weeks rather than days) compared to short-acting opioids.

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Relevant Literature

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See also

Buprenorphine, Morphine, Oxycodone, Naltrexone, Naloxone

References

Summary

Classes

Opioid analgesic (full mu-agonist), NMDA receptor antagonist, Schedule II controlled substance

Common uses

• Chronic pain★★★★★★★★★★★★★★★—×
• Opioid Use Disorder★★★★★★★★★★★★★★★—×

Pharmacy

Starting dose

Pain (opioid-naive): 2.5-5 mg PO every 8-12 hours; titrate cautiously (long half-life, accumulation over days). MOUD induction (OTP): 20-30 mg on day 1, increase by 5-10 mg per day to symptomatic comfort; maintenance typically 60-120 mg/day in single daily dose. Conversions from other opioids use a NON-LINEAR ratio (much lower than published equianalgesic tables suggest); consult specialist guidance

Preparations

Tablets 5, 10, 40 mg (40 mg dispersible restricted to OTPs); oral concentrate 10 mg/mL; oral solution 1, 2, 10 mg/mL; injection 10 mg/mL

US FDA Max

No formal hard ceiling; in MOUD maintenance, doses typically remain at or below 120 mg/day with higher doses reserved for documented under-treatment after careful clinical assessment

Pharmacology

Routes

Oral (primary), IV, IM, SC, sublingual; rectal off-label

Onset

Oral analgesic effect 30-60 minutes; opioid-withdrawal suppression 30 minutes (oral); IV ~10 minutes

Duration

Analgesic effect 4-8 hours (much shorter than half-life would suggest, due to receptor kinetics); MOUD effect (opioid withdrawal suppression) 24-36 hours per single daily dose

Half-life

Highly variable: 8-59 hours (mean ~22-24 hours; range due to CYP genetic variation + age + comorbidities). The discordance between long elimination half-life and shorter analgesic duration is the central dose-titration problem - patients can have inadequate pain control while methadone is still accumulating dangerously toward steady state.

Bioavailability

~70-85% (oral, high relative to other opioids)

Pregnancy

Methadone is a standard of care for opioid use disorder during pregnancy; the alternative (untreated OUD or unstable supply) carries substantially greater risks to mother and fetus. Neonatal abstinence syndrome (NAS) is expected with chronic third-trimester exposure; managed with non-pharmacologic supportive care + opioid taper (morphine or methadone) in NICU as needed. Buprenorphine is increasingly used as an alternative in pregnancy MOUD with comparable maternal outcomes and somewhat milder NAS. ACOG and ASAM endorse both.^{[citation needed]}

Legal status

Schedule II controlled substance in US. For chronic pain: prescribed by any DEA-licensed prescriber. For opioid use disorder: dispensing restricted to FDA-certified Opioid Treatment Programs (OTPs) federally (the DEA X-waiver for buprenorphine was abolished in 2023 but the OTP restriction for methadone MOUD continues, with limited recent expansion of take-home flexibility). Carries the opioid class Boxed Warning for addiction, abuse, misuse, life-threatening respiratory depression, neonatal abstinence syndrome, and life-threatening QT prolongation; the QT-prolongation warning is methadone-specific in scope.

Purported mechanism

Full mu-opioid receptor agonist (similar intrinsic activity to morphine but with longer receptor residency); NMDA receptor antagonist (the NMDA blockade is the distinguishing mechanistic feature that may contribute to its efficacy in opioid-tolerant patients and in chronic neuropathic pain); weak serotonin and norepinephrine reuptake inhibition. The long elimination half-life with relatively short analgesic duration produces a clinically distinctive accumulation pattern: pain may not be controlled at a given dose while drug is still building toward steady state over 5-7 days, creating dose-titration danger for inexperienced prescribers. Methadone is a CYP3A4 and CYP2B6 substrate, with minor CYP2D6 and CYP2C19 contributions; this complex metabolism produces highly variable interindividual half-lives and a substantial drug-interaction burden.▲0▼ QTc prolongation via hERG potassium channel block is dose-dependent and clinically meaningful; the FDA black box warning specifically calls for baseline and follow-up ECG monitoring at higher doses (typically beyond 100 mg/day) and in patients with cardiac risk factors or concurrent QT-prolonging medications.