Methadone
Methadone is a synthetic opioid analgesic of the diphenylheptane class.1 First developed in Germany in 1937 by Gustav Ehrhart and Max Bockmühl, it is primarily used for the management of severe pain and as a maintenance therapy for opioid dependence.2 It is distinguished from other opioids by its comparatively long duration of action, good oral bioavailability, and additional activity as an NMDA receptor antagonist.3 It shares the typical risks associated with other opioids such as morphine and fentanyl.1
Contents
Dosage & Duration
Dosage
Methadone has a long and variable half-life. Do not re-dose within several hours, as peak effects and full absorption may be delayed. Clinical OAT typically uses doses of 40-100 mg daily.
Duration
Subjective Effects
Methadone produces a classic opioid experience centered on heavy sedation, pain relief, and a calm, contented mood, though its euphoria is generally considered muted and slower in onset compared to shorter-acting opioids such as heroin or oxycodone. First-hand accounts describe a mild, heady inebriation that retains far more mental clarity than alcohol, sometimes characterized as a lucid or sober intoxication in which the user remains largely in control of themselves. A pronounced anxiolytic undercurrent runs throughout the experience, with anxiety extinguished early and a stable, tranquil state persisting for many hours in keeping with the drug's exceptionally long duration. The experience typically resolves into tiredness and an earlier-than-usual readiness for sleep.
Physical
The body load is dominated by relaxation, sedation, and analgesia, accompanied by a gentle body warmth. Typical opioid side effects are prominent, including itching, constipation, pupil constriction, dry mouth, sweating, nausea, and at higher doses dangerous respiratory depression.
Autonomic
Cardiovascular
Perception
Sedation
Sedation is a core feature, presenting as a heady, mellow inebriation that transitions into drowsiness and fatigue over the long duration.
Cognitive
The headspace is tranquil, contented, and notably anxiolytic, with a mellow inebriation that preserves clarity at common doses and shifts toward a more zoned-out, less clear state as effects deepen. Mood is reliably lifted, though full-blown euphoria is not guaranteed, and memory impairment and disorientation can occur.
Emotional
The emotional tone is warm, calm, and contented rather than intensely euphoric.
Suppressions
Visual
Visual effects are limited to suppressions, primarily blurred vision.
Reagent Testing
Loading reagent data
Pharmacology
Pharmacodynamics
Methadone acts primarily as a full agonist at the μ-opioid receptor, mimicking the activity of endogenous endorphins.3 In the racemic mixture, the (R)-enantiomer carries the bulk of opioid activity, with roughly 10-fold higher μ-opioid affinity than the (S)-enantiomer.3 Methadone also activates κ-opioid, δ-opioid, and σ receptors.3 Beyond opioid targets, it antagonizes the NMDA glutamate receptor, dampening a major excitatory pathway in the central nervous system.43 It further acts as a weak serotonin and norepinephrine reuptake inhibitor, antagonizes 5-HT3A receptors and several nicotinic acetylcholine receptor subtypes (notably α3β4 and α4β2), and functions as an agonist at the α7 nicotinic acetylcholine receptor.
Pharmacokinetics
Methadone undergoes extensive first-pass metabolism in the liver, with oral bioavailability ranging widely from 36% to 100% due to marked interindividual variation.35 The primary metabolic pathway involves sequential N-demethylation, catalyzed mainly by CYP3A4 and CYP2B6, with additional contributions from CYP2C19, CYP2C9, CYP2C8, and CYP2D6.3 Methadone is also a substrate of P-glycoprotein, an efflux transporter expressed in the intestines and brain. Its high lipid solubility contributes to a prolonged and highly variable elimination half-life, typically 15 to 60 hours (mean approximately 22 hours), though individual values can span from as few as 4 hours to as many as 190 hours due to genetic variability in cytochrome P450 enzyme activity.35
Dangerous
Highest riskThese combinations are considered extremely harmful and should always be avoided. Reactions to these drugs taken in combination are highly unpredictable and have a potential to cause death.
Unsafe
AvoidThere is considerable risk of physical harm when taking these combinations, they should be avoided where possible.
Caution
Use cautionThese combinations are not usually physically harmful, but may produce undesirable effects, such as physical discomfort or overstimulation. Extreme use may cause physical health issues. Synergistic effects may be unpredictable. Care should be taken when choosing to use this combination.
Tolerance
Opioids (incomplete cross-tolerance; patients tolerant to other μ-opioid agonists may be incompletely tolerant to methadone, complicating dose conversion and creating overdose risk)
Harm Potential
Addiction & Dependence
Psychological
Extremely HighChronic use of methadone is considered extremely addictive with a high potential for abuse, comparable to morphine.6 It is capable of causing psychological dependence, with cravings developing when regular use is established.
Physical
HighPhysical dependence develops with repeated administration through neuroadaptation of opioid receptors.7 Withdrawal symptoms are reported as significantly more protracted than other opioids due to methadone's long half-life, and include body aches, diarrhea, nausea, anxiety, tremors, tachycardia, sweating, insomnia, fever, and elevated pain sensitivity.76
Toxicity
Long-term use is associated with impaired male reproductive function, including decreased testosterone levels, reduced sperm motility and morphology, reduced ejaculate volume, and decreased libido.10
Chronic use is associated with significant tooth decay due to dry mouth (xerostomia), which reduces saliva's protective role against decay; behavioral factors such as opioid-related carbohydrate cravings and reduced dental hygiene may contribute.11
Injection of oral methadone tablets containing talc filler can cause progressive, irreversible pulmonary hypertension due to particle accumulation in lung vasculature; this risk is specific to intravenous misuse of oral formulations.12
Psychosis Risk
Compared to other opioids, methadone has fewer active metabolites and therefore a lower risk of neuropsychiatric toxicity such as delirium at higher doses.13 However, withdrawal from methadone can cause cognitive symptoms including delirium, auditory and visual hallucinations, paranoia, and delusions.
Seizure Risk
Methadone is known to lower the seizure threshold.7 However, due to fewer active metabolites, higher doses are less likely to result in seizures compared to other opioids. Particular caution is warranted during benzodiazepine withdrawal as the combination may potentiate seizure risk.
History & Culture
Discovery and Development
Methadone was developed in 1937 in Germany by chemists Gustav Ehrhart and Max Bockmühl, working for I.G. Farbenindustrie AG at the Farbwerke Hoechst facility.14 The research was motivated by Germany's shortage of opium and morphine, creating demand for a synthetic…
Legality
International
1961 Single Convention on Narcotic Drugs: Schedule I
1971 Convention on Psychotropic Substances: not listed
1988 Convention against Illicit Traffic: not listed
By Country
South Carolina
References
Source Pages
Citations
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Further Reading
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