Methadone Side Effects

Medically reviewed by Philip Thornton, DipPharm. Last updated on Mar 19, 2024.

Applies to methadone: injection solution.

Other dosage forms:

• oral solution, oral tablet, oral tablet for suspension

Important warnings This medicine can cause some serious health issues

Injection route (solution)

QT interval prolongation and serious arrhythmias (torsades de pointes) have been observed during treatment with methadone.

Only approved hospitals and pharmacies can dispense oral methadone for the treatment of narcotic addiction.

Methadone can be dispensed in any licensed pharmacy when used as an analgesic.

QT interval prolongation and serious arrhythmias (torsades de pointes) have been observed during treatment with methadone.

Most cases involve patients being treated with higher doses (greater than 200 mg/day), although cases have been reported in patients receiving doses commonly used for maintenance treatment of opioid addiction.

Serious side effects of methadone

Along with its needed effects, methadone may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor or nurse immediately if any of the following side effects occur while taking methadone:

Incidence not known

• agitation
• blurred vision
• confusion
• darkening of the skin
• diarrhea
• difficult or troubled breathing
• dizziness
• dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
• fainting
• fever
• irregular heartbeat
• recurrent irregular, fast or slow, or shallow breathing
• loss of appetite
• mental depression
• nausea
• overactive reflexes
• pale or blue lips, fingernails, or skin
• poor coordination
• restlessness
• seizures
• shivering
• skin rash
• sweating
• talking or acting with excitement you cannot control
• trembling or shaking
• twitching
• unusual tiredness or weakness
• vomiting

Other side effects of methadone

Some side effects of methadone may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

• bleeding, blistering, burning, coldness, discoloration of the kin, feeling of pressure, hives, infection, inflammation, itching, lumps, numbness, pain, rash, redness, scarring, soreness, stinging, swelling, tenderness, tingling, ulceration, or warmth at the injection site
• difficulty having a bowel movement (stool)
• dry mouth
• headache
• lack or loss of strength
• loss of appetite
• weight loss

For healthcare professionals

Applies to methadone: compounding powder, injectable solution, intravenous solution, oral concentrate, oral solution, oral tablet, oral tablet dispersible.

General adverse events

The major adverse reaction of this drug is respiratory depression; to a lesser degree, systemic hypotension, respiratory arrest, shock, cardiac arrest, and death have occurred. The most commonly observed adverse reactions include lightheadedness, dizziness, sedation, nausea, vomiting, and sweating.^[Ref]

Cardiovascular

• Common (1% to 10%): Edema
• Uncommon (0.1% to 1%): Syncope, flushing, hypotension
• Rare (less than 0.1%): Bradycardia, palpitations, QT interval prolongation, Torsades de pointes
• Frequency not reported: Arrhythmias, bigeminal rhythms, cardiomyopathy, ECG abnormalities, extrasystoles, heart failure, phlebitis, QT interval prolongation, syncope, T-wave inversion, tachycardia, ventricular fibrillation, ventricular tachycardia^[Ref]

Cases of QT interval prolongation and Torsades de pointes have occurred during treatment; these cases appear to be more commonly associated with higher dose treatment (greater than 200 mg per day). There have been some cases in patients receiving lower doses and in these cases contributing factors such as concomitant medications and/or clinical conditions were present. In vivo studies have confirmed this drug effects the QT interval and in vitro studies have shown it inhibits cardiac potassium channels.^[Ref]

Gastrointestinal

• Very common (10% or more): Nausea, vomiting
• Common (1% to 10%): Constipation
• Uncommon (0.1% to 1%): Dry mouth, glossitis
• Frequency not reported: Abdominal pain, anorexia, biliary tract spasm^[Ref]

Constipation often persists during chronic administration; nausea, and vomiting appear to be more frequent after oral administration.^[Ref]

Other

• Common (1% to 10%): Vertigo, fatigue
• Uncommon (0.1% to 1%): Asthenia, hypothermia^[Ref]

Hypersensitivity

• Frequency not reported: Anaphylaxis^[Ref]

Anaphylaxis has been reported with ingredients contained in methadone products.^[Ref]

Psychiatric

• Common (1% to 10%): Euphoria, hallucinations
• Frequency not reported: Agitation, dysphoria, insomnia, mood changes^[Ref]

Endocrine

• Uncommon (0.1% to 1%): Galactorrhea, dysmenorrhea, amenorrhea
• Frequency not reported: Hypogonadism, decreased serum testosterone, reduced libido and/or potency, reduced ejaculate volume, reduced seminal vesicle and prostate secretions, decreased sperm motility, abnormalities in sperm morphology, gynecomastia, adrenal insufficiency, increased prolactin concentrations^[Ref]

Hypogonadism, decreased serum testosterone, and reproductive effects are thought to be related to chronic opioid use.^[Ref]

Genitourinary

• Uncommon (0.1% to 1%): Urinary retention
• Frequency not reported: Urinary hesitancy, ureteric spasm^[Ref]

Respiratory

• Uncommon (0.1% to 1%): Pulmonary edema, exacerbation of asthma, dry nose, respiratory depression
• Frequency not reported: Pulmonary edema^[Ref]

Renal

• Uncommon (0.1% to 1%): Antidiuretic effect^[Ref]

Hematologic

• Frequency not reported: Reversible thrombocytopenia, lymphocytosis^[Ref]

Reversible thrombocytopenia has been described in opioid addicts with chronic hepatitis.^[Ref]

Nervous system

• Common (1% to 10%): Sedation, drowsiness
• Frequency not reported: Headache, seizures, confusion, disorientation, lightheadedness, agitation, confusion, disorientation, dysphoria, euphoria, insomnia, hallucinations, seizures^[Ref]

Metabolic

• Common (1% to 10%): Weight gain
• Frequency not reported: Hypokalemia, hypomagnesemia^[Ref]

Ocular

• Common (1% to 10%): Miosis, dry eyes
• Frequency not reported: Visual disturbances, congenital oculomotor disorders (nystagmus, strabismus)^[Ref]

Dermatologic

• Common (1% to 10%): Transient rash, sweating
• Uncommon (0.1% to 1%): Pruritus, urticaria, other skin rashes
• Rare (less than 0.1%): Hemorrhagic urticaria^[Ref]

Sweating often persists during chronic administration.^[Ref]

Hepatic

• Uncommon (0.1% to 1%): Bile duct dyskinesia^[Ref]

Local

• Frequency not reported: Local tissue reactions (pain, erythema, swelling) particularly with continuous subcutaneous infusion^[Ref]

Frequently asked questions

• Which drugs cause opioid-induced constipation?
• How long does opioid withdrawal last?
• How can I get emergency methadone?
• Suboxone vs methadone: What’s the difference?
• How long does methadone withdrawal last?
• Does methadone show up on a drug test?
• Is methadone an opiate blocker?
• What is a methadone clinic / are they free?

Further information

Methadone side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer