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Methadone: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Feb 28, 2023.

1. How it works

  • Methadone is a man-made substance that may be used to reduce withdrawal symptoms in people addicted to heroin or other narcotic drugs as part of a drug addiction detoxification and maintenance program. It may also be used as a pain reliever.
  • Methadone acts on mu opioid receptors in a similar way to morphine to provide pain relief. It inhibits ascending pain pathways, altering the perception of and response to pain. It has also been shown to have N-methyl-D-aspartate (NMDA) receptor antagonism.
  • Methadone belongs to the class of medicines known as narcotic analgesics. It may also be called an opioid analgesic. An analgesic is a drug that is used to relieve pain. However, methadone is more commonly used in the treatment of opioid addiction.
  • Methadone is a schedule II controlled substance.

2. Upsides

  • Used for the treatment of pain severe enough to require continuous, round-the-clock treatment in patients unresponsive or intolerant of other opioid and nonopioid analgesics.
  • May be used under strict conditions for the treatment of opioid addiction disorders.
  • Withdrawal symptoms associated with methadone generally are less severe than with morphine and have a slower onset.
  • Generic methadone is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Sedation, drowsiness, or dizziness may affect a person's ability to drive or operate machinery. Alcohol should be avoided as it can contribute to the sedative effect of methadone.
  • Methadone tablets may cause serious, life-threatening respiratory depression (unusually shallow and slow breathing). More likely to occur in the elderly or frail, in children, or those with pre-existing breathing problems. This effect on breathing persists for longer and occurs later than the peak pain-relieving effects of methadone. Alcohol can also worsen this effect.
  • May also cause increased sweating, nausea, vomiting, headache, severe constipation, seizures, and several other adverse effects.
  • Because of the high risk of addiction and potential for abuse, methadone should only be used in patients intolerant or unresponsive to other analgesics (either opioid or nonopioid analgesics). Methadone is considered a drug of abuse and legitimate supplies may be sought out by drug users. Misuse of methadone may lead to overdosage or death.
  • May cause serious heart rhythm disorders (such as QT prolongation), even at usual dosages.
  • Use during pregnancy can cause a withdrawal syndrome in newborn babies which can be life-threatening if not recognized and treated.
  • May cause a severe lowering of blood pressure, or a sudden drop in blood pressure when going from a sitting or lying down position to standing.
  • May interact with several other drugs including other opioids, benzodiazepines, and other central nervous system depressants resulting in profound sedation, respiratory depression, and sometimes death. May also interact with drugs metabolized through many CYP hepatic enzyme systems or drugs that also release serotonin (such as antidepressants, antipsychotics, and tramadol).
  • Methadone accumulates within the liver and repeated dosing and overdosing may enhance its toxic effects. Although it only lasts for 4 to 8 hours, it can take up to 59 hours for 50% of a dose to be eliminated from the body.
  • Methadone has a narrow therapeutic window which means there is a fine line between too much methadone (and toxic effects) and too little (meaning it is ineffective). There is a wide variation in the way individuals absorb, metabolize, and respond to methadone, which increases the risk of a person receiving a toxic or ineffective dose. This means opioid equivalency charts should not be used when changing from an opioid to methadone and vice versa.
  • Methadone is only available from a certified pharmacy.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

  • Methadone is a potent opioid analgesic that may be used to relieve severe pain unresponsive to other strong pain relievers; however, it is more commonly used to treat opioid addiction. There is a wide variation in the way individuals respond to methadone, and there is a fine line between delivering a toxic dose and delivering an ineffective dose, which makes the dosing of methadone difficult.

5. Tips

  • Take it strictly as directed by your doctor. Do not use on an "as needed" basis or increase or decrease the dosage without your doctor's advice. There is a fine line between an effective dose of methadone and a toxic dose because of the high variability between patients in the absorption and metabolism of methadone and its analgesic effect.
  • If you are taking methadone for severe pain, tell your doctor if you begin to have breakthrough pain.
  • When used to treat drug addiction, it is important that you take advantage of any social support and counseling services offered to you as withdrawal from opioids is a long and often difficult process and a successful outcome is dependent upon a multi-targeted approach.
  • All other around-the-clock opioid drugs should be discontinued when starting methadone. Deaths have occurred in people who continue to take these.
  • Methadone has a REMS (Risk Evaluation and Mitigation Strategy) associated with it which means you will need to fill in a patient enrolment form with your Healthcare prescriber. Always read the medication guide prescribed with methadone.
  • Tell your doctor if you experience any difficulty with breathing or shortness of breath after taking methadone, especially within the first 24 to 72 hours of initiating therapy.
  • Avoid sudden discontinuation of methadone. The dosage of methadone must be tapered off slowly to minimize withdrawal symptoms which include restlessness, runny nose and eyes, muscle pain, and insomnia. When the time comes to discontinue methadone, your doctor will advise you on a tapering schedule.
  • Rise carefully from a sitting to a standing position to minimize blood pressure-lowering effects from methadone which may result in dizziness increasing your risk of falls.
  • Consider concomitant laxatives while taking methadone due to the risk of severe constipation. Talk with your health professional about which laxatives are the most effective to take with methadone. Tell your doctor if you develop any other side effects that are worrying or affecting your quality of life.
  • Always talk to your doctor or pharmacist before buying anything over-the-counter to check if it is compatible with methadone.
  • Accidental ingestion by children may be fatal. Keep out of reach of all children.

6. Response and effectiveness

  • The analgesic effect of methadone lasts between four and eight hours; however, it takes anywhere from eight to 59 hours for a dose to be eliminated from the body. With prolonged dosing, methadone is retained in the liver and then slowly released, prolonging how long it works and how long side effects may last. The full analgesic effects of methadone may take from three to five days to develop.
  • The peak respiratory depressant effect of methadone occurs later and persists for longer than its peak analgesic effect.

7. Interactions

Medicines that interact with methadone may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with methadone. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with methadone include:

  • antibiotics, such as erythromycin
  • antidepressants, such as tricyclic antidepressants (eg, amitriptyline), monoamine oxidase inhibitors (eg, isocarboxazid, phenelzine, and tranylcypromine), or SSRIs (eg, fluoxetine, sertraline)
  • antifungal agents, such as fluconazole, itraconazole, and ketoconazole
  • anticonvulsants, such as carbamazepine, lamotrigine, phenytoin, phenobarbital, or primidone
  • antiemetics such as ondansetron
  • antimigraine agents such as sumatriptan
  • antipsychotics (such as butyrophenones, phenothiazines, or thioxanthenes) and atypical antipsychotics (eg, olanzapine, quetiapine, ziprasidone)
  • any medication that inhibits or induces CYP3A4
  • any medication that may cause drowsiness, such as amphetamines, benzodiazepines (eg, diazepam, lorazepam), first-generation antihistamines (such as doxylamine or promethazine), metoclopramide, or opioids (such as codeine, morphine)
  • any medication that may prolong the QT interval such as amiodarone, flecainide, and procainamide
  • buprenorphine
  • diuretics such as furosemide
  • HIV medications such as ritonavir
  • muscle relaxants, such as cyclobenzaprine
  • naloxone and naltrexone
  • other medications such as those for glaucoma, Parkinson's disease, and urinary problems
  • rifampin
  • St. John's Wort.

Avoid drinking alcohol or taking illegal or recreational drugs while taking methadone.

Note that this list is not all-inclusive and includes only common medications that may interact with methadone. You should refer to the prescribing information for methadone for a complete list of interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use methadone only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: February 28, 2023.