Methadone

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

- Drowsiness
- Nausea and vomiting
- Dry mouth
- Constipation
- Difficulty passing urine
- Slow, shallow breathing (respiratory depression)
- Low blood pressure (hypotension)
- Feeling of unease, restlessness, agitation or being unwell
- False perceptions of things that are not really there (hallucinations)
- Mood changes
- Decreased heart rate
- Awareness of your heartbeat (palpitations)
- Rash or itching
- Decreased sex drive
- Contracted (pinpoint) pupils
- Addiction to the medicine (dependence)
- Excessive sweating
- Abnormal heartbeats (arrhythmias)

The side effects listed above may not include all of the side effects reported by the drug's manufacturer. For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

Methadone should not be taken by people who have taken a monoamine oxidase inhibitor (MAOI) in the last 14 days. MAOIs include the antidepressants phenelzine, isocarboxazid, tranylcypromine and moclobemide.

There may be an increased risk of side effects such as drowsiness, sedation, low blood pressure and slow, shallow breathing that can potentially be fatal, if this medicine is used with other medicines that have a sedative effect on the central nervous system. These include the following and should be avoided while taking this medicine:

- alcohol
- antipsychotics, eg haloperidol
- barbiturates, eg phenobarbital, amobarbital
- benzodiazepines, eg diazepam, temazepam
- other opioid painkillers, eg codeine, morphine
- sedating antihistamines, eg chlorphenamine, hydroxyzine
- sleeping tablets, eg zopiclone
- tricyclic antidepressants, eg amitriptyline.

The following medicines there may increase the blood level of methadone and thus increase the risk of its side effects:

- azole antifungals, eg itraconazole, ketoconazole, fluconazole, voriconazole
- cimetidine
- ciprofloxacin
- SSRI antidepressants, eg fluvoxamine, fluoxetine, sertraline
- macrolide antibiotics, eg erythromycin, clarithromycin.

The following medicines may reduce the blood level of methadone and so could cause withdrawal symptoms if given to someone addicted to methadone:

- antiretrovirals for HIV infection, eg nelfinavir, ritonavir, nevirapine, efavirenz
- carbamazepine
- phenobarbital
- phenytoin
- primidone
- rifampicin.

The following medicines antagonise the effects of methadone and can cause withdrawal symptoms if given to someone addicted to methadone:

- buprenorphine
- naltrexone
- naloxone
- pentazocine.

There may be an increased risk of abnormal heartbeats (seen on an ECG as a 'prolonged QT interval') if methadone is taken in combination with other medicines that can also potentially cause this problem, such as the following:

- cisapride
- certain medicines to treat abnormal heartbeats (antiarrhythmics), eg amiodarone, procainamide, quinidine, disopyramide, sotalol
- certain antidepressants, eg amitriptyline, imipramine, maprotiline
- certain antipsychotics, eg haloperidol, chlorpromazine, sertindole, thioridazine, pimozide
- certain antimalarials, eg quinine, mefloquine, chloroquine
- certain other anti-infectives, eg erythromycin, telithromycin, voriconazole, pentamidine
- terfenadine.

There may also be an increased risk of abnormal heartbeats if methadone is taken in combination with medicines that can cause disturbances in the levels of electrolytes (eg potassium and magnesium) in the blood, for example diuretics.

Other medicines containing the same active ingredient

Methadose

Physeptone

Synastone

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