Methadone — NZ Medication Guide

What is Methadone?

Methadone (generic name: methadone hydrochloride) is a medication used primarily for opioid dependence treatment (opioid substitution therapy) and severe chronic pain. Methadone oral liquid is funded by Pharmac under a strict controlled programme. Prescribing requires addiction medicine specialist involvement and community pharmacy supervised consumption.

What is Methadone Used For?

Methadone is prescribed by healthcare professionals in New Zealand for the following indications:

• Opioid use disorder — maintenance treatment (opioid substitution therapy, OST)
• Severe chronic pain not manageable with other opioids
• Cancer pain management
• Opioid detoxification programmes

How Does Methadone Work?

Methadone is a synthetic full opioid agonist that binds to mu-opioid receptors, relieving pain and suppressing opioid withdrawal symptoms and cravings. Unlike short-acting opioids, methadone has a very long half-life (24–36 hours), providing sustained receptor occupancy and stable blood levels. It also has NMDA receptor antagonist properties useful in chronic pain management.

How to Take Methadone

For opioid substitution therapy: methadone is dispensed as a supervised daily oral liquid from a community pharmacy or addiction clinic. Dose is individualised and titrated under specialist supervision. For pain management: prescribed by specialist or palliative care teams only. Never adjust the dose or share methadone — overdose risk is high, particularly during initiation and dose changes.

Common Side Effects

• Constipation (very common with long-term use)
• Sweating
• Drowsiness or sedation
• Nausea and vomiting (especially during initiation)
• Dry mouth
• QTc interval prolongation (cardiac — ECG monitoring required)

Serious Side Effects — Seek Medical Attention

• Respiratory depression — particularly during dose initiation or increases
• Overdose — unconsciousness, blue lips, slow or absent breathing — call 111
• Cardiac arrhythmia (torsades de pointes) due to QTc prolongation
• Severe withdrawal if dose suddenly stopped
• Dangerous sedation with other CNS depressants

Drug Interactions

• Benzodiazepines and alcohol — FATAL respiratory depression risk; extremely dangerous combination
• QTc-prolonging medications (antipsychotics, some antibiotics) — additive cardiac risk; ECG monitoring required
• CYP3A4 inducers (rifampicin, carbamazepine) — reduce methadone levels; precipitate withdrawal
• CYP3A4 inhibitors (fluconazole, erythromycin) — increase methadone levels; overdose risk
• Naloxone — precipitates acute withdrawal (avoid unless treating overdose)

New Zealand Prescribing Information

The NZ Opioid Substitution Treatment (OST) programme is co-ordinated through regional addiction services. Methadone is the most commonly used OST medication in NZ. Prescribers must hold a specific controlled drug licence. The Drug Foundation NZ advocates for OST access as a proven harm reduction intervention. A baseline ECG and QTc assessment is recommended before starting due to cardiac effects.

Frequently Asked Questions

Is methadone treatment just replacing one addiction with another?

This is a misconception. Methadone maintenance is evidence-based medical treatment that stabilises brain chemistry, prevents life-threatening withdrawal, and reduces illicit drug use and associated harms. The NZ Drug Foundation and Ministry of Health recognise OST as a fundamental harm reduction and public health intervention.

Why must I attend the pharmacy every day for methadone?

Daily supervised consumption ensures correct dosing, monitors for side effects, and prevents diversion. As you demonstrate stability (usually over several months), your prescriber can arrange take-home doses for progressively longer periods — a graduated approach to support your recovery journey.

References & Further Information

The following New Zealand and international resources were used to inform this page:

• New Zealand Formulary — Methadone
• NZ Drug Foundation — Opioid Substitution Treatment
• Ministry of Health NZ — OST Guidelines
• Pharmac — Funded Medicines Schedule

Reviewed by a Registered Pharmacist — KiwiMeds New Zealand