Naltrexone — NZ Medication Guide

📋 Reviewed by a Registered Pharmacist NZ — This information is for general educational purposes only and does not replace professional medical advice. Always consult your doctor or pharmacist before starting, stopping, or changing any medication.

What is Naltrexone?

Naltrexone is an opioid receptor antagonist supporting abstinence in opioid and alcohol use disorders. This medication is funded by Pharmac for opioid and alcohol use disorder.

What is Naltrexone Used For?

Used for relapse prevention in opioid dependence (following detoxification) and alcohol use disorder — reducing cravings and the rewarding effects of substances.

How Does Naltrexone Work?

Blocks opioid receptors, preventing the euphoric reinforcing effects of opioids and alcohol (which releases endogenous opioids via reward pathways). Without reinforcement, cravings and relapse risk reduce.

How to Take Naltrexone

50 mg daily for opioid or alcohol dependence. Must be opioid-free for at least 7–10 days before starting (longer for methadone). A test dose of 25 mg may be given first to check for withdrawal.

Common Side Effects of Naltrexone

• Nausea (common initially — take with food)
• Headache
• Fatigue
• Abdominal discomfort
• Dizziness

Serious Side Effects — Seek Medical Attention

Contact your doctor or call 111 immediately if you experience any of the following:

• Precipitated opioid withdrawal (if opioids not fully cleared — severe — do not start if still opioid-dependent)
• Hepatotoxicity (rare at standard doses)
• Depression (may exacerbate in some patients)

Drug Interactions

Naltrexone may interact with other medicines. Always inform your doctor and pharmacist of all medications you are taking. Key interactions include:

• Opioid medicines (blocks all opioid efficacy — standard doses cannot provide pain relief)
• Disulfiram (possible increased hepatotoxicity — caution)

New Zealand Prescribing Information

Naltrexone (Revia® 50 mg tablets) is funded by Pharmac as part of structured addiction treatment. Patients must be counselled that standard opioid analgesics will not work while on naltrexone — emergency pain management requires non-opioid analgesics or specialist anaesthetic involvement. Always inform every treating clinician and anaesthetist you are on naltrexone.

Frequently Asked Questions

Can I take pain medicines while on naltrexone?

Naltrexone blocks opioid receptors, making standard opioid painkillers ineffective. Use non-opioid analgesics for pain. In emergency situations requiring opioids, very high doses under strict specialist supervision can overcome the block — always inform your medical team you are on naltrexone.

How long does naltrexone take to work for alcohol cravings?

Naltrexone works best as part of a comprehensive programme including psychological support. Some reduction in cravings may be noticed within weeks, with full benefit over months of consistent treatment and engagement with support services.

References & Further Information

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

• New Zealand Formulary — Naltrexone
• BPAC NZ — Alcohol Use Disorder
• Pharmac — Funded Medicines Schedule

⚠️ Disclaimer: This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or a qualified health provider. In New Zealand, medication availability and funding may vary — check with Pharmac or your pharmacist for current information.

Reviewed by a Registered Pharmacist NZ