Naltrexone

How it works

It competitively antagonises mu opioid receptors, blocking the euphoric and other effects of exogenous opioids and thereby removing their reinforcing reward.

Prescribing in practice

• The patient must be opioid-free and confirmed abstinent before starting, as giving it too soon precipitates a severe acute withdrawal reaction.
• It blocks opioid analgesia, so alternative pain management is needed and patients carry a heightened overdose risk if they relapse after tolerance has fallen.
• Assess liver function before and during treatment, and use cautiously in hepatic or renal impairment.

Monitoring

Check liver function before starting and periodically during treatment, and monitor abstinence, adherence and engagement with the wider treatment programme.

Counselling the patient

• Do not take any opioids while on this medicine; trying to overcome the block with large doses risks fatal overdose.
• Carry information that you take an opioid blocker in case you need emergency pain relief.
• Use it as part of a structured relapse-prevention programme with psychological support.

Evidence & guidelines

NICE recommends naltrexone as an option to help maintain abstinence in detoxified, formerly opioid-dependent people who are motivated to remain opioid-free.