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Long-acting μ-opioid antagonist

Naltrexone hydrochloride

Brand names: Adepend, Nalorex

Naltrexone hydrochloride is an opioid receptor antagonist used as an adjunct to prevent relapse in formerly opioid-dependent people who have been detoxified, and also used to support abstinence in alcohol dependence.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It competitively blocks mu opioid receptors, abolishing the rewarding effects of opioids and attenuating the reinforcing, reward-related effects of alcohol mediated through the endogenous opioid system.

Prescribing in practice

  • Patients must be free of opioids before initiation, otherwise an acute and severe withdrawal syndrome can be precipitated.
  • It blocks the effect of opioid analgesics and raises the risk of fatal overdose if a relapsed patient takes opioids after losing tolerance.
  • Check liver function before and during treatment, and use with caution in hepatic or renal impairment.

Monitoring

Monitor liver function before and during treatment, and review abstinence, adherence and engagement with psychosocial support at regular intervals.

Counselling the patient

  • Avoid all opioids while taking this medicine and tell clinicians you take an opioid blocker before any surgery or strong painkillers.
  • It is most effective as part of a wider programme of psychological and social support.
  • Report persistent abdominal pain, dark urine or yellowing of the skin or eyes.

Evidence & guidelines

NICE supports naltrexone as an adjunct, with psychosocial support, for relapse prevention in opioid dependence and as an option for maintaining abstinence in alcohol dependence.

Reference: NICE CG115; PHE drug misuse guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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