Long-acting μ-opioid antagonist Pregnancy: No clinical data on use in pregnancy; animal data have shown reproductive toxicity and the potential risk for humans is unknown. Should only be given to pregnant women when, in the judgement of the attending physician, the potential benefits outweigh the possible risk. Use in pregnant alcoholic patients receiving long-term or substitution treatment with opiates, or in pregnant opioid-dependent patients, creates a risk of acute withdrawal syndrome with serious consequences for mother and foetus. Administration must be suspended if opiate analgesics are prescribed. Breast feeding is not recommended during treatment.

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.

Adult dose

Dose: 50 mg (one tablet), after an initial dose of 25 mg (half a tablet)

Route: Oral (tablets should be taken with a liquid)

Frequency: Once daily

Max: A dose of over 150 mg on any single day is not recommended, since this can lead to a higher incidence of side effects

Source: Naltrexone hydrochloride 50 mg film-coated tablets (UK SPC). Treatment must begin with low doses according to the treatment induction schedule: the recommended initial dose is 25 mg (half a tablet) followed by 50 mg per day (one tablet). Treatment should be initiated and supervised by suitably qualified physicians. Naltrexone hydrochloride administered to opioid-dependent persons can cause life-threatening withdrawal symptoms: administration must not be started before a naloxone challenge test is performed and a negative result obtained, and treatment should be considered only in patients who have remained opioid-free for a minimum of 7-10 days; before starting treatment this test must be confirmed by urine screening. The dosage regimen can be modified to improve compliance to a three-times-a-week schedule: 2 tablets (100 mg naltrexone hydrochloride) on Monday and on Wednesday and 3 tablets (150 mg naltrexone hydrochloride) on Friday. A missed dose can be managed by providing 1 tablet per day until the next regular dose administration. Duration: as naltrexone hydrochloride is an adjunctive therapy and the full recovery process in opioid-dependent patients is individually variable, no standard duration of treatment can be stated; an initial period of three months should be considered, though prolonged administration may be necessary. Paediatric population: not recommended in children and adolescents below 18 years old; safe use in children has not been established. Elderly: safe use for the treatment of opiate dependence in the elderly has not been established. Since naltrexone hydrochloride is extensively metabolised by the liver and excreted predominantly in the urine, caution should be observed in patients with impaired hepatic or renal function; liver function tests should be carried out both before and during treatment. Changes in hepatic function tests have been described in obese elderly patients receiving doses higher than recommended (up to 300 mg/day) for the treatment of alcoholism. During treatment, painful conditions should be treated with non-opioid analgesia only.

Dose adjustments

Renal

Contraindicated in severe renal failure. Naltrexone hydrochloride is excreted predominantly in the urine, so caution should be observed in patients with impaired renal function.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to naltrexone hydrochloride or to any of the excipients
Acute hepatitis or liver failure
Severe renal failure
Patients currently dependent on opioids, since an acute withdrawal syndrome may ensue
Any patient with a positive screen for opioids or who has failed the naloxone provocation test
Use in conjunction with an opioid-containing medication; and in combination with methadone

Side effects

Very common: nervousness, anxiety, insomnia; common: irritability, affective disorders; rare: suicidal ideation, attempted suicide
Very common: headache, restlessness; common: dizziness; uncommon: tremor, somnolence
Very common: abdominal pain, nausea and/or vomiting; common: diarrhoea, constipation, decreased appetite
Very common: arthralgia and myalgia, asthenia; very rare: rhabdomyolysis
Common: tachycardia, palpitations, electrocardiogram change, chest pain; uncommon: liver disorder, blood bilirubin increased, hepatitis (transaminases may increase during treatment and decrease to baseline within several weeks after discontinuation)

Interactions

Opioid-containing medicines (cough and cold preparations, antidiarrhoeal preparations, opioid analgesics) — patients may not benefit from them; combination with methadone is contraindicated per the UK SPC
In an emergency requiring opioid analgesia, the amount of opioid required may be greater than usual and the resulting respiratory depression may be deeper and more prolonged
Disulfiram — safety and efficacy of concomitant use unknown; concomitant use of two potentially hepatotoxic medications is not ordinarily recommended unless probable benefits outweigh known risks (US labelling)
Thioridazine — lethargy and somnolence have been reported following doses of naltrexone hydrochloride and thioridazine (US labelling)
Studies to evaluate possible interactions with drugs other than opiates have not been performed; caution is advised with concomitant administration of other drugs (US labelling)

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. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways