Naltrexone — opioid receptor antagonist for alcohol and opioid dependence

Mechanism and formulations

Pharmacologically, naltrexone competitively inhibits opioid receptors. It is available as an oral tablet taken daily and as an extended-release intramuscular injection given about once monthly; the depot injection can improve adherence where daily pills are difficult to maintain. Its antagonist action contrasts with agonist therapies that stimulate opioid receptors.

Clinical indications and use

Naltrexone is used as part of a comprehensive treatment plan that includes counseling, psychosocial support and monitoring. In alcohol use disorder it can decrease craving and reduce the frequency of heavy drinking. For opioid dependence it is appropriate only after complete opioid detoxification because administration to an opioid-dependent person can precipitate acute withdrawal.

Safety, precautions and monitoring

Before initiation clinicians ensure the patient is opioid-free for a suitable interval to avoid precipitated withdrawal. Liver function tests are recommended at baseline and periodically in people with hepatic risk factors because high doses have been associated with hepatotoxicity. Common adverse effects include nausea, headache, fatigue and sleep disturbance.

Emergency distinction and interactions

Naltrexone is not a treatment for acute opioid overdose. In emergency overdose situations, the short-acting opioid antagonist naloxone is the preferred agent for rapid reversal; see guidance on overdose management. Naltrexone blocks the effects of prescribed or illicit opioids and will interfere with opioid analgesia, so pain management plans should be adjusted accordingly.

Comparisons and patient considerations

Unlike methadone or buprenorphine—opioid agonist or partial-agonist maintenance therapies—naltrexone produces no opioid stimulation and has no potential for opioid diversion. That profile suits patients who desire a non‑opioid option or cannot take agonist therapy, but some patients prefer agonist maintenance because it eases withdrawal and cravings during early recovery.

Key points

• Action: opioid receptor antagonist that reduces alcohol craving and blocks opioid effects.
• Formulations: daily oral tablet and monthly extended-release injection.
• Use: alcohol use disorder and relapse prevention after opioid detoxification.
• Precautions: ensure opioid abstinence before start, monitor liver function, not for emergency overdose (use naloxone).