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It is an opioid antagonist. It completely blocks the subjective effects of opioids by competitively binding at opioid receptors. Duration of action is dose related and much longer than that of naloxone.


Opioid dependence (as an aid to prevent relapse). Adjunctive treatment in chronic alcoholism.


Opioid dependence: Patients should be opioid free for atleast 7-10 days. Initiate therapy in specialist clinics only. 25 mg initially, then 50 mg daily; once stabilized, total weekly dose may be divided and given on 3 alternate days of the week. Adjunctive treatment in chronic alcoholism: 50 mg once daily.


Patients concurrently dependent on opioids; acute hepatitis or hepatic failure, acute opioid withdrawal; patients on therapeutic opioid analgesics; hypersensitivity.

Special Precautions

Hepatic or renal impairment; LFTs needed before and during treatment. Test for presence of opioid molecules in the body using urine screening or naloxone challenge, if required (patients should be opioid free for atleast 7-10 days prior to initiating naltrexone therapy). Patients are strictly warned against the use of opioids while on naltrexone. Pregnancy and lactation.

Side Effects

Abdominal pain, nausea, vomiting, anxiety, insomnia, lethargy, headache, musculoskeletal pain, anorexia, diarrhea, constipation, increased thirst, sweating and lachrymation, chest pain, irritability, chills, dizziness, sexual dysfunction, rash, liver function abnormalities and reversible idiopathic thrombocytopenia.

Drug Interactions

Excessive opioids can result in acute opioid intoxication; in addition, excessive opiates release histamine resulting in facial swelling, itching and erythema. Concurrent hepatotoxic drugs may increase the risk of hepatic dysfunction.

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