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Naltrexone for opioid addiction

How naltrexone works

Naltrexone is a competitive opioid antagonist, similar to naloxone. It blocks the action of opioids and thus may help to prevent relapse in some patients.

Although some recent trials have shown short-term benefit, the long-term effectiveness of naltrexone is uncertain (Comer et al., 2006; Kirchmayer et al., 2002).

Prescribing naltrexone

Naltrexone will precipitate a severe withdrawal syndrome in patients who are physically dependent on opioids, so opioids should be discontinued for seven to 10 days prior to initiating treatment.

Naltrexone can cause reversible elevations in transaminases, particularly at high doses. Safety in cirrhosis is not known, and naltrexone is contraindicated in acute hepatitis and liver failure. Therefore, check bilirubin and liver transaminases before initiating treatment, and again at three months. Do not start naltrexone if the patient's bilirubin is elevated or the transaminases are more than three times the normal level.

Start naltrexone at 25 mg per day for four days, and then increase to 50 mg per day.

There are no clear guidelines around how long to continue prescribing naltrexone. Clinical experience with disulfiram and alcohol suggests continuing the medication until the patient:

  • no longer has cravings
  • is confident that relapse will not happen if the medication is stopped
  • has strong supports in place
  • no longer has contact with people who misuse opioids.