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.

Naltrexone has been shown to be the most efficacious amongst the available pharmacotherapies for alcohol use disorder, although more recent research is showing less of a difference.[1] Naltrexone may be more effective in individuals with a genetic susceptibility to alcohol use disorders.

There is some evidence for the use of naltrexone in the treatment of opioid use disorder, but only if the individual is already abstinent from opioid use. Naltrexone will precipitate a severe withdrawal syndrome in patients who are physically dependent on opioids. Any opioids should be discontinued for at least 7 to 10 days prior to initiating treatment.

Naltrexone can cause reversible elevations in transaminases. Bilirubin and liver transaminases should be checked before initiating treatment, and again at 3 months.

  • Start naltrexone at 25 mg per day for 4 days, and then increase to 50 mg per day.
  • There are no clear guidelines around how long to continue prescribing naltrexone. Clinical experience 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 and is no longer has contact with people who misuse opioids.
  • Consider a length of treatment between 3 to 12 months
  • Opioid use including:
    • Anticipated need for opioid analgesics within the next 7 days
    • Current illicit opioid use (as indicated by self-report or a positive urine screen)
    • Buprenorphine-naolxone (Suboxone) or methadone maintenance therapy for the treatment of opioid dependence
    • Currently undergoing opioid withdrawal[2]
  • Safety in liver cirrhosis is not known, and thus naltrexone is contraindicated in acute hepatitis and liver failure. Do not start naltrexone if the patient's bilirubin is elevated or the transaminases are more than 3 times above normal limits.
  • History of sensitivity to naltrexone, to structurally similar compounds (e.g. - naloxone or nalmefene), or to any inactive ingredients in the tablet