Naltrexone pills

Last published: October 07, 2020

What is naltrexone?

Naltrexone is a prescription drug. It belongs to a group of drugs known as opioid antagonists. These block the effects of heroin and other opioid drugs. Naltrexone is used in pharmacotherapy, in which a drug of dependence is replaced with a prescribed drug. Pharmacotherapy helps to stabilise people’s lives and reduce the harms related to drug use.1

Naltrexone may be used:

  • to help people who have withdrawn (detoxified) from opioids such as heroin to stay off those drugs through the awareness that the effects of naltrexone will stop them achieving a ‘high’
  • as an experimental treatment during rapid withdrawal from opioids.

Naltrexone can also be prescribed to people with alcohol dependence.

How is it used?

Naltrexone is taken as a tablet. The length of the course will depend on each person’s needs and situation.

It can also be administered via an implant. Treatment with naltrexone implants is permitted in Australia under the requirements of the TGA Special access scheme.

To be eligible for the treatment for opioid dependence, a person must:

  • be free of heroin and other opioids for 7–10 days (or 10 days for methadone) before starting naltrexone maintenance treatment; otherwise they may experience acute, instant withdrawal. People who intend to start naltrexone maintenance treatment can expect to be tested in order to confirm that they are clear of opioid drugs. An example of such a test is the Naloxone Challenge Test (NCT), in which the opioid antagonist drug naloxone is administered to determine a person’s current level of physical dependence on opioids.3
  • have no existing liver conditions, such as acute hepatitis.
  • seek advice if they are pregnant or breastfeeding as naltrexone may not be safe for use during pregnancy.2

Alcohol and naltrexone

Naltrexone can be prescribed to people with alcohol dependence. Its use in that context works in several ways, it can:

  • reduce the craving for alcohol
  • reduce the quantity of alcohol consumed1
  • reduce the ‘reward’ effects of alcohol use
  • help people remain abstinent from alcohol
  • reduce the tendency to want to drink more if a person consumes alcohol.

If a person consumes alcohol while using naltrexone, they will still experience the effects of alcohol, so their judgement, coordination and ability to perform tasks such as driving and operating machinery will still be affected.

Regular blood tests to monitor liver function both before and during naltrexone treatment are recommended.6

How effective is it?

Naltrexone may not work for everyone, so it is important to consult a doctor or drug counsellor to find the best approach.

Naltrexone treatment is more likely to be successful if it is part of a comprehensive treatment program that includes counselling, alternative therapies and the development of a positive network of peers, friends and a support group.

Some studies suggest that many clients don’t remain on naltrexone and return to heroin use. Future studies may provide a clearer picture of the drug’s effectiveness.

In terms of its use to treat alcohol dependence, naltrexone may be more effective for preventing relapse to heavy drinking and reducing high levels of alcohol consumption than for maintaining abstinence from alcohol.6

Effects of naltrexone

There is no safe level of drug use. Use of any drug always carries some risk – even medications can produce unwanted side effects. It’s important to be careful when taking any type of drug.

Naltrexone affects everyone differently, based on:

  • the amount taken
  • size, weight and health of the person taking it
  • whether the person is used to taking it
  • whether other drugs are taken around the same time.

Side effects

Naltrexone has few side effects, and these usually go away after the medication is taken for a few days.

The reported side effects include:

  • sleep problems
  • tiredness
  • anxiety
  • headache
  • joint and muscle pains
  • abdominal pain and cramps
  • nausea
  • vomiting.2

Less common side effects include:

  • feeling energetic
  • loss of appetite
  • thirst
  • diarrhoea, constipation
  • depression and irritability
  • dizziness
  • skin rashes
  • decreased potency, delayed ejaculation
  • chills.4

Naltrexone may affect mental alertness and/or coordination. If affected, do not drive a motor vehicle or operate machinery.

Dose-related effects

Large doses of naltrexone may cause liver damage. Seek medical advice immediately if these symptoms are experienced:

  • excessive tiredness
  • unusual bruising or bleeding
  • loss of appetite
  • pain in the upper right area of the abdomen that lasts more than a few days
  • light-coloured bowel movements
  • dark urine
  • yellowing of skin or whites of the eyes.4

Risk of heroin overdose

Naltrexone will lower a person’s tolerance to heroin. This means that there is a serious risk of overdose if they use heroin after a missed dose of naltrexone or after treatment has finished.3

People who plan to use heroin after being on naltrexone should consider themselves ‘new’ users.

If you believe someone has overdosed on heroin, call an ambulance straight away by dialling triple zero (000). Ambulance officers don’t need to involve the police.3

Using naltrexone with other drugs

The effects of taking naltrexone with other drugs – including over-the-counter or prescribed medications – can be unpredictable and dangerous. In particular:

Naltrexone + opioid painkillers: the naltrexone will stop opioid painkillers from working.3

In cases where a person on opioid painkillers is likely to be given naltrexone (or vice versa), medical staff will need to be informed so that a different kind of painkiller can be prescribed. Medic alert bracelets are available for purchase online.

Supporting someone who is on a naltrexone program

People who are taking naltrexone will need both emotional and practical support.

Those who are to give support should decide, in collaboration with the person undergoing treatment, exactly what the support will entail. This might include whether they will inform a doctor if problems arise.

It could also include:

  • being committed to supervising the naltrexone dose for the duration of the treatment
  • knowing what to do in the event of an overdose
  • going with friends/family members to appointments (such as those with doctors, counsellors)
  • encouraging the person to develop their friendship and support networks and to get involved in positive, healthy activities (such as taking a class, joining a support group, being active)
  • attending couples or family counselling if appropriate.5

This is a challenging role, so people offering support will need to take care of themselves and arrange their own support networks.


People can stop taking naltrexone at any time. They will not experience withdrawal symptoms.

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  1. Miranda, R, Padovano, H, Gray, J, Wemm, S & Blanchard, A, 2018, ‘Real-Time assessment of alcohol craving and naltrexone treatment responsiveness in a randomized clinical trial’ Addictive Behaviours, Vol 83, Pp 72-78
  2. Brands, B., Sproule, B., & Marshman, J. (Eds.) (1998). Drugs & drug abuse. (3rd Ed.). Ontario: Addiction Research Foundation.
  3. Substance Abuse and Mental Health Services Administration. (2009). The facts about naltrexone for treatment of opioid addiction.
  4. Galanter, M. & Kleber, H. (Eds.). (2008). Textbook of substance abuse treatment. (4th ed.). Washington, DC: American Psychiatric Publishing, Inc.
  5. HealthDirect. (n.d.). Brand name: Revia
  6. Family Drug Support. (2007). Other pharmacotherapies.
  7. Haber, P., Lintzeris, N., Proude, E., & Lopatko, O. (2009). Guidelines for the treatment of alcohol problems, Australian Government Department of Health and Ageing.


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