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Naltrexone facts

What is naltrexone?

Is naltrexone right for you?

What does the treatment involve?

What are the side effects?

How can I support someone who is on naltrexone?

What is naltrexone?

Please note: The information given on this page is not medical advice and should not be relied upon in this way. It is correct at the time of publication. People wanting medical advice on this issue should consult a health professional.

Naltrexone is a prescribed drug, which may be used:

  • to help people who have withdrawn (detoxified) from opioids such as heroin, to stay off those drugs.
  • to help people with alcohol dependence, not to drink alcohol.
  • as an experimental treatment during rapid withdrawal from opioids.


This page explains the use of naltrexone to assist people in staying off heroin after withdrawal.

How does it work?

Naltrexone is classed as an opioid antagonist. It works by blocking the opioid receptors in the brain and therefore blocking the effects of heroin and other opioids.

It can assist in keeping people off heroin because they will be aware that they cannot achieve a 'high' from using heroin. It does not directly stop a person wanting to use heroin, although it may reduce or prevent cravings in some people.

You cannot become physically dependent on naltrexone and it does not produce any euphoric effects.

How effective is it?

There have been a lot of media reports on naltrexone, often describing it as a 'miracle cure' for heroin. However, most drug professionals agree that the success of naltrexone treatment depends on:

  • the person's particular situation, including their level of commitment to staying off heroin and the level of support available to them.
  • it being one part of a comprehensive treatment program, which includes regular counselling. 

In fact, recent studies have suggested that many clients do not remain on naltrexone and will often return to heroin use. More studies are being conducted that may provide a clearer picture of naltrexone’s effectiveness. It is important to note that naltrexone treatment may be effective for some people, but will not suit everyone.

Is naltrexone right for you?

Naltrexone is one of a number of treatments for heroin dependence. Other treatments include:

  • methadone maintenance
  • withdrawal/detoxification (residential or home-based/medical or non-medical) 
  • counselling (outpatient or as part of residential rehabilitation).


For best results, a person wanting to stay off heroin is advised to take part in a treatment program that deals with both the physical and psychological aspects of drug dependency. This may mean combining naltrexone treatment with counselling, or progressing from withdrawal to counselling or rehabilitation.

A doctor or drug counsellor that spends time assessing the person's situation and explaining the different treatment options will recommend a program that is appropriate for that person.

If applying for the naltrexone program, see a doctor who is experienced in this treatment. The alcohol and other drug information service in your state or territory can provide an appropriate referral.

To be eligible for naltrexone treatment, an individual must:

  • be free of heroin and other opioids for 7–10 days, or 10 days for methadone, before commencing naltrexone maintenance treatment, otherwise there is a risk that the individual may experience acute, instant withdrawal.
  • be free from 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.

People who are highly motivated to be opioid free, and have support from family and friends, are more likely to benefit from the treatment.

Other considerations 

To have the best chance of giving up, and staying off heroin, it is important that the person involved should:

  • have support. Practical and emotional support from family, friends, doctor and/or drug counsellor is very important to help the person through the process of withdrawal.
  • be away from drugs. To be out of the environment in which drugs are readily available (this may mean giving up old friends, moving to a different area).
  • understand his or her drug use. To understand why the person uses a particular drug, what might trigger them to using, what other emotional and practical issues they might be facing (a drug counsellor can help the person through this).

What does the treatment involve?

Treatment involves taking a prescribed dose of naltrexone for as long as the prescriber believes it is needed—the length of the program depends on the individual's situation.

Naltrexone is taken as a tablet. The usual dose is 50mg each day, although sometimes a higher dose is prescribed, and taken less often (e.g. 100mg every second day, or 150mg every 3 days).

Often a carer, family member, doctor or pharmacist supervises the administration of the dose.

The Naloxone (Narcan) Challenge Test (NCT) 

After the person has managed to stay off opioids for a period of 7–10 days, and has had a negative urine test for opioids, the doctor will often give a naloxone (Narcan) challenge test. This helps to determine the level of physical dependence on opioids.

This involves an injection of naloxone, followed by 20 minutes of monitoring for signs of withdrawal. If moderate to severe signs of withdrawal are identified, the test can be repeated 24 hours later. If the withdrawal symptoms are only mild, the first dose of naltrexone can be given.

Agitation, temporary numbness and pins and needles have been infrequently reported with the use of naloxone.

What are the side effects?

Naltrexone is generally well tolerated, however some side effects have been reported. Most of these symptoms occur very early in treatment—usually during the first week or so. Some of these effects may be caused by the combined experience of withdrawal from opioids and taking naltrexone.

The most common side effects include: difficulty sleeping, anxiety, abdominal pain or cramps, nausea, vomiting, low energy, joint and muscle pain and headache.

Less common side effects include: loss of appetite, diarrhoea, constipation, increased thirst, increased energy, feeling depressed or irritable, dizziness, skin rash, delayed ejaculation, decreased potency, and chills.

Warning: When taken in large doses naltrexone may cause liver damage. When taken in recommended doses it is unlikely that naltrexone will cause liver damage. If you experience excessive tiredness, unusual bleeding or bruising, loss of appetite, pain in the upper right part of your abdomen that lasts more than a few days, light-colored bowel movements, dark urine, or yellowing of the skin or eyes, seek medical assistance immediately.

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

Naltrexone and painkillers

While an individual is taking naltrexone, some strong painkillers will not work for them. This is because many strong painkillers are opioid drugs, and naltrexone works by blocking the effects of opioids.

If, for some reason, the person needs strong painkillers, it is important that medical staff are aware that they are taking naltrexone. They will then be able to prescribe a different kind of drug for pain relief.

An emergency wallet card is a good way of alerting medical staff that a patient is taking naltrexone.

Risk of overdose

While a person is on naltrexone, they will have lower tolerance to heroin. This means that there is a serious risk of overdose when heroin is used, either after a naltrexone dose has been skipped or if a person stops taking naltrexone altogether.

People who are planning to use heroin after being on naltrexone should consider themselves 'new' users. Overdose may occur if the person uses the same or even a smaller amount of heroin than they were used to taking before being on naltrexone.

Always call triple zero (000) if a drug overdose is known or suspected—and remember that paramedics are not obliged to involve the police.

Find out more about overdose.

How can I support someone who is on the naltrexone program?

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

If you take on the role of support person, you will both need to agree on what this will, and will not, involve. This might include whether you will inform the doctor if problems arise, and what kinds of support you are willing and able to give.

Some of the types of support you might offer, could include:

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


This is a challenging role, so remember to take care of yourself, and arrange your own support networks.

Read more about support for family members 

Read more about treatment.

Last updated: 24 January 2013

Information you heard is intended as a general guide only. This audio is copyrighted by the Australian Drug Foundation. Visit www.DrugInfo.ADF.org.au for more