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What is naltrexone?

Naltrexone is a prescription drug that is used to treat opioid dependence.

Naltrexone is often referred to as opioid antagonist treatment (OAT). It has no euphoric effect but acts to block the effects of opioids.

Naltrexone is also prescribed for treatment of alcohol dependence, reducing the effects of alcohol on the body, and diminishing craving over time (ADF 2019).

Naltrexone is taken orally as a tablet (usually daily), by subcutaneous implants (a pellet or other container inserted under the skin that slowly releases the drug) or by depot injection (intramuscular injection of naltrexone in a slow release suspension).

Naltrexone treatment is most effective in patients who are highly motivated and who have good social support.

What are the effects?

People in opioid antagonist treatments are less likely to use illicit opioids, or to become involved in the criminal activities associated with illicit drug use.

For those taking naltrexone for alcohol dependence, the drug can reduce the craving for alcohol and reduce the ‘reward’ effects of alcohol use.

The effects of naltrexone may include:

  • Sleep problems
  • Joint and muscle pains
  • Tiredness
  • Abdominal pain and cramps
  • Anxiety
  • Nausea, vomiting
  • Headache

Less common side effects include:

  • Loss of appetite
  • Diarrhoea, constipation
  • Depression and irritability
  • Dizziness
  • Skin rashes

What are the risks?

Toxicity and overdose

Naltrexone blocks the actions of opioids, and rapidly removes a person’s tolerance to opioids so that a given dose of opioids would have more effect than previously. If naltrexone treatment is ceased, individuals may be at risk of opioid overdose if they choose to return to opioid use (Gibson & Degenhardt, 2005).

Dependence and withdrawal

To avoid the risk of initiating acute opioid withdrawal, patients must be opioid free for at least seven to 10 days before starting naltrexone. In some cases, the opioid antagonist drug naloxone is administered to ensure a patient does not experience a severe opioid withdrawal reaction when commencing naltrexone. Caution is recommended when using naltrexone when there are signs of liver damage.

Emergency info

If you, or someone around you, is experiencing undesired or distressing psychological or physical symptoms from the intake of alcohol or other drugs please seek immediate medical attention.

If you need urgent help from ambulance services call Triple Zero (000). If a person has been mixing drugs with alcohol or other drugs, tell the paramedic exactly what has been taken.


For free and confidential advice about alcohol and other drugs, call the National Alcohol and Other Drug hotline on 1800 250 015.

The hotline will automatically direct you to the Alcohol and Drug Information Service in your state or territory.

More resources

The Illicit Drug Reporting System is an Australian monitoring system that identifies emerging trends of local and national interest in illicit drug markets.

The Ecstasy and Related Drugs Reporting System is an Australian monitoring system for ecstasy and related drugs that identifies emerging trends of local and national interest.

The Clinician’s Guide to Illicit Drugs and Health examines the health effects of each of the major illicit drugs.

The Australian Institute of Health and Welfare collects information on alcohol and tobacco consumption, and illicit drug use among the general population in Australia.

The Australian Bureau of Statistics is Australia’s national statistical agency, providing official statistics on a range of economic, social, population and environmental matters of importance to Australia.


Alcohol and Drug Foundation (2019). Naltrexone. Retrieved from: https://adf.org.au/drug-facts/naltrexone/

Gibson, A. and Degenhardt, L. (2005) Mortality related to naltrexone in the treatment of opioid dependence: A comparative analysis, Sydney: National Drug and Alcohol Research Centr