Last published: November 10, 2021

What is naloxone?

Naloxone hydrochloride (brand names Prenoxad, Nyxoid) is a drug that can temporarily reverse opioid overdose. It works by blocking opioid drugs, such as heroin and oxycodone, from attaching to opioid receptors in the brain.

How is it used?

Naloxone can be injected intramuscularly (into a muscle) or delivered by intranasal spray. It may be administered by medical professionals, such as paramedics, as well as family, friends, or bystanders in an emergency where someone is experiencing an overdose.

Best practice is to provide a person who might be administering naloxone with training. See the bottom of this page for information on where to find training providers

Effects of naloxone

The effects of naloxone are to temporarily block opioid receptors and prevent opioid drugs from working. Naloxone cannot be used to get high, so it has no potential for non-prescribed use.

There is no evidence that extended use of naloxone can cause harmful physical effects or dependence. People who take naloxone do not develop a tolerance to its effects and there have been no reported deaths from naloxone overdose.1, 2

Side effects

Most side effects from naloxone are mild. However, if someone is opioid-dependent and they are given a high dose of naloxone, it can bring on symptoms of opioid withdrawal2 such as:

  • nausea and vomiting
  • sweating
  • trembling
  • nervousness
  • fast pulse.2

In rare cases, even a person who is not opioid-dependent might experience:

  • an allergic reaction with symptoms such as swelling of the face, lips, tongue and throat, wheezy breathing, chest tightness, intense rash with itching
  • high blood pressure
  • irregular heartbeat
  • seizures.2

Naloxone and opioid overdose

People who have been revived with naloxone after overdosing on opioids may experience a strong urge to take more opioid drugs, especially if they are dependent.

Taking opioid drugs after naloxone is very dangerous. Naloxone only stays in the body for a short period of time (1 to 1.5 hours) whereas heroin and other opioid drugs stay in the body for much longer. The effects of sustained-release opioids like OxyContin® and MS Contin® can last for over 12 hours, so naloxone will wear off long before the opioid has left the system. This means that taking more opioids after taking naloxone could cause a second overdose.3

For information about naloxone training and accessibility in your state or territory, get in touch with peak harm minimisation bodies or check the Pennington Institute to find out what local service providers are delivering training.


Western Australia

New South Wales


Northern Territory

Australian Capital Territory

  1. Petty J, McNally S, Ryan J. Saving lives: Australian naloxone access model. Melbourne: Penington Insitute; 2018.
  2. Upfal J. Australian Drug Guide. 8th edition ed. Victoria: Griffin Press; 2016.
  3. Penington Institute. Overdose Basics Melbourne: Penington Institute; 2020 [cited 2020 March 12, ].

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allergic reaction, high blood pressure, intense rash, irregular heart beat, nausea, reverse opioid overdose, seizures, vomiting