naloxone
Meaning of naloxone: One of the few drugs that does nothing at all unless a particular poison is present, which is what makes it usable by bystanders.
Definition of naloxone
Naloxone is an opioid antagonist: it binds opioid receptors without switching them on, and it binds tightly enough to displace opioid drugs already attached to them. Given during an overdose it restores breathing within minutes. It is supplied as an injection and as a nasal spray, and it has no effect at all in someone who has not taken an opioid.
How does it reverse an overdose?
What makes an overdose lethal is not sleepiness but the loss of the drive to breathe: opioids blunt the brainstem's response to rising carbon dioxide, so breathing slows, becomes shallow and eventually stops. Naloxone holds the mu opioid receptor more tightly than most opioids do, so it evicts them and then sits there doing nothing. Breathing typically returns within minutes. Because it reverses everything at once, it also removes pain relief, and in someone physically dependent it triggers abrupt withdrawal: sweating, vomiting, aching, agitation and a racing pulse. That reaction is thoroughly unpleasant, but it is not dangerous in the way respiratory arrest is.
Why can the effect fade first?
Naloxone leaves the body faster than many of the drugs it is used against. Long-acting opioid medicines such as methadone, slow-release formulations, and large amounts still being absorbed from the stomach can all outlast it, so sedation and slowed breathing may return once it clears. Very potent synthetic opioids may take more than one dose to displace. This is why observation continues after an initial reversal rather than ending with it, and why repeat dosing or a continuous infusion is sometimes required.
Where else is it used?
| Use | How it works there |
|---|---|
| Emergency reversal | Injection or nasal spray, including by bystanders under take-home distribution programs |
| After anesthesia or procedural sedation | Small measured doses to lift excessive sedation without abolishing pain relief entirely |
| Combined with oxycodone in one tablet | Acts locally in the gut to counter constipation, then is destroyed by the liver before reaching the brain |
| Combined with buprenorphine | Has little effect taken as directed, but deters injection of the tablet or film |
Those last two exploit the same fact: taken by mouth, naloxone is almost entirely broken down on its first pass through the liver, so as an antagonist it reaches the gut but not the brain. Injected, it reaches both, which is precisely what makes the combination products resistant to misuse.
Also known as
Used in a sentence
Naloxone was administered to reverse the effects of the suspected opioid overdose.
Good to know
Naloxone's effect can wear off before that of a longer-acting opioid, which is why continued observation and repeat dosing may be needed after an initial reversal of overdose symptoms.