[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) › Naloxone

[Pharmacology](https://durgical.com/en/pharmacology/) · [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)

# Naloxone

An opioid antagonist: it pushes opioids off their receptor and reverses an overdose within minutes. It does almost nothing when no opioid is present.

Updated 2026-11-01

- Class: [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)
- Receptor: μ-opioid receptor
- ATC code: V03AB15
- WHO Model List of Essential Medicines

◎**μ-opioid receptor**Naloxone

ⓘ The figure shows naloxone in the inactive mouse μ receptor; the structure also holds a nanobody and an allosteric modulator, which are hidden.

**Target in 3D:** μ-opioid receptor. PDB structure 9BJK (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/9BJK) · Drag to rotate · pinch to zoom

## Mechanism of action

Naloxone is a pure competitive antagonist at opioid receptors, with the highest affinity for the μ receptor. It takes the agonist's site, displaces it and holds the receptor in its inactive shape without activating the G protein. It thus reverses respiratory depression, sedation and miosis within minutes; in a dependent person it can trigger acute withdrawal.

- Competes with the opioid for the μ receptor and displaces it
- The receptor stays inactive: the Gi protein is not switched on
- The breathing center regains its drive within minutes
- It wears off sooner than many opioids: sedation can return

## Pharmacokinetics

**Absorption**
Given intravenously, intramuscularly, subcutaneously or intranasally.

**Metabolism**
Liver, by glucuronidation (mainly naloxone-3-glucuronide).

**Elimination**
Kidney, as metabolites.

**Half-life**
About one and a half hours.

**Onset and duration**
Within about two minutes intravenously; a little longer intramuscularly or subcutaneously.

## Indications

- Opioid overdose (coma, respiratory depression and miosis), including fentanyl
- Reversal of opioid-induced respiratory depression after anesthesia
- Combined with sublingual buprenorphine to deter injection

## Adverse effects

### Common

- Withdrawal symptoms in dependent people: agitation, sweating, vomiting, pain
- Tachycardia and hypertension

### Serious (rare, important)

- Severe acute withdrawal
- Return of respiratory depression as its effect wears off

## Contraindications

- Known hypersensitivity to naloxone

## Key interactions

**Opioid agonists (morphine, fentanyl)**
Reverses their effect; in dependent people it precipitates withdrawal.

**Buprenorphine**
Its high affinity makes reversal harder and may need more naloxone.

**Long-acting opioids (methadone)**
They outlast naloxone: respiratory depression can return.

## What is monitored

- Respiratory rate and level of consciousness for several hours after waking
- Signs of withdrawal

## Memory aid

Naloxone is a bouncer who throws the opioid out of the club but ends the shift early: if the opioid is still waiting outside, it walks back in.

## Test yourself

Think of the answer, then tap the question to see it.

## What kind of ligand is naloxone at the μ receptor?

A pure competitive antagonist: it takes the agonist's site without activating the receptor and displaces the agonist.

## Why does naloxone not work for a benzodiazepine overdose alone?

It acts only on opioid receptors; benzodiazepines act on the GABA-A receptor. Naloxone does almost nothing when no opioid is present.

## Why is buprenorphine combined with naloxone in sublingual tablets?

Taken sublingually, naloxone is barely absorbed and does not interfere; if someone dissolves and injects the tablet, naloxone acts and precipitates withdrawal.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/naloxone/)

## Related drugs

- [Morphine](https://durgical.com/en/pharmacology/morphine/)
- [Fentanyl](https://durgical.com/en/pharmacology/fentanyl/)

[← Back to the class: Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Naloxone Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a612022.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Opioid overdose](https://www.who.int/news-room/fact-sheets/detail/opioid-overdose) (World Health Organization, 2025); [NALOXONE HYDROCHLORIDE INJECTION, USP, AUTO-INJECTOR- naloxone hydrochloride injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=b5463553-b775-47a3-8d10-31e01ca1ec72) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=V03AB15) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/naloxone/
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