[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/) › Nalmefene

# Nalmefene

## Opioids and antagonists?

Opioids and antagonists

An injectable opioid antagonist that reverses opioid overdose and lasts longer than naloxone. It can trigger sudden withdrawal in dependent patients.

Updated Nov 1, 2026

## Quick facts

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

**Target**
μ-opioid receptor (antagonist)

**Used for**
Known or suspected opioid overdose

**Key effects**
Nausea and vomiting · Fever and dizziness

**Monitor**
Breathing · Signs of withdrawal

**ATC**
N07BB05

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◎**μ-opioid receptor (antagonist)**Nalmefene

ⓘ The figure shows naloxone, a closely related antagonist, in the inactive mouse μ receptor; nalmefene occupies the same site.

**Target in 3D:** μ-opioid receptor (antagonist). 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

Nalmefene is an opioid antagonist with no agonist activity. It displaces opioids from their receptors and so reverses respiratory depression, sedation and low blood pressure. It acts longer than naloxone.

- Binds opioid receptors without activating them
- Displaces the opioid from the μ receptor
- Breathing and consciousness return

## Indications

- Known or suspected opioid overdose [Opioid overdose →](https://durgical.com/en/conditions/opioid-overdose/)
- Reversal of opioid effects, including respiratory depression, after anaesthesia

## Adverse effects

### Common

- Nausea and vomiting
- Fast heart rate and high blood pressure
- Fever and dizziness

### Serious (rare, important)

- Acute opioid withdrawal in dependent patients
- Pulmonary oedema, blood-pressure swings and arrhythmias after abrupt postoperative reversal
- Return of respiratory depression when a long-acting opioid outlasts it

## Contraindications

- Known hypersensitivity to nalmefene

## Key interactions

**Opioid agonists**
Reversal of their effects and possible withdrawal

**Buprenorphine**
Reversal may be incomplete

## What is monitored

- Breathing, consciousness and oxygen saturation until the risk of recurrence is low
- Signs of withdrawal, heart rate and blood pressure

## Administration and safety

- Given intravenously; intramuscular or subcutaneous if there is no venous access
- Does not replace airway management, ventilation and oxygen
- Look-alike names: nalmefene, naloxone and naltrexone are different products

## Pregnancy and breastfeeding

Human data are lacking; it is used when clearly needed, as in an overdose.

## Nursing care

- Support the airway and ventilation first
- Observe the patient for a prolonged period, above all after methadone or other long-acting opioids
- Expect and manage withdrawal: agitation, vomiting, sweating, fast pulse

## Pharmacokinetics

**Metabolism**
Mainly glucuronidation in the liver to an inactive product

**Half-life**
About 11 hours, longer than naloxone

## Memory aid

Nalmefene: «naloxone with a longer fuse» – same reversal, longer action, same withdrawal risk.

## Test yourself

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

## How does nalmefene differ from naloxone?

It acts longer.

## Why is a patient still observed after a good response?

Respiratory depression can return if the opioid outlasts the antagonist.

## Which opioid may be only partly reversed?

Buprenorphine.

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

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 4

- [Naloxone](https://durgical.com/en/pharmacology/naloxone/)
- [Naltrexone](https://durgical.com/en/pharmacology/naltrexone/)
- [Buprenorphine](https://durgical.com/en/pharmacology/buprenorphine/)
- [Fentanyl](https://durgical.com/en/pharmacology/fentanyl/)

## Related conditions 1

- [Opioid overdose](https://durgical.com/en/conditions/opioid-overdose/)

[← 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: [DailyMed - NALMEFENE HYDROCHLORIDE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3abfbffc-9e52-4fc6-ae92-6e0a97f4afe7) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N07BB05) (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/nalmefene/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/nalmefene/