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.
Quick facts
- Group
- 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.
Mechanism of action
The figure shows naloxone, a closely related antagonist, in the inactive mouse μ receptor; nalmefene occupies the same site.
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 →
- 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
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
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.
Connections
← Back to the class: 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 (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.