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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Other
Nalmefene is a long-acting opioid antagonist used for the emergency treatment of known or suspected opioid overdose and, in some regions, for the reduction of alcohol consumption in adults with alcohol dependence.
Name
Nalmefene
Raw Name
NALMEFENE HYDROCHLORIDE
Category
Other
Salt Form
Hydrochloride
Drug Count
4
Variant Count
5
Last Verified
February 17, 2026
RxCUI
2592953, 2672926, 2639721, 2639727, 2720806, 2720812
UNII
K7K69QC05X
About Nalmefene
Nalmefene is a long-acting opioid antagonist used for the emergency treatment of known or suspected opioid overdose and, in some regions, for the reduction of alcohol consumption in adults with alcohol dependence.
Detailed information about Nalmefene
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Nalmefene.
Historically, nalmefene was first approved by the U.S. Food and Drug Administration (FDA) in 1995 as an injectable formulation (Revex) for the management of opioid overdose and the reversal of post-operative opioid effects. While the injectable form was discontinued in the U.S. market for commercial reasons in the mid-2000s, the drug saw a resurgence in clinical interest due to the escalating opioid crisis. In May 2023, the FDA approved a high-dose nasal spray formulation (brand name OPVEE) for the emergency treatment of known or suspected opioid overdose in adults and pediatric patients aged 12 years and older. Outside the United States, specifically in the European Union, nalmefene is approved under the brand name Selincro for the reduction of alcohol consumption in adult patients with alcohol dependence who have a high level of drinking risk.
To understand how nalmefene works, one must first understand the opioid system. The human body has several types of opioid receptors: Mu (μ), Delta (δ), and Kappa (κ). Most opioids of abuse, such as heroin or fentanyl, primarily target the Mu receptor, leading to pain relief, euphoria, and, in high doses, life-threatening respiratory depression (dangerously slow breathing).
Nalmefene acts as a competitive antagonist at the Mu and Delta receptors. This means it has a high affinity (strong attraction) for these receptors and 'bumps' opioid molecules off the receptor sites, or prevents them from binding in the first place. By occupying the Mu receptor without activating it, nalmefene rapidly reverses the respiratory depression caused by opioids.
What sets nalmefene apart from its cousin, naloxone, is its activity at the Kappa receptor. Nalmefene acts as a partial agonist at the Kappa receptor. Some researchers believe this unique profile helps modulate the reward system, which is why it is utilized in the treatment of alcohol use disorder. By blocking the 'high' associated with alcohol-induced opioid release and modulating the Kappa system, it helps patients reduce their desire to consume alcohol.
Understanding the pharmacokinetics (how the body processes the drug) of nalmefene is crucial for clinical management, especially in overdose scenarios where the duration of action is critical.
Nalmefene is utilized for several distinct clinical indications, depending on the formulation and the regulatory jurisdiction:
Nalmefene is currently available in the following formats:
> Important: Only your healthcare provider can determine if Nalmefene is right for your specific condition. In an emergency overdose situation, call emergency services immediately after administering the first dose.
Dosage for nalmefene depends entirely on the indication and the formulation being used.
For the emergency treatment of a suspected opioid overdose, the standard dose is one spray (2.7 mg) administered into one nostril. Because synthetic opioids like fentanyl are extremely potent, a single dose may not always be sufficient. If the patient does not respond or if respiratory depression recurs, additional doses may be administered every 2 to 5 minutes in alternating nostrils until emergency medical assistance arrives.
In jurisdictions where the oral form is approved, the typical dose is 18 mg taken orally once daily, preferably 1 to 2 hours before the time the patient anticipates a risk of drinking. Unlike many other medications, it is often used 'as needed'—if the patient starts drinking without having taken the medication, they should take one tablet as soon as possible.
Nalmefene is primarily excreted as metabolites in the urine. While no specific dose adjustment is required for the emergency nasal spray (as it is a life-saving intervention), chronic use of oral nalmefene is generally not recommended in patients with severe renal impairment (estimated glomerular filtration rate < 30 mL/min/1.73m²).
Because nalmefene is extensively metabolized by the liver, its clearance is reduced in patients with liver disease. For the emergency nasal spray, the benefit of reversing an overdose outweighs the risk of liver-related side effects. However, for the treatment of alcohol dependence, nalmefene is contraindicated in patients with severe hepatic impairment (Child-Pugh Class C).
Clinical studies have not identified significant differences in safety or efficacy between elderly patients and younger patients. However, because older adults are more likely to have decreased renal or hepatic function, healthcare providers may monitor these patients more closely during chronic treatment.
If prescribed for alcohol dependence, the tablet should be swallowed whole. It can be taken with or without food. Do not crush, chew, or split the tablet, as this may affect the absorption rate.
For the treatment of alcohol dependence, if a patient misses a dose and intends to drink, they should take the dose as soon as they remember. If they have already started drinking, they should still take the dose. Do not double the dose to make up for a missed one.
While nalmefene is used to treat opioid overdoses, an overdose of nalmefene itself is rare but possible. Symptoms of nalmefene overdose may include extreme nausea, dizziness, confusion, and symptoms of precipitated opioid withdrawal (if opioids are present in the system). In case of a suspected overdose of nalmefene, contact a Poison Control Center or seek emergency medical care immediately.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.
Side effects of nalmefene can vary significantly depending on whether the patient has opioids in their system. In healthy volunteers or those using it for alcohol dependence, the most common side effects include:
> Warning: Stop taking Nalmefene and call your doctor immediately if you experience any of these.
When used chronically for alcohol dependence, long-term side effects are generally mild. However, some patients may experience persistent sleep disturbances or mild changes in mood. Unlike naltrexone, nalmefene has not shown a significant pattern of dose-related hepatotoxicity (liver damage) in clinical trials, but liver function should still be monitored in patients with pre-existing liver disease.
No FDA black box warnings currently exist for Nalmefene. However, the FDA-approved labeling for OPVEE (nalmefene nasal spray) contains strong warnings regarding the risk of precipitated opioid withdrawal and the necessity of emergency medical follow-up after use.
Report any unusual symptoms to your healthcare provider. If you are using nalmefene for alcohol dependence and experience thoughts of self-harm or deep depression, contact a mental health professional immediately.
Nalmefene is a high-potency medication that must be used with caution, particularly in emergency settings. The most critical safety point is that nalmefene is not a substitute for emergency medical care. Even if a patient wakes up and appears normal after receiving nalmefene for an overdose, they must still be evaluated by medical professionals. The opioids they took may last longer than the nalmefene, or they may experience complications like pulmonary edema or aspiration pneumonia.
No FDA black box warnings for Nalmefene.
Nalmefene can cause dizziness, somnolence (sleepiness), and tremors. Patients starting oral nalmefene should not drive or operate heavy machinery until they are certain the medication does not impair their coordination or judgment. In the context of an overdose reversal, the patient should never drive themselves after the event.
When used for alcohol dependence, nalmefene is intended to be taken while the patient is still drinking (to reduce consumption). However, it does not prevent the intoxicating effects of alcohol or the impairment of motor skills. Combining nalmefene with heavy alcohol use does not increase the risk of liver damage more than alcohol alone, but it also does not 'cure' the effects of intoxication.
There is no evidence of a physical withdrawal syndrome from nalmefene itself. However, if a patient stops taking nalmefene while still struggling with opioid or alcohol use disorder, they will lose the protective effects of the medication, increasing the risk of relapse or overdose.
> Important: Discuss all your medical conditions with your healthcare provider before starting Nalmefene.
Nalmefene may interfere with certain urine drug screens that use immunoassays for opioids. Depending on the specific test, it may produce a false-positive result for certain opioids. If a drug test is required, inform the laboratory that you are taking nalmefene so that confirmatory testing (like GC-MS or LC-MS) can be performed.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking. For each major interaction, the mechanism usually involves competitive receptor binding or metabolic pathway interference, which can lead to reduced efficacy of pain relief or increased drug toxicity.
Nalmefene must NEVER be used in the following circumstances (except for emergency overdose reversal where the benefit outweighs the risk):
These conditions require a careful risk-benefit analysis by a healthcare provider:
There is a potential for cross-sensitivity between nalmefene and other morphinan-derivative opioid antagonists, such as naltrexone or naloxone. If a patient has had a severe reaction to naltrexone, healthcare providers should exercise extreme caution when administering nalmefene.
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Nalmefene.
Nalmefene is classified under the older FDA Pregnancy Category C. There are no adequate and well-controlled studies of nalmefene in pregnant women. Animal studies have shown some evidence of embryotoxicity at very high doses.
It is not known whether nalmefene is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised. For the emergency nasal spray, breastfeeding is not a contraindication for use in an emergency. For chronic oral use, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Clinical studies of nalmefene did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. However, because elderly patients are more likely to have decreased hepatic, renal, or cardiac function, and may be taking multiple other medications (polypharmacy), the risk of drug interactions and side effects is higher. Dose selection should be cautious, usually starting at the low end of the dosing range.
Nalmefene and its glucuronide metabolite are excreted primarily by the kidney. In patients with end-stage renal disease, the half-life of nalmefene may be significantly prolonged. While the emergency dose is not adjusted, chronic use for alcohol dependence is not recommended in those with severe renal failure. It is not known if nalmefene is cleared by hemodialysis.
In patients with mild to moderate hepatic impairment, the clearance of nalmefene is reduced, and the half-life is increased. For alcohol dependence treatment, nalmefene is contraindicated in severe hepatic impairment. Healthcare providers should monitor liver enzymes periodically in patients with known liver disease who are taking this medication long-term.
> Important: Special populations require individualized medical assessment and close monitoring by a clinical team.
Nalmefene is a 6-methylene analogue of naltrexone. Its primary mechanism of action is as a competitive antagonist at the Mu (μ) and Delta (δ) opioid receptors. It has a very high binding affinity for the Mu receptor, which is responsible for the respiratory depressant effects of opioids. By displacing opioid agonists from these receptors, nalmefene reverses sedation and restores normal breathing.
Additionally, nalmefene acts as a partial agonist at the Kappa (κ) opioid receptor. This activity at the Kappa receptor is hypothesized to play a role in its efficacy for alcohol dependence by modulating the mesolimbic dopamine system (the brain's reward pathway), thereby reducing the reinforcing effects of alcohol consumption.
Following administration, nalmefene rapidly reverses the effects of opioids, including pupillary constriction (miosis), sedation, and respiratory depression. The onset of action for the nasal spray is approximately 2 to 5 minutes. Because of its long half-life, the duration of the opioid-blocking effect can last for several hours, often exceeding 8 to 12 hours. This provides a 'safety window' that is much longer than that of naloxone, potentially preventing the return of overdose symptoms as the offending opioid is metabolized.
| Parameter | Value |
|---|---|
| Bioavailability | ~100% (Nasal), ~40% (Oral) |
| Protein Binding | 45% |
| Half-life | 11 hours (Mean) |
| Tmax | 0.25 hours (Nasal), 1.5 hours (Oral) |
| Metabolism | UGT2B7 (Glucuronidation) |
| Excretion | Renal 75%, Fecal 20% |
Nalmefene is classified as an Opioid Antagonist. Within this class, it is grouped with medications like naloxone and naltrexone. Unlike naloxone, which is used strictly for emergency reversal, or naltrexone, which is used for maintenance of abstinence, nalmefene occupies a unique space due to its long duration and its specific application in reducing alcohol consumption.
Medications containing this ingredient
Common questions about Nalmefene
Nalmefene is primarily used for two distinct clinical purposes: the emergency reversal of opioid overdose and the reduction of alcohol consumption in adults with alcohol dependence. In the United States, it is FDA-approved as a high-dose nasal spray (OPVEE) to treat suspected opioid overdoses, including those caused by potent synthetic opioids like fentanyl. In the European Union, it is used as an oral tablet (Selincro) to help people with alcohol use disorder drink less. It works by blocking the receptors in the brain that respond to opioids and alcohol-induced chemicals. Because it lasts a long time in the body, it is especially effective at preventing the return of overdose symptoms.
The most common side effects of nalmefene include nausea, vomiting, dizziness, and headache. Many patients also report feeling tired or having trouble sleeping (insomnia) when they first start taking the medication. If the drug is given to someone who is currently using opioids, it will cause immediate and severe withdrawal symptoms like body aches, sweating, and diarrhea. These side effects are usually temporary but can be very uncomfortable. It is important to discuss any persistent or worsening side effects with a healthcare provider to ensure the medication is being used safely.
Yes, in the context of treating alcohol dependence, nalmefene is actually designed to be taken on days when you might drink alcohol. The goal of the medication is to reduce the amount of alcohol you consume by blocking the 'reward' or 'buzz' that alcohol provides. However, nalmefene does not prevent intoxication or the impairment of your coordination and judgment. You should still avoid driving or performing dangerous tasks if you have been drinking. It is not intended for people who need immediate medical detoxification from alcohol, as it does not prevent alcohol withdrawal symptoms like seizures.
The safety of nalmefene during pregnancy has not been fully established through clinical trials in humans. Animal studies have suggested some potential risks at very high doses, but it is not known if these apply to humans. In an emergency situation like an opioid overdose, nalmefene should be used because saving the mother's life is the highest priority for the health of both the mother and the baby. For the treatment of alcohol dependence, pregnant women should consult their doctor to weigh the risks and benefits. Generally, it is only used during pregnancy if the potential benefit clearly outweighs the potential risk to the developing fetus.
When administered as a nasal spray for an opioid overdose, nalmefene begins to work very quickly, usually within 2 to 5 minutes. Peak levels of the drug in the bloodstream are reached about 15 minutes after the spray is used. For the oral version used for alcohol dependence, it is typically taken 1 to 2 hours before you expect to drink to allow the drug to be absorbed. Because nalmefene has a long half-life of about 11 hours, its effects last much longer than naloxone, providing extended protection against the return of overdose symptoms. Always wait a few minutes between doses if the first spray does not seem to be working.
Nalmefene is not an addictive medication, and stopping it suddenly does not cause a physical withdrawal syndrome like opioids or alcohol do. However, if you are using it to manage alcohol dependence, stopping the medication may lead to an increase in your alcohol consumption as the protective 'blocking' effect wears off. If you are using it as part of a treatment plan, you should talk to your healthcare provider before making any changes. They can help you determine if it is the right time to stop and how to monitor your progress. Never stop taking a prescribed medication without medical guidance.
If you are taking nalmefene for alcohol dependence and you miss a dose, take it as soon as you remember, especially if you plan to drink alcohol that day. If you have already started drinking and realized you forgot your dose, you should still take the tablet as soon as possible. Do not take two doses at once to make up for the one you missed. If you are not planning to drink and you miss a dose, you can simply skip it and resume your normal schedule the next day. Consistency helps the medication work most effectively to reduce your overall alcohol intake.
Weight gain is not a commonly reported side effect of nalmefene in clinical trials. In fact, some medications that affect the opioid system, like naltrexone, are sometimes associated with weight loss or reduced appetite. Most patients taking nalmefene for alcohol dependence do not experience significant changes in their weight. If you notice unusual weight gain or loss while taking this medication, it may be related to other factors, such as changes in your diet or lifestyle as you reduce your alcohol consumption. Always discuss significant weight changes with your doctor to rule out other underlying health issues.
Nalmefene can interact with several types of medications, most notably opioid pain relievers. If you take Nalmefene with opioids like oxycodone or morphine, it will block their pain-killing effects and may cause withdrawal. It can also interact with certain liver enzymes, so it is important to tell your doctor about all the drugs you take, including over-the-counter supplements like St. John's Wort. While it doesn't have many 'dangerous' interactions with common drugs like antibiotics, your doctor needs to check for potential conflicts. Always provide a full list of your medications to your healthcare provider before starting nalmefene.
As of 2024 and 2025, nalmefene nasal spray (OPVEE) is a relatively new product and may still be under patent protection, meaning a generic version may not be immediately available in all markets. The oral version (Selincro) has been available in Europe for several years, and generic versions may be available in certain international jurisdictions. Generic availability often depends on the specific country's patent laws and the date the original brand-name drug was approved. You can check with your pharmacist or insurance provider to see if a lower-cost generic version of nalmefene is available for your specific prescription.