Naloxone (brand names Narcan and Kloxxado) is an opioid antagonist that rapidly reverses opioid overdose by competitively displacing opioids from mu-opioid receptors in the brain and brainstem. It restores breathing within two to five minutes when administered as a nasal spray or injection, and it has no potential for abuse or dependence. In 2023, the FDA approved over-the-counter naloxone nasal spray (Narcan 4 mg), making this life-saving medication available without a prescription. Naloxone works on all opioids including heroin, fentanyl, oxycodone, and methadone, though fentanyl overdoses may require multiple doses due to fentanyl’s exceptionally high receptor-binding affinity.
Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Phuket Island Rehab
“Naloxone is the single most important harm reduction tool in opioid medicine,” says Dr. Ponlawat Pitsuwan. “At Phuket Island Rehab, we ensure that every patient completing opioid treatment leaves with naloxone training and access, because the period immediately following treatment carries elevated overdose risk due to reduced tolerance. Understanding how to use naloxone correctly, and understanding its limitations, is information that can mean the difference between life and death.”
How Naloxone Works at the Receptor Level
Naloxone is a competitive antagonist at mu-opioid receptors (MOR), kappa-opioid receptors, and delta-opioid receptors, with its highest affinity for the mu receptor. When an opioid such as heroin or fentanyl occupies mu-opioid receptors in the pre-Bötzinger complex of the brainstem, it suppresses the neural circuits that generate automatic breathing rhythm, causing respiratory depression. Naloxone works by binding to these same receptors with higher affinity than the opioid, physically displacing the opioid molecules and restoring normal receptor function.
This competitive displacement mechanism means naloxone does not degrade or destroy the opioid molecules in the body. They remain in circulation and can re-occupy the receptors once the naloxone is metabolised. This is why renarcotisation (returning to overdose after naloxone wears off) is a clinical reality, particularly with long-acting opioids like fentanyl and methadone. Naloxone’s duration of action is approximately 30 to 90 minutes, while many opioids persist in the body for hours.
Naloxone has no opioid agonist activity whatsoever, meaning it produces no euphoria, no respiratory depression, and no dependence. In a person without opioids in their system, naloxone has essentially no clinical effect. This safety profile is what allows it to be administered by bystanders without medical training, as giving naloxone to someone who is not experiencing an opioid overdose will not harm them.
Available Naloxone Formulations
| Formulation | Dose | Route | Onset | Key Advantage |
|---|---|---|---|---|
| Narcan nasal spray | 4 mg per spray | Intranasal | 2 to 5 minutes | OTC availability, no needles, easiest for bystanders |
| Kloxxado nasal spray | 8 mg per spray | Intranasal | 2 to 5 minutes | Higher dose for fentanyl overdoses |
| Injectable naloxone (prefilled syringe) | 0.4 mg per mL | Intramuscular or subcutaneous | 2 to 5 minutes (IM) | Lower cost, allows dose titration |
| Auto-injector (Evzio, discontinued) | 0.4 mg or 2 mg | Intramuscular | 2 to 5 minutes | Voice-guided instructions (discontinued from market) |
| IV naloxone (hospital setting) | 0.04 to 0.4 mg increments | Intravenous | 1 to 2 minutes | Fastest onset, precise dose titration |
Step-by-Step: How to Use Narcan Nasal Spray
Using Narcan nasal spray requires no medical training. The device is pre-assembled and ready to use out of the package. First, call emergency services immediately if you suspect an opioid overdose. While waiting for help, lay the person on their back. Tilt their head back and support the neck to open the airway. Hold the Narcan device with your thumb on the bottom of the plunger and two fingers on the nozzle. Insert the nozzle into one nostril until your fingers touch the bottom of the person’s nose. Press the plunger firmly to deliver the full dose. Each device contains a single dose and cannot be reused.
If the person does not respond within two to three minutes, administer a second dose in the opposite nostril using a new device. Continue monitoring breathing and be prepared to administer additional doses if available. Place the person in the recovery position (on their side with the top knee bent forward) to prevent aspiration if they vomit. Stay with the person until emergency medical services arrive, even if they appear to recover, because the naloxone may wear off before the opioid does.
Warning: A person who has been revived with naloxone should always receive medical evaluation. Naloxone’s duration of action (30 to 90 minutes) is shorter than most opioids, meaning the person can slip back into overdose once the naloxone wears off. This is especially dangerous with fentanyl and methadone, which persist in the body for hours. Never leave a naloxone-revived person alone.
Naloxone and Fentanyl: Why Multiple Doses May Be Needed
Fentanyl’s exceptionally high binding affinity at the mu-opioid receptor means that naloxone must compete against a stronger bond than it faces with heroin or prescription opioids. While a single 4 mg Narcan dose is typically sufficient for heroin overdose, fentanyl overdoses frequently require two, three, or even more doses administered at two to three minute intervals. The higher-dose Kloxxado (8 mg) nasal spray was developed specifically for this clinical reality.
The renarcotisation risk is also elevated with fentanyl because fentanyl accumulates in fat tissue and is released slowly over hours. Even after successful naloxone reversal, the person may re-enter respiratory depression as the naloxone is metabolised and the stored fentanyl continues to release. This is why hospital observation is critical after any suspected fentanyl overdose reversal, and why carrying multiple naloxone doses is recommended in fentanyl-affected communities.
What to Expect When Naloxone Takes Effect
When naloxone successfully reverses an opioid overdose, the person will typically begin breathing more deeply and regularly within two to five minutes. They may become agitated, confused, or combative as they are abruptly thrust into opioid withdrawal. Symptoms can include nausea, vomiting, sweating, tachycardia, elevated blood pressure, tremor, and severe anxiety. The person may not understand what happened and may be distressed or angry. This response is a normal pharmacological consequence of rapid opioid displacement and does not indicate that something has gone wrong.
It is important to understand that the person has not chosen to enter withdrawal. Their body has been chemically forced from opioid receptor saturation to opioid receptor vacancy within minutes. This is physiologically jarring and psychologically distressing. Approach the person with calm reassurance, explain what happened, and ensure they receive medical attention. Some individuals may want to use opioids again to relieve the precipitated withdrawal, which creates a dangerous situation if they do so while naloxone is still partially active and their respiratory drive is compromised.
Clinical insight: In hospital emergency departments, IV naloxone is titrated in small increments (0.04 to 0.1 mg) to restore breathing without precipitating full withdrawal. This careful titration is not possible in community settings where nasal spray delivers a fixed 4 mg dose, which is why precipitated withdrawal symptoms are common after bystander-administered naloxone. The discomfort of precipitated withdrawal, while unpleasant, is vastly preferable to death from respiratory arrest.
Who Should Carry Naloxone
Naloxone should be carried by anyone who uses opioids (prescribed or otherwise), anyone who lives with or regularly spends time with someone who uses opioids, family members of people with opioid use disorder, first responders and law enforcement, staff at shelters and social service organisations, and anyone who may encounter opioid overdose in their community. The expanded availability of over-the-counter Narcan has removed the prescription barrier in many countries, making it accessible through pharmacies without a doctor’s visit.
People completing opioid treatment are at particularly elevated overdose risk because their tolerance has decreased during treatment. If they return to use at their pre-treatment dose, the now-sensitised brain cannot tolerate the same amount. This post-treatment period, particularly the first two weeks after discharge from detoxification or residential treatment, carries the highest overdose risk in the entire addiction trajectory. Naloxone availability during this vulnerable period is a critical safety measure.
When Substance Use Has Become More Than Occasional
If you or someone you know requires naloxone, that event should serve as a clear clinical signal that opioid use has reached a dangerous level. An overdose is not a random event; it is a consequence of opioid use disorder at a severity level that has become life-threatening. While naloxone saves the immediate moment, it does not treat the underlying condition. The period following an overdose reversal represents both a medical necessity and a window of opportunity to initiate treatment for opioid use disorder.
Evidence-based treatments for opioid use disorder, including medication-assisted treatment with buprenorphine, methadone, or naltrexone, combined with therapeutic support, offer paths to sustained recovery. Residential treatment programmes like Phuket Island Rehab provide the medical supervision and structured environment needed for safe detoxification and the comprehensive therapeutic work that supports long-term change.
Summary
Naloxone is a safe, effective, and increasingly accessible medication that reverses opioid overdose by competitively displacing opioids from brain receptors and restoring breathing. Its over-the-counter availability as Narcan nasal spray means that anyone can carry and administer this life-saving tool without medical training. In the era of fentanyl, multiple doses may be needed, and post-reversal medical monitoring is essential because naloxone wears off before many opioids do. Every person at risk of witnessing or experiencing an opioid overdose should have naloxone accessible and know how to use it.
“Naloxone gives us time,” says Dr. Ponlawat Pitsuwan. “It reverses the immediate threat of respiratory arrest and creates a window in which treatment, connection, and recovery become possible. But it is a bridge, not a destination. The work that follows, addressing the opioid use disorder that led to the overdose, is what transforms a saved life into a changed one. At Phuket Island Rehab, we see that transformation regularly, and it begins with the understanding that recovery from opioid dependence is both possible and achievable.”
Frequently Asked Questions
Can naloxone harm someone who has not taken opioids?
No. Naloxone has no opioid activity and produces no clinical effect in a person without opioids in their system. If you suspect someone may be overdosing and administer naloxone but the cause is not opioid-related (for example, a stimulant overdose, diabetic emergency, or seizure), the naloxone will not help but it will not cause harm either. This safety profile is what allows naloxone to be administered by bystanders without risk. When in doubt, administer naloxone and call emergency services.
Does naloxone expire?
Yes, naloxone has an expiration date printed on the packaging, typically 18 to 24 months from manufacture. However, research published in the Journal of General Internal Medicine found that expired naloxone retains significant potency well beyond its labelled expiration date. If you are in an emergency situation and only have expired naloxone, use it. An expired dose is far better than no dose. Replace expired naloxone when possible, but do not discard it until you have a current supply to replace it with.
Is naloxone the same as naltrexone?
No. Both are opioid antagonists but they serve very different purposes. Naloxone is a short-acting antagonist used for acute overdose reversal, with effects lasting 30 to 90 minutes. Naltrexone is a long-acting antagonist used for relapse prevention in opioid and alcohol use disorders, with daily oral formulations or monthly injections (Vivitrol) that provide sustained receptor blockade. Naloxone is administered in emergencies; naltrexone is taken as part of ongoing treatment after detoxification is complete.
Can I get in legal trouble for administering naloxone?
In the United States and many other countries, Good Samaritan laws provide legal protection for individuals who administer naloxone in good faith during a suspected overdose. These laws also typically protect the overdose victim from prosecution for drug possession. The specifics vary by jurisdiction, but the trend globally is toward expanding legal protections for bystander naloxone use. The moral and ethical imperative to save a life takes precedence, and legal frameworks increasingly reflect this principle.
How do I store naloxone properly?
Narcan nasal spray should be stored at room temperature (20 to 25°C or 68 to 77°F) in its original packaging to protect it from light. It should not be exposed to temperatures above 40°C (104°F) or left in a hot car for extended periods. Do not freeze naloxone. If you carry it in a purse, backpack, or first aid kit, periodic temperature exposure is generally acceptable, but avoid prolonged extreme heat. Check the expiration date periodically and replace as needed.
Why might someone need naloxone more than once?
Multiple naloxone doses may be needed for two reasons. First, if the initial dose is insufficient to displace a potent opioid like fentanyl from the receptors, additional doses increase the competitive displacement. Second, because naloxone has a shorter duration of action than most opioids, a person who initially responds to naloxone may re-enter overdose (renarcotisation) when the naloxone is metabolised but the opioid remains active. This is particularly common with fentanyl and methadone, both of which persist in the body long after naloxone wears off, requiring extended medical monitoring.
Sources
US Food and Drug Administration. “FDA Approves First Over-the-Counter Naloxone Nasal Spray.” 2023. fda.gov
Substance Abuse and Mental Health Services Administration (SAMHSA). “Naloxone.” samhsa.gov
National Institute on Drug Abuse (NIDA). “Naloxone DrugFacts.” National Institutes of Health. drugabuse.gov
Naloxone · Narcan · Kloxxado · Opioid antagonist · Mu-opioid receptor · Competitive displacement · Renarcotisation · Respiratory depression · Pre-Bötzinger complex · Precipitated withdrawal · Fentanyl · Heroin · Methadone · Buprenorphine · Naltrexone · Vivitrol · Good Samaritan laws · Opioid use disorder · Phuket Island Rehab