Naloxone (Narcan)

What it treats

Naloxone is approved by the U.S. Food and Drug Administration for the emergency treatment of known or suspected opioid overdose, as manifested by respiratory depression or unresponsiveness.

That's it. It doesn't reduce cravings, doesn't help people stop using, doesn't treat pain. It reverses an overdose long enough for the person to breathe again and for emergency medical services to get there. The medications that treat opioid use disorder (buprenorphine, methadone, extended-release naltrexone) are separate.

How it works

Opioids kill people by suppressing the brainstem drive to breathe. Naloxone binds to the same µ (mu) opioid receptor that opioids bind, but it has no agonist effect of its own. It just displaces the opioid. When you give naloxone to someone in respiratory depression from an opioid, the drug essentially yanks the opioid off the receptor, breathing comes back, and consciousness returns within a couple of minutes.

The problem is that naloxone's effect is short. It wears off in 30 to 90 minutes. Most opioids people overdose on, especially fentanyl, last longer than that. So a person can wake up, seem fine, and then re-overdose as naloxone wears off. That's why calling 911 is a required part of every naloxone use.

Receptor mechanism (detail)

Naloxone is a competitive antagonist at the µ-opioid receptor, with weaker antagonism at the κ (kappa) and δ (delta) receptors. It has essentially no agonist activity of its own. In a person who's not opioid-dependent, naloxone does nothing noticeable. In a person with opioids on board, it reverses their effects. In a person who's opioid-dependent, it precipitates withdrawal.

Potency and typical dosing pattern

Ranges are typical framework only, not a prescription for any individual.

For bystander rescue, the standard is one dose of intranasal naloxone (4 mg or 8 mg per spray depending on product) into one nostril. If there's no response in 2 to 3 minutes, give a second dose in the other nostril. Continue every 2 to 3 minutes until the person is breathing or EMS arrives.

For medical settings, IV or IM naloxone at 0.4 mg is standard, with additional doses as needed. Onset is 2 to 3 minutes intranasal or IM, faster IV. Effect lasts about 30 to 90 minutes.

Safety monitoring

• Breathing and consciousness during and after the reversal. Support breathing (rescue breaths or bag-mask) if trained.
• Repeat dosing if the person doesn't respond in 2 to 3 minutes or if they go back into respiratory depression as naloxone wears off.
• Call 911 every single time, even if the person wakes up and feels okay. The opioid may outlast the naloxone.
• Precipitated withdrawal symptoms, which are unpleasant but not dangerous in most healthy people.
• Watch for vomiting and turn the person onto their side so they don't aspirate.

What to expect

Naloxone works fast. Within 1 to 3 minutes of a nasal spray, someone in overdose usually starts breathing more normally and becomes responsive. They often feel awful when they wake up: sweating, nauseated, agitated, muscles aching, sometimes vomiting. That's precipitated withdrawal, and it's expected in anyone opioid-dependent.

The reversal is temporary. Depending on how much and what kind of opioid is on board, the person can slide back into respiratory depression as naloxone wears off. That's the single most important thing to know: don't leave the person alone, and don't cancel EMS just because they're awake.

Common side effects

In a person without opioid dependence, side effects are minimal.

In a person with opioid dependence, precipitated withdrawal is expected and can include:

• Sweating.
• Nausea and vomiting.
• Agitation and anger.
• Body aches and muscle cramps.
• Rapid heart rate and elevated blood pressure.
• Runny nose and tearing.

These are uncomfortable but not typically dangerous. They usually settle within 30 to 60 minutes as the naloxone wears off.

Serious side effects and warnings

Serious problems from naloxone itself are rare, but a few situations matter.

• Rebound respiratory depression. As naloxone wears off, if the underlying opioid is still on board and long-acting, the person can stop breathing again. Repeat dosing and EMS are essential.
• Precipitated withdrawal in pregnancy can cause fetal distress. That said, the alternative is maternal death from overdose, so naloxone should still be given if a pregnant person is overdosing.
• Pulmonary edema and arrhythmias have been reported rarely, mostly after opioid reversal in cardiac patients.
• Combativeness on waking, occasionally, which is a safety issue for the rescuer.
• Rebound overdose after acute reversal, especially with fentanyl and its analogues, which can outlast several doses of naloxone.

Sexual and relational effects

Naloxone doesn't have chronic effects because it's used briefly during rescue. On the relational side, the important thing is that carrying naloxone is one of the most concrete acts of care someone can offer a family member or friend who uses opioids. Having it in the house, the car, or the bag doesn't cause harm and can save a life.

Weight, appetite, and sleep

Not applicable in any meaningful way. Naloxone is a rescue medication given for minutes, not a daily medication.

Starting and dosing basics

This section is general background, not a dosing instruction for any individual. When and how to use naloxone in a real situation is what the label and community trainings walk through.

Naloxone comes in several forms: 4 mg and 8 mg intranasal sprays (Narcan and generics), an IM auto-injector, and standard IM/SC/IV vials. For bystander rescue, the intranasal spray is by far the easiest. Give one spray in one nostril while the person is on their back. If no response in 2 to 3 minutes, give another spray in the other nostril. Repeat until EMS arrives.

Since 2023, Narcan nasal spray is available over the counter in the U.S. Many pharmacies also participate in standing order programs that let anyone pick it up without a prescription.

Missed doses and interactions

Naloxone isn't a scheduled medication, so there's no dose to miss. The relevant interaction is with opioids themselves: naloxone reverses the effect of any full or partial opioid agonist, including heroin, fentanyl, oxycodone, morphine, methadone, and buprenorphine.

In a person on buprenorphine or methadone for OUD, if they overdose on something else and get naloxone, the naloxone will also displace their maintenance opioid, which will hurt but won't do lasting harm. Resume the maintenance medication afterward.

Stopping and tapering

Not applicable. Naloxone isn't taken chronically.

Pregnancy and breastfeeding

Pregnant people can and should receive naloxone during opioid overdose. Precipitated withdrawal can stress the fetus, but maternal death from overdose is worse. There is no situation where withholding naloxone during overdose is safer than giving it. Breastfeeding after naloxone use isn't a concern because so little of it enters milk and it isn't absorbed orally.

Anyone who is pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber so the specific risks and benefits can be weighed.

Cost and generic availability

Naloxone nasal spray is available over the counter in the U.S. for around $45 for a two-pack. Many states have laws requiring pharmacies to stock it. Many public health departments, harm reduction organizations, and community programs distribute it free. Generic intranasal naloxone is available. Kloxxado is an 8 mg version. Zimhi is a higher-dose intramuscular auto-injector.

Common questions

Can I hurt someone by giving them naloxone if they're not overdosing? No. If there's no opioid on board, naloxone does essentially nothing. If you're not sure whether it's an overdose, give it anyway.

Do I still need to call 911 if the person wakes up and feels okay? Yes. Naloxone wears off in 30 to 90 minutes. The opioid that caused the overdose can outlast that, and the person can go back into respiratory depression. Every state has some form of Good Samaritan law that protects bystanders and the overdosing person from arrest for drug-related charges when they call for help.

Will they be angry when they wake up? Sometimes, yes. Precipitated withdrawal is unpleasant, and the person may be confused or upset. Stay calm, tell them what happened, and wait for EMS.

Who should carry it? Anyone taking opioids for pain or in OUD treatment. Anyone whose family member or friend uses opioids. Anyone who spends time in settings where opioid overdose happens. That's most of us.

Does it work on fentanyl? Yes. Fentanyl often needs more than one dose because it's so potent and can outlast one round of naloxone. Keep giving doses every 2 to 3 minutes until the person is breathing or EMS arrives.

Questions to ask your prescriber

• Should I have naloxone at home based on my medications or my family's?
• Which form is best for my situation, and how do I use it?
• Who else in my household should be trained to use it?
• Where can I get free or low-cost naloxone in my area?
• If I use it on someone, what do I do afterward?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes, and current as of June 8, 2026.

• U.S. Food and Drug Administration. Naloxone (Narcan) prescribing information and OTC approval.
• DailyMed, U.S. National Library of Medicine. Naloxone hydrochloride label.
• MedlinePlus, U.S. National Library of Medicine. Naloxone.
• Substance Abuse and Mental Health Services Administration. Opioid overdose prevention toolkit.
• American Society of Addiction Medicine. Guidance on naloxone in overdose response.
• Centers for Disease Control and Prevention. Naloxone information and overdose prevention.