Narcan: Side effects and what to do about them

Narcan has one main job: to pull someone back from an opioid overdose. It does this fast, often in just a couple of minutes, and it’s now available over the counter in the United States as a 4 mg naloxone nasal spray.
That’s the lifesaving side of the story. But if you’ve ever seen Narcan usedor you’re thinking about keeping a box at homeyou might also wonder about the side effects and how to handle them without panicking.

The short version: Narcan is generally very safe, especially compared with an untreated opioid overdose. The most noticeable “side effect” is often opioid withdrawal in people who regularly use opioids. That can look intense and scary, but it’s usually temporary and manageable.

In this guide, we’ll walk through the most common Narcan side effects, the more serious but rare risks, and practical steps you can take in the moment. We’ll also look at real-world experiences so you know what to expect if you ever need to use it.

What is Narcan and how does it work?

Narcan is the brand name for naloxone, a medication that temporarily reverses the effects of opioids such as heroin, fentanyl, oxycodone, hydrocodone, morphine, and others. It works by kicking opioids off the brain’s opioid receptors and blocking them, which quickly improves breathing in an overdose.

Narcan nasal spray is now FDA-approved for over-the-counter (OTC) sale, meaning you don’t need a prescription to buy it.
It’s designed for everyday peoplefriends, family members, and bystandersto use in an emergency.

A few key points about how Narcan behaves in the body:

• It starts working within minutes but wears off in 30–90 minutes for most people.
• Many opioids last longer than Narcan, so multiple doses may be needed.
• If there are no opioids in the system, Narcan doesn’t usually cause major problemsanother reason experts say: “If you’re not sure, use it.”

How common are Narcan side effects?

Compared with many medications, Narcan’s side effect profile is actually pretty friendly. Most people either:

• Feel little or nothing special from the spray itself, or
• Wake up in rapid opioid withdrawal, which feels awful but is medically safer than continuing an overdose.

Official patient information and drug references list side effects like headache, nasal irritation, increased blood pressure, nausea, vomiting, and muscle or bone pain as possible reactions.
These are usually short-lived and overshadowed by the fact that the person is alive.

Common, usually mild Narcan side effects

1. Nose-related symptoms

Because Narcan is given as a nasal spray, some side effects show up right where it’s delivered:

• Nasal dryness or irritation
• Stuffy or runny nose
• Mild burning or discomfort in the nostril
• Rarely, a small amount of nosebleed

These effects are often reported in drug information from MedlinePlus, Mayo Clinic, and similar medical references.
They’re typically mild and go away on their own as the tissue calms down.

What you can do:

• Keep the person sitting up or in the recovery position to help drainage.
• Avoid sticking tissues or cotton swabs deep into the nose.
• Once they’re medically stable, a gentle saline spray (if recommended by a clinician) can be soothing.

2. Headache, dizziness, and feeling “off”

Headache is one of the most commonly reported Narcan side effects. Some people also feel dizzy, lightheaded, or just generally “weird” after waking up.

It’s hard to tease apart what’s from Narcan and what’s from the overdose, lack of oxygen, or other substances that might have been used at the same time. But in many cases, these symptoms ease over several hours.

What you can do:

• Make sure the person is in a safe place where they can lie or sit down without falling.
• Encourage slow, steady breathing; hyperventilating can worsen headache and dizziness.
• Let emergency medical providers know what was given and when; they may offer pain relief if it’s safe.

3. Nausea, vomiting, and stomach discomfort

Waking up from an overdose can make the body very unhappy, very quickly. Nausea, vomiting, stomach cramps, and diarrhea are well-documented symptoms of opioid withdrawal, and they’re often seen after Narcan use.

Why it happens: When naloxone suddenly blocks opioids, the nervous system reacts like someone yanked the emergency brake at highway speed. The gut is packed with opioid receptors, so it becomes overactivehence the nausea and diarrhea.

What you can do:

• Turn the person on their side (recovery position) to reduce the risk of choking if they vomit.
• Have a bowl or trash can nearby if they’re awake and alert.
• Let paramedics or ER staff know how much Narcan was used and what the person took, if known.

4. Muscle, bone, or body aches

Many people describe feeling like they were “hit by a truck” after Narcan. That’s not because the medication is toxic; it’s because opioid withdrawal often comes with intense muscle and bone pain, restlessness, and chills.

This is miserable, but it’s also a sign that the brain and body are waking up again.

What you can do:

• Offer blankets; people can feel very cold, then hot, then cold again.
• Create a calm environmentloud noises and bright lights can worsen agitation.
• Medical teams may use specific medications to help with withdrawal symptoms in a monitored setting.

5. Changes in blood pressure or heart rate

Narcan can cause increases in blood pressure and heart rate, especially in people who are dependent on opioids. Drug references and clinical reports mention tachycardia (fast heart rate), hypertension, sweating, and sometimes irregular heartbeat as possible reactions.

For most otherwise healthy people, these changes are temporary. But in someone with heart disease or other major medical problems, they do matterwhich is one reason emergency medical care is non-negotiable after using Narcan.

The big one: opioid withdrawal after Narcan

The most dramatic “side effect” of Narcan isn’t really a side effect at allit’s a consequence of rapidly reversing opioids in someone who is dependent on them. This is called precipitated withdrawal, and it can look intense.

What opioid withdrawal from Narcan can look like

Symptoms can include:

• Sudden, severe body aches and cramping
• Profuse sweating, chills, goosebumps
• Runny nose, watery eyes, yawning, sneezing
• Nausea, vomiting, diarrhea, stomach pain
• Fast heart rate and elevated blood pressure
• Anxiety, agitation, restlessness, irritability
• Rarely, seizures or heart rhythm problems in vulnerable people

Medical references like Mayo Clinic, Drugs.com, and StatPearls all describe this rapid-onset withdrawal picture after naloxone.

Why withdrawal feels so roughbut is still safer than overdose

Is withdrawal miserable? Absolutely. Is it worse than not breathing? Absolutely not.

An untreated opioid overdose can lead to brain damage, coma, or death. Narcan’s job is to pull the person out of that danger zone. The trade-off is that someone who is heavily dependent on opioids may wake up in full-blown withdrawal and be angry, confused, or uncomfortable.

This is why public health agencies and experts consistently say use Narcan if you suspect an overdose, even if you’re not 100% sure.

How long do withdrawal symptoms last?

Narcan itself doesn’t stay in the body very longusually under a couple of hours.
But:

• Some people improve significantly as Narcan wears off.
• Others may continue to feel sick because their underlying opioid use disorder is still present.
• In the ER, clinicians may start longer-acting treatments (like buprenorphine or methadone) to ease withdrawal and reduce the risk of another overdose.

Rare but important risks

Allergic reactions

True allergies to naloxone are rare but possible. The FDA label and other references mention reactions like rash, swelling, or trouble breathing as reasons to seek urgent care.
In real life, it’s often hard to tell if a rash or breathing issue is from Narcan or from the overdose and other drugs involved.

Red flag signs of a serious allergic reaction include:

• Swelling of the face, lips, tongue, or throat
• Trouble breathing or swallowing
• Hives or widespread rash

Again, this is another reason emergency services must be called every time Narcan is used.

Breathing and heart problems

In people with serious heart disease, very high blood pressure, or lung problems, the sudden stress of withdrawal can rarely trigger complications such as chest pain or pulmonary edema (fluid in the lungs).

These events are uncommon, but they’re important for clinicians to monitorwhich is why Narcan is never a “use it and walk away” situation.

Risks in infants and young children

Narcan is considered safe and effective in children and even infants when used for known or suspected opioid overdose.
However, the FDA warns that sudden withdrawal in newborns and very young infants who have been receiving opioids can be life-threatening if not treated appropriately.

If Narcan is used on a child, they should be evaluated and monitored by emergency professionals right awayno exceptions.

What to do about Narcan side effects (step by step)

If you just used Narcan on someone

Here’s the basic flow public health agencies like the CDC recommend after giving naloxone:

1. Call 911 immediately. Tell them that you suspect an opioid overdose and that Narcan has been given.
2. Give Narcan as directed on the package. One spray in one nostril. If there’s no response in 2–3 minutes, a second dose can be given in the other nostril if available.
3. Check breathing. If the person is not breathing or not breathing normally, start rescue breaths or CPR if you’re trained to do so.
4. Place them in the recovery position. Turn them on their side to reduce the risk of choking on vomit.
5. Stay with them. They may wake up confused, frightened, or in withdrawal. Speak calmly and explain what happened.
6. Be prepared for more doses. Fentanyl and some long-acting opioids may outlast Narcan.

Simple ways to ease mild side effects

Once emergency responders take over, they will focus on airway, breathing, circulation, and monitoring for complications. But if you’re with the person while waiting for help:

• Keep the environment calm and as quiet as possible.
• Offer reassurancemany people wake up scared and disoriented.
• Use blankets or extra layers if they’re shivering or have goosebumps.
• Don’t give food or drink right away if they’re nauseated or still very groggy.

When to call a healthcare professional after the emergency

After the immediate crisis passes, a follow-up with a healthcare professional is a crucial next step. A medical visit is especially important if:

• The person still feels unwell or short of breath hours after Narcan.
• There were chest pains, heart palpitations, or fainting.
• There are signs of infection, persistent nosebleeds, or ongoing headaches.
• The person is interested in treatment for opioid use disorder (a big opportunity for change).

Many clinics, health departments, and community programs can connect people to medications for opioid use disorder, counseling, and harm-reduction services.

Narcan myths about side effects, busted

Myth 1: “Narcan is dangerous if you give it to the wrong person.”

Reality: If someone does not have opioids in their system, Narcan usually does very little. You won’t accidentally “overdose” someone on Narcan. Medical references and public health guidance repeatedly emphasize that it’s better to give it when you’re unsure than to hold back.

Myth 2: “Narcan side effects are worse than the overdose.”

Reality: Withdrawal symptoms can be harsh, but they are survivable. Lack of oxygen from an overdose, on the other hand, can cause brain damage or death in minutes. That’s not a fair comparisonNarcan wins every time.

Myth 3: “Narcan encourages people to use more drugs.”

The idea that Narcan “enables” overdose is not supported by the best available public health data. Communities that expand naloxone access often see lower overdose death rates, not higher.
In other words, Narcan doesn’t cause addictionit keeps people alive long enough to get help.

Real-world experiences: what Narcan side effects feel like in everyday life

Statistics and side effect lists are useful, but they don’t always capture what Narcan actually feels like in the real world. While everyone’s experience is unique, here’s a composite picture based on common stories from first responders, family members, and people who live with opioid use disorder.

From the bystander’s perspective

Imagine you’re a friend at a small get-together. One person starts to nod out, then stops responding. Their breathing slows, their lips look a little bluish. You’ve seen the posters about overdoses, so you checkbarely any breathing. Your heart jumps into your throat.

You grab the Narcan kit someone picked up at the pharmacy “just in case.” You tilt their head back, give the spray, and call 911 with hands that suddenly feel too big and clumsy. For the longest 2 minutes of your life, nothing happens. Then they gasp, cough, and bolt upright, looking furious, confused, and sick.

They start complainingloudlyabout feeling horrible. Their stomach cramps, they’re sweating and shaking, they’re nauseated and maybe vomiting into a trash can. You’re relieved they’re alive, but also startled at how rough this looks. You keep repeating, “You overdosed. We gave you Narcan. Help is on the way.”

The side effects you’re seeingvomiting, sweating, agitationare classic signs of sudden withdrawal. From your perspective, it looks chaotic. From a medical perspective, it’s actually expected and treatable.

From the person who received Narcan

Many people who have been revived with Narcan describe the experience like this: one moment, nothing; the next, they wake up feeling as if every bone and muscle hurts. Their skin is clammy, they can’t get comfortable, and their stomach is doing somersaults. They may feel panicky, angry that their “high” is gone, or ashamed that the overdose happened at all.

It’s also common to feel confused about time. They might think only a few seconds passed, when in reality several minutesor morewent by without adequate breathing. On top of that, bright lights, multiple people talking at once, and the siren of an arriving ambulance can quickly overload the senses.

Those side effectsespecially withdrawalcan last for hours, even after Narcan itself has mostly worn off, because they’re tied to the underlying opioid dependence. For some, that miserable window becomes a turning point: the moment they decide they never want to be that close to death again.

From the first responder’s viewpoint

Paramedics, firefighters, and police officers who respond to overdoses see Narcan’s effects all the time. Their main concerns are:

• Is the person breathing?
• Do we need more Narcan?
• Are there other drugs involvedlike alcohol, benzodiazepines, or stimulants?
• Are there medical complications (trauma, heart problems, aspiration of vomit)?

They expect side effects such as agitation, vomiting, sweating, and high blood pressureit’s part of the job. They also know some people will be grateful and others might be angry. Either way, Narcan gives them a fighting chance to stabilize the patient and get them to the hospital.

From communities and families

For families and communities, Narcan’s side effects are often weighed against a heavier memory: funerals that didn’t have to happen. Parents who keep a box of Narcan in their bathroom, librarians who quietly stock it in their first-aid kit, people in recovery who carry it not just for themselves but for strangersall of them have decided that a few minutes of withdrawal, headache, or a sore nose is a small price to pay for another day of life.

In that light, the “side effects” of Narcan include something bigger: a second chance. And while the drug can’t fix addiction, housing, or trauma on its own, it can create the space where change is still possible.

The bottom line

Narcan (naloxone) is a powerful, fast-acting medication that can reverse an opioid overdose and restore breathing within minutes. Its side effects are usually:

• Mild and local, like nose irritation or headache, or
• Related to sudden opioid withdrawal, which feels awful but is still far safer than an untreated overdose.

Serious complicationslike heart problems, severe allergic reactions, or dangerous withdrawal in newbornsare possible but rare and typically occur in people with significant underlying medical issues. That’s why emergency medical care is always necessary after Narcan use.

If you live in an area affected by opioids, keeping Narcan on hand is like keeping a fire extinguisher in the kitchen: you hope you never need it, but if you do, it can save a life. Knowing the side effects and how to handle them makes you better preparednot just to help, but to stay calm when it matters most.

This article is for general education only and does not replace medical advice from a licensed healthcare professional. If you have questions about Narcan or opioid use, talk with a healthcare provider or local harm-reduction program.