Side Effects of Narcan: What You Need to Know

Narcan (naloxone) is a nasal spray that treats opioid overdose in adults and children. It’s possible to have mild or serious side effects from Narcan treatment.

An opioid overdose occurs when someone accidentally or intentionally takes more opioids than their body can safely process. (Opioids are very strong pain medications, such as oxycodone or morphine.) Opioid overdose is a medical emergency that causes slow, weak breathing and loss of consciousness. This can be fatal if not treated.

Narcan temporarily reverses the effects of an opioid overdose while you wait for emergency medical treatment. It can be purchased from a pharmacy without a prescription. If you experience an opioid overdose, you won’t be able to give Narcan to yourself. It’s meant to be given by someone else.

It’s important to note that Narcan is not a substitute for medical treatment. After giving Narcan to someone, call 911 right away, even if the person wakes up after getting Narcan.

Narcan can be very effective for treating an opioid overdose. For more information about Narcan, see this in-depth article on the drug.

Keep reading to learn more about the possible side effects (sometimes called “after effects”) of Narcan.

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Note: In March 2023, the Food and Drug Administration (FDA) approved Narcan for over-the-counter (OTC) use. This means you’ll be able to buy Narcan off the shelf, without consulting with a pharmacist. Narcan is not yet available for OTC purchase in pharmacies, but it’s expected to become available later in 2023.

Some people may experience mild or serious side effects during their Narcan treatment. Examples of side effects most commonly reported with Narcan include:

• dryness in the nose*
• stuffy nose
• pain in the muscles or bones*
• headache*
• opioid withdrawal symptoms in people who are physically dependent on opioids*

Read on to learn about some possible mild and serious side effects of Narcan.

* To learn more about this side effect, see “Side effects explained” below.

Narcan can cause mild side effects in some people. Examples of mild side effects that have been reported include:

• dryness or pain in the nose*
• stuffy nose*
• pain in the muscles or bones*
• headache*
• increased blood pressure
• muscle spasms
• toothache
• dry skin
• opioid withdrawal symptoms in people who are physically dependent on opioids*

* To learn more about this side effect, see “Side effects explained” below.

It’s important to note that except for dryness or pain in the nose, the above side effects would only occur in someone who’s used opioids before receiving Narcan. (Dryness or pain in the nose can occur in anyone receiving Narcan because the drug is given through the nose.)

In most cases, mild side effects should be temporary. And some may be easily managed, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist.

Narcan may cause mild side effects other than the ones listed above. To learn more, see Narcan’s prescribing information.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Narcan, visit MedWatch.

Some people may experience serious side effects after using Narcan. Serious side effects that have been reported with Narcan include:

• severe opioid withdrawal symptoms in people who are physically dependent on opioids*
• allergic reaction*†

It’s important to note that the side effects listed above would only occur in someone who’s used opioids before receiving Narcan.

If you develop serious side effects after receiving Narcan, call your doctor right away. If the side effects seem life threatening or if you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see “Side effects explained” below.
† An allergic reaction is possible after using Narcan. However, it’s not clear whether this side effect occurred in studies.

Below you can find answers to some frequently asked questions about Narcan’s side effects.

Does Narcan interact with any other drugs?

Narcan blocks the effects of opioid drugs, but it’s not known to interact with other drugs. However, some side effects of Narcan may be more likely in people who use certain other drugs.

For example, Narcan can sometimes cause severe opioid withdrawal symptoms that lead to serious heart problems, including heart rhythm problems and heart attack.

You may have a higher risk for heart problems from Narcan if you use other drugs that can also cause heart problems. (To learn more about opioid withdrawal symptoms, see the “Side effects explained” section below.)

When you purchase Narcan from the pharmacy, talk with your pharmacist. Tell them about all prescription, over-the-counter, and other drugs you take. Also tell them about any vitamins, herbs, and supplements you use. Sharing this information can help you avoid potential interactions.

If you have questions about drug interactions that may affect you, ask your doctor or pharmacist.

How long does Narcan stay in your system?

Narcan stays in your system for about 2 hours. If you have questions about how your body eliminates Narcan, talk with your doctor or pharmacist.

For information on how long side effects from Narcan last, see the question below.

What effect does Narcan have on someone who doesn’t need it?

Narcan won’t have any effect on someone who doesn’t need it (someone who does not have opioids in their body). So it’s safe to give someone Narcan if you think they may have overdosed on opioids but aren’t sure.

How long do side effects from Narcan last?

Side effects from Narcan typically go away within a couple of hours. If you have particularly severe side effects, your emergency medical team may give you treatment to help relieve them more quickly.

Does Narcan cause any long-term side effects?

No, Narcan is not known to cause any long-term side effects. If you have questions about how long potential side effects from this drug may last, talk with your doctor or pharmacist.

Is Narcan given as a shot? If so, what are its side effects?

No, Narcan isn’t given as a shot. It’s only available as a nasal (nose) spray. However, naloxone (the active drug in Narcan) is given as an injection. The naloxone injection is typically used in healthcare settings such as hospitals.

The main side effects of naloxone injection are opioid withdrawal symptoms similar to those seen with Narcan. To learn more, see the “Side effects explained” section below. The naloxone injection may also cause reactions at the site where the injection is given.

The possible side effects of Narcan in children who have ingested opioids are similar to those seen in adults. However, Narcan may cause more severe opioid withdrawal symptoms in newborns than in older children or adults given the medication. These symptoms can be life threatening for newborns if they’re not treated right away by medical professionals.

To learn about opioid withdrawal symptoms that both adults and children of all ages can experience, see “Side effects explained” below.

Additional opioid withdrawal symptoms in newborns can include:

• seizures
• crying more than usual
• increased reflexes, which may cause twitching or shakiness
• very fast breathing
• vomiting

If a newborn ingests Narcan, call 911 right away. The emergency medical team will give the newborn the appropriate treatment to help them recover from opioid withdrawal symptoms. The child will then need to be monitored in the hospital for at least 24 hours after receiving Narcan.

Below, you can learn more about some of the side effects Narcan may cause.

It’s important to note that although Narcan may cause side effects in some people, an opioid overdose can be fatal. Using Narcan can save someone’s life. You shouldn’t delay giving Narcan to treat an opioid overdose because of concerns about side effects.

And keep in mind that the active drug in Narcan doesn’t affect people who haven’t used opioids. So you can safely give Narcan to someone if you think they may have overdosed on opioids but aren’t sure.

Opioid withdrawal symptoms

Sudden opioid withdrawal symptoms can occur right after someone is treated with Narcan. This is because Narcan blocks and reverses the effects of opioids in the body.

Narcan commonly causes opioid withdrawal symptoms in people who are physically dependent on opioids. With physical dependence, your body needs opioids to function like usual.

Physical dependence can develop in someone who’s been taking opioids regularly for a long time. In this situation, if opioids are stopped or their effects are blocked by Narcan, it causes withdrawal symptoms.

Opioid withdrawal symptoms caused by Narcan can be mild or severe. Examples of these symptoms include:

• serious heart problems, such as heart rhythm problems or heart attack*
• nausea and vomiting
• diarrhea
• body aches or cramps
• shivering or goosebumps
• runny nose or sneezing
• fever or sweating
• increased blood pressure
• fast heart rate
• feeling irritable or nervous
• aggressive behavior

* These serious heart problems have typically occurred in people with heart disease who received Narcan after an operation or procedure. They’ve also occurred in people who receive Narcan and are also taking other drugs that can affect the heart. If you’re concerned about heart problems with Narcan, talk with your doctor or pharmacist.

What might help

If you’ve given someone Narcan, call 911 right away. When the emergency medical team arrives, they can give the person treatment to help them recover from opioid withdrawal symptoms if needed.

Opioid withdrawal symptoms can sometimes lead someone who is physically dependent on opioids to take more opioids. This can be very dangerous and lead to another overdose. After an opioid overdose has been treated, it’s also important that the person receives advice about treatments for opioid use disorder.

Nasal dryness, pain, or stuffy nose

Receiving Narcan may cause dryness or pain in the nose. It may also cause a stuffy nose. These side effects have been reported in people using the drug, although it isn’t clear whether they’re common or how often they happen.

What might help

Nose-related side effects will typically wear off within a few hours after receiving Narcan. However, if these side effects are bothersome to you, talk with a healthcare professional. They may be able to help relieve these side effects.

Headache or pain in your muscles or bones

Someone who’s received Narcan may experience pain, such as a headache or pain in their muscles or bones. These types of pain have been reported in people who received Narcan, although it isn’t clear how often or whether they’re common.

Narcan blocks and reverses all the effects of opioids, including the pain relief these drugs provide. Therefore, any pain someone had before using opioids may quickly come back after they’re given Narcan.

What might help

If you’ve given someone Narcan, call 911 right away. After the emergency medical team has treated the person’s overdose, they can treat their pain if needed.

The person who received Narcan shouldn’t take opioids for pain after receiving Narcan. This can cause them to overdose again.

If you experience an opioid overdose, your doctor can determine what the best treatment plan is for you.

Allergic reaction

Like most drugs, Narcan can cause an allergic reaction in some people. However, it’s not clear whether this side effect occurred in studies of the drug.

Symptoms of an allergic reaction can be mild or serious and may include:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)
• swelling under your skin, typically in your eyelids, lips, hands, or feet
• swelling of your mouth, tongue, or throat, which can make it hard to breathe

Serious allergic reactions, such as swelling or trouble breathing, could be life threatening and require immediate medical care.

What might help

If you’ve given someone Narcan, call 911 right away. After treating the person’s overdose, the emergency medical team can treat an allergic reaction if needed.

If your doctor confirms you had an allergic reaction to Narcan, they’ll decide if you can be given this drug in the future.

Narcan may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor or pharmacist about your health history before you take Narcan. Factors to consider include those in the list below.

Allergic reaction. If you’ve had a past allergic reaction to Narcan or any of its ingredients, you shouldn’t take Narcan. Ask your doctor what other medications are better options for you.

Heart disease. Someone with heart disease could be at risk for serious heart problems if they’re given Narcan, especially if they take certain medications for their condition. Examples include heart rhythm problems or heart attack. For more information, see the “Side effects explained” section above. If you have a heart problem, talk with your doctor or pharmacist about whether Narcan is right for you.

Alcohol and Narcan

Narcan can be used to treat an opioid overdose in someone who has also consumed alcohol. Alcohol doesn’t affect the way Narcan works.

However, Narcan won’t reverse the effects of alcohol. If you or someone else has overdosed on alcohol, call 911 or your local emergency number right away.

Narcan use in someone who is pregnant or breastfeeding

It’s not known whether Narcan is safe to use during pregnancy. Studies in animals didn’t find harmful effects when naloxone (the active drug in Narcan) was given to pregnant animals. However, animal studies don’t always reflect what will happen in humans.

If given to someone who’s pregnant, Narcan could cause side effects, such as opioid withdrawal symptoms, in a fetus. However, an opioid overdose can result in the death of the pregnant person or in pregnancy loss. Therefore, the American College of Obstetricians and Gynecologists recommends Narcan as an option for treating opioid overdose in someone who’s pregnant.

It’s not known if Narcan passes into breast milk or if it can cause side effects in a child who is breastfed. But because an opioid overdose can be fatal, Narcan can be used to save the life of someone who is breastfeeding if they’ve overdosed on opioids.

If you’ve received Narcan while pregnant or breastfeeding, contact your doctor right away. They can determine if you or your child need any extra monitoring or treatment.

If you have any questions about the safety of using Narcan in someone who’s pregnant or breastfeeding, talk with your doctor or pharmacist.

Narcan is used to treat a known or possible opioid overdose in an adult or child. This drug can be purchased from a pharmacy without a prescription.

You may have concerns about the possible side effects of using Narcan to treat opioid overdose.

Keep in mind that opioid overdose can be fatal, and Narcan can save someone’s life. And although Narcan may cause opioid withdrawal symptoms that can be unpleasant, for most people any side effects of Narcan are typically mild and temporary.

If you’re considering purchasing Narcan to keep with you in case of an opioid overdose, talk with your doctor or pharmacist about the drug’s possible side effects. Here are some questions to get you started:

• I have high blood pressure. Does that raise my risk for side effects from Narcan?
• Could my heart medications increase my risk for side effects from Narcan?

To learn more about Narcan, see these articles:

• All About Narcan Nasal Spray
• Dosage for Narcan: What You Need to Know
• Narcan and Cost: What You Need to Know

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