Narcan is a prescription brand-name medication. It’s approved by the Food and Drug Administration (FDA) to treat opioid overdose in both adults and children of all ages.

Narcan is a short-term emergency treatment. The drug is used in people who have taken or are thought to have taken more opioids than their body is able to process.

Here are some fast facts on Narcan:

  • Active ingredient: naloxone
  • Drug class: opioid antagonists
  • Drug form: single-use nasal spray

Like other drugs, Narcan can cause side effects. Read on to learn about potential common, mild, and serious side effects, as well as warnings. For a general overview of Narcan, see this article.

Narcan can cause certain side effects, some of which are more common than others. These side effects are usually temporary, lasting a few days or weeks after the drug is given. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Narcan in clinical trials:

* To learn more about this side effect, see the “Side effect specifics” section below.

Mild side effects can occur with Narcan use. This list doesn’t include all possible mild side effects reported with the drug. For more information, you can refer to Narcan’s patient information.

Mild side effects of Narcan can include:

These side effects are usually temporary, lasting a few days or weeks. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking Narcan and want to tell the FDA about it, visit MedWatch.

* To learn more about this side effect, see the “Side effect specifics” section below.

In rare cases, Narcan may cause serious side effects, which are sometimes called adverse effects. The list below may not include all possible reported serious side effects of the drug. For more information, you can refer to Narcan’s patient information.

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

Serious side effects* and their symptoms can include:

* To learn more about the side effects in this list, see the “Side effect specifics” section below.
† An allergic reaction is possible after using Narcan. But this side effect wasn’t reported in clinical studies.

Children younger than age 4 weeks are more likely to have life-threatening opioid withdrawal symptoms after receiving Narcan than older children or adults.

Serious symptoms of opioid withdrawal in children younger than age 4 weeks can include:

  • crying more often than usual
  • increased reflexes
  • seizures

If a child younger than age 4 weeks is given Narcan, call 911 or your local emergency number right away after the first dose. The child will need to be treated and monitored by emergency medical personnel as soon as possible after receiving the drug.

Narcan may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

How long does Narcan stay in your system?

Narcan can stay in your system for a couple of hours after your last dose.

Long-acting opioid drugs can stay in your body a lot longer than Narcan. For this reason, you may require additional doses of Narcan when the level of it in your system becomes too low.

If you have questions about how long Narcan may remain in your body, talk with your doctor.

Does Narcan have any interactions with other drugs?

There aren’t any drugs that are known to interact with Narcan. Because Narcan stays in your body for a very short period of time, it isn’t likely to interact with other medications.

However, you should always talk with your doctor or pharmacist about any other medications you’re taking before you use Narcan. They can help avoid any potential interactions that might occur between Narcan and other drugs you take.

What happens if you give Narcan to someone who doesn’t need it?

There aren’t any known safety issues with giving a person Narcan when they don’t need it. Narcan doesn’t have an effect on a person who’s sober from opioids. (“Sober” means they don’t have any opioids in their system.)

If you suspect, but aren’t certain, that a person has overdosed on opioids, you should still give them a dose of Narcan. This is because opioid overdose may, in some cases, be fatal if it isn’t treated. In this situation, it’s best to go ahead and give Narcan to this person just in case.

If you have more questions about giving Narcan to someone, talk with your doctor or pharmacist.

Are there any contraindications to using Narcan?

There’s only one known contraindication to using Narcan. A contraindication is a condition or factor that would prevent you from taking the drug.

You shouldn’t use Narcan if you’ve previously had an allergic reaction to naloxone (the active drug ingredient in Narcan). Using Narcan in this situation can cause serious side effects. For more information, see “Allergic reaction” in the “Side effect specifics” section below.

How long can I expect Narcan side effects to last?

Most side effects from Narcan go away within a few hours or days after taking the drug. Narcan is broken down and cleared from your body very quickly, so you aren’t likely to have long-term side effects from the drug.

For more information on how long Narcan side effects may last for you, talk with your doctor.

Does Narcan come in other forms besides a nasal spray?

Narcan itself is only available as a nasal spray. But naloxone (the active drug ingredient in Narcan) comes in another form: an injection (shot) that’s given in a hospital or clinic. The injection may be intravenous, intramuscular, or subcutaneous.

Narcan nasal spray and naloxone injections have similar side effects. But naloxone injections can cause more severe opioid withdrawal symptoms. This is because naloxone injections can produce higher levels of the drug in your body than Narcan.

If you have questions about the form of naloxone that’s best for you, talk with your doctor.

Learn more about some of the side effects that Narcan may cause.

Headache

Narcan may cause headache. This was a common side effect in clinical studies of the drug.

What you can do

It isn’t known for sure how long headache might last after receiving Narcan. But because the drug is cleared quickly from your body, it’s likely that your headache will ease quickly as well.

If your headache doesn’t go away quickly, taking over-the-counter pain relievers such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil) might help.

If your headache is bothersome or doesn’t go away within a few days, talk with your doctor. They can suggest other ways to relieve this side effect.

Opioid withdrawal

Narcan use can cause symptoms of opioid withdrawal. It isn’t known whether this side effect was rare or common in clinical studies of the drug.

If your body is physically dependent on opioids, you’re very likely to experience this side effect. This is because Narcan works by counteracting the opioids that are in your system. And once the effect of the opioids is reversed, you’ll probably experience withdrawal. This may be referred to as an aftereffect.

Symptoms of opioid withdrawal can include:

You might experience opioid withdrawal multiple times after Narcan is given for an opioid overdose. This is because you may need to receive multiple doses of Narcan to counteract long-acting or high doses of opioids.

What you can do

It’s important for you or someone else to call 911 or your local emergency number after the first dose of Narcan is given. When emergency medical personnel arrive, they’ll monitor you for signs of opioid withdrawal. If you experience symptoms of opioid withdrawal, they’ll be able to treat your condition quickly.

Heart problems when used after surgery

If you have surgery, sometimes you’ll be given opioids for pain relief or as anesthesia. In rare cases, your body may not be able to process these, which can lead to symptoms of opioid overdose.

The use of Narcan in these cases to reverse the effects of opioids after surgery can cause serious heart problems, including:

What you can do

You’re more likely to experience this side effect if you have existing heart disease or other heart problems, such as a history of heart attack. Be sure to talk with your doctor about any heart conditions you have. They’ll decide whether it’s safe for you to receive Narcan.

Allergic reaction

As with most drugs, Narcan can cause an allergic reaction in some people. But this side effect wasn’t reported in clinical studies.

Symptoms can be mild or serious and can include:

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

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Narcan. But if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take Narcan. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Heart disease. Narcan can cause heart problems if the drug is used to reverse the effect of opioids after surgery. If you have existing heart disease or other heart problems, such as a history of heart attack, your risk for this side effect is even higher. If you have any heart conditions, talk with your doctor about whether it’s safe to use Narcan. (For more information on heart problems when Narcan is used after surgery, see the “Side effect specifics” section above.)

Allergic reaction. You shouldn’t take Narcan If you’ve ever had an allergic reaction to Narcan or any of its ingredients. Talk with your doctor about which other treatments are better choices for you.

Alcohol use with Narcan

Interactions between Narcan and alcohol weren’t reported in clinical studies of the drug.

Keep in mind that Narcan won’t reverse an alcohol overdose. The drug is approved to treat only opioid overdose. If you or someone you know is experiencing an alcohol overdose, call 911 or your local emergency number right away.

Pregnancy and breastfeeding while taking Narcan

The risks of using Narcan while pregnant or breastfeeding aren’t entirely known. Animal studies didn’t show any harm to offspring born to females that were given naloxone* during pregnancy. But what happens in animal studies may not happen in humans. Also, it isn’t known if Narcan can pass into breast milk during breastfeeding.

However, opioid overdose can, in some cases, be fatal if untreated. So the benefits of treating an opioid overdose during pregnancy or breastfeeding outweigh the risks.

Keep in mind that if you’re pregnant and have been given Narcan, the fetus may experience opioid withdrawal symptoms. For this reason, it’s important that you see a doctor right away if you’re given Narcan during pregnancy.

If you have questions about using Narcan while pregnant or breastfeeding, talk with your doctor about the benefits and risks of using the drug.

* Naloxone is the active drug ingredient in Narcan.

Side effects can occur while using Narcan. Most side effects are mild and go away within a few hours or days after the drug is given and don’t require medical attention. Talk with your doctor if you experience bothersome side effects that persist for more than a few days after using the drug.

If you’d like to learn more about Narcan, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from using the medication.

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.