Promethazine is a generic prescription medication used to treat many conditions. The drug is approved for use in certain adults and children with:

The drug is also used along with other medications for pain after surgery. It can also be used to achieve sedation (a state of relaxation) in certain cases, such as before surgery. Promethazine is typically used short term.

Promethazine, also called promethazine hydrochloride, comes as an oral tablet, oral syrup, and oral solution. Promethazine also comes in other forms, including an injectable form and a suppository. However, this article does not cover these forms. If you’d like to learn more about promethazine injectable or suppository side effects, talk with your doctor or pharmacist.

As with other drugs, promethazine can cause side effects. Read on to learn about its potential common, mild, and serious side effects. For a general overview of promethazine, including details about its uses, refer to this article. Your doctor can also tell you more about promethazine.

Promethazine can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, 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 in the prescribing information of promethazine oral tablet, oral syrup, and oral solution:

Mild side effects can occur with promethazine use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to promethazine’s prescribing information for the oral tablet, oral syrup, and oral solution.

Mild side effects that have been reported with promethazine include:

These side effects may be temporary, lasting a few days to weeks. However, 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 Promethazine and want to tell the FDA about it, visit MedWatch.

For more information about this side effect, see “Promethazine: Side effect specifics” below.

Promethazine may cause serious side effects. Though serious side effects weren’t common, they can occur. The list below may not include all possible serious side effects of the drug. For more information, you can refer to promethazine’s prescribing information for the oral tablet, oral syrup, and oral solution.

If you develop serious side effects while taking promethazine, 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 that have been reported and their symptoms include:

  • Seizure. Symptoms may include:
    • uncontrolled movements of the arms or legs
    • loss of consciousness
    • confusion
  • Extrapyramidal symptoms (a movement disorder caused by certain drugs). Symptoms may include:
    • uncontrolled movements, especially of the face
    • grinding of the teeth
  • Changes in blood cell levels, such as low platelets or white blood cells. Symptoms may include:
    • fever
    • bleeding or bruising more easily
    • nosebleeds
  • Hallucinations. Symptoms may include:
    • hearing voices that aren’t there
    • seeing objects or people that aren’t there
  • Angioedema (fluid buildup under the deep layers of skin). Symptoms may include:
    • swelling of the eyes or face
    • trouble breathing
  • Changes in blood pressure or heart rate. Symptoms may include:
    • dizziness
    • headache
    • blurry vision
  • Liver problems. Symptoms may include:
    • abdominal pain
    • nausea or vomiting
  • Neuroleptic malignant syndrome (a serious nervous system condition caused by certain drugs). Symptoms may include:
    • fever
    • changes in blood pressure
    • sweating
  • Respiratory depression (trouble breathing), especially in young children*
  • Severe allergic reaction.†

* Promethazine oral tablet, oral syrup, and oral solution have a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). To learn more, see the “Promethazine: Side effect specifics” section below.
† An allergic reaction is possible after taking promethazine. However, it’s not clear how often this can occur with promethazine oral tablet, oral syrup, or oral solution. To learn more, see the “Promethazine: Side effect specifics” section below.

In most cases, the promethazine side effects that occur in children are the same as those that occur in adults.

However, promethazine can cause respiratory depression (trouble breathing).* This risk is higher in children. Due to this risk, it’s not recommended for children younger than 2 years old to take promethazine.

If your child is age 2 years or older and takes promethazine, their doctor may recommend frequent monitoring for breathing problems.

Also, large doses of promethazine in children can cause severe side effects, such as hallucinations and convulsions. These may be life threatening.

If you have questions or concerns about side effects that may occur while your child is taking promethazine, talk with their doctor or pharmacist.

* Promethazine oral tablet, oral syrup, and oral solution have a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). To learn more, see the “Promethazine: Side effect specifics” section below.

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

What are the side effects of promethazine in older adults?

In most cases, side effects of promethazine in older adults (ages 65 years and older) are similar to those in younger people.

However, older adults may have an increased risk of side effects occurring. This is because older adults’ bodies may process promethazine slower than younger peoples’ bodies. This can cause a buildup of the drug in the body, which can increase the risk of side effects. For example, older adults may have a higher risk of confusion, dry mouth, and sleepiness.

Due to the increased risk of side effects in older adults, doctors typically recommend older adults start treatment with a low dose of promethazine. Then, the doctor will increase the dose as needed to treat their condition.

If you have questions about promethazine’s side effects in older adults, talk with your doctor or pharmacist.

Does promethazine cause stomach cramps?

No, promethazine wasn’t specifically reported* to cause stomach cramps or stomach pain. However, it’s possible for this medication to cause nausea or vomiting. Nausea and vomiting can lead to stomach cramps.

In rare cases, it’s possible for promethazine to cause liver problems, which can cause abdominal pain as well. (For more details, see the “Promethazine: Serious side effects” section above.)

If you experience stomach cramps while taking promethazine, talk with your doctor. They can help determine what may be causing your stomach cramps and the best ways to treat them.

* To learn more about the reported side effects of promethazine, see the prescribing information for the oral tablet, oral syrup, and oral solution.

Learn more about some of the side effects that promethazine may cause. To find out more about these side effects, see the prescribing information for promethazine oral tablet, oral syrup, and oral solution. You can also talk with your doctor or pharmacist.

Respiratory depression in young children

Young children have an increased risk of respiratory depression (trouble breathing) as a side effect from taking promethazine. Due to this, promethazine has a boxed warning for the risk of breathing problems in children younger than 2 years old.

A boxed warning is the most serious warning recommended by the Food and Drug Administration (FDA). The purpose of a boxed warning is to alert patients and doctors about the risks of taking a medication. It’s not clear how often this side effect occurs with promethazine oral tablet, oral syrup, or oral solution.

Breathing problems can occur in anyone taking promethazine. In some cases, breathing problems can be serious or even life threatening. However, they may be the most serious in children younger than 2 years old.

What you can do

Doctors typically won’t prescribe promethazine to children younger than 2 years old. If your child is age 2 years or older and takes promethazine, their doctor will prescribe the lowest dose for the shortest time possible.

If you or your child is taking promethazine, talk with the doctor about the risks of breathing problems. If you notice any trouble breathing, or slow, shallow breaths while taking promethazine, go to the hospital right away or call 911 or your local emergency number.

Nausea

Some people may experience nausea from taking promethazine. It’s not clear how often this side effect occurs with promethazine oral tablet, oral syrup, or oral solution.

What you can do

Sometimes, promethazine may be prescribed to treat nausea. So if you experience nausea while taking promethazine, talk with your doctor. They can help determine whether promethazine is working to treat your condition or whether the drug is causing nausea as a side effect.

In some cases, taking a medication along with food can help decrease nausea. Talk with your doctor or pharmacist about ways to manage nausea that you may experience from promethazine. They may be able to recommend antinausea medications or other treatment options for you.

Dry mouth

It’s possible to have dry mouth from taking promethazine. It’s unknown how often this side effect occurs with promethazine oral tablet, oral syrup, or oral solution.

What you can do

If you experience dry mouth while taking promethazine, talk with your doctor or pharmacist. They may be able to recommend ways to ease this side effect. For example, they may recommend using lozenges or mouthwash made to help ease dry mouth.

Insomnia

Some people may experience insomnia from taking promethazine. It’s not clear how often this side effect occurs with promethazine oral tablet, oral syrup, or oral solution.

Symptoms can include trouble falling asleep or staying asleep. They can also include waking up too early and being unable to fall back asleep.

What you can do

If you experience insomnia from taking promethazine, talk with your doctor or pharmacist. They can help recommend ways to treat your insomnia. For example, they may recommend taking an over-the-counter melatonin supplement to help you fall asleep or stay asleep.

Allergic reaction

As with most drugs, promethazine can cause an allergic reaction in some people. It’s unknown how often this side effect occurs with promethazine oral tablet, oral syrup, or oral solution.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • 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

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 promethazine.

However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Before you start taking promethazine, be sure to tell your doctor about any medical conditions that you have. They can help determine whether promethazine is safe for you to take.

Boxed warning: Breathing problems in young children

This drug has a boxed warning for a risk of respiratory depression (trouble breathing) in young children. This is a serious warning from the Food and Drug Administration (FDA). For details, see the “Promethazine: Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before you take promethazine. This drug may not be the right treatment option for you if you have certain medical conditions or other factors that affect your health. These are known as drug-condition or drug-factor interactions. The conditions and factors to consider include:

Glaucoma. It’s possible for promethazine to worsen the symptoms of glaucoma. So if you have glaucoma, tell your doctor before taking promethazine. They can help determine whether this medication is safe for you.

Liver problems. Tell your doctor about any liver problems that you have before taking promethazine. It’s possible for this medication to cause liver problems. And if you already have a liver problem, taking promethazine may make your condition worse. Your doctor may recommend more frequent monitoring of your liver while you’re taking promethazine.

Breathing conditions. If you have any breathing conditions, such as chronic obstructive pulmonary disorder (COPD) or asthma, tell your doctor before taking promethazine. This medication can cause respiratory depression.* So if you already have a breathing condition, taking promethazine may worsen your condition. Talk with your doctor to find out whether it may be safe for you to take promethazine based on your condition.

Seizures. If you’ve ever had a seizure, tell your doctor before taking promethazine. This medication may increase your risk of a seizure occurring. So if you’ve ever had a seizure, you may have an increased risk of seizures occurring while taking the drug. In this case, talk with your doctor to find out whether it may be safe for you to take promethazine.

Allergic reaction. If you’ve had an allergic reaction to promethazine or any of its ingredients, your doctor will likely not prescribe promethazine. Taking promethazine could cause you to have another allergic reaction. Ask your doctor what other medications may be better options for you.

Bladder problems. Tell your doctor if you have any bladder problems, including bladder blockage or benign prostatic hypertrophy. Promethazine may worsen symptoms of bladder conditions. So if you have these conditions, your doctor can help determine whether promethazine is safe for you.

Gastrointestinal problems. If you have any gastrointestinal problems, such as a stomach or digestive blockage, tell your doctor before taking promethazine. In some cases, promethazine may worsen certain gastrointestinal problems. Your doctor can help determine whether promethazine is right for you.

Low blood cell levels. Tell your doctor if you have low blood cell levels, such as low white blood cells or low platelet levels. Promethazine may cause low levels of these blood cells. And if you already have low blood cell levels, taking promethazine can lower them further. In this case, your doctor may recommend more frequent monitoring of your blood cell levels.

Heart problems. If you have any heart problems, tell your doctor before taking promethazine. This drug can cause changes in blood pressure or heart rate. So if you already have heart problems, taking promethazine may make your condition worse. In this case, your doctor can help determine whether promethazine is safe for you.

* Promethazine oral tablet, oral syrup, and oral solution have a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). To learn more, see the “Promethazine: Side effect specifics” section above.

Alcohol with promethazine

It’s not recommended to drink alcohol while you’re taking promethazine. Drinking alcohol while taking promethazine may increase the risk of side effects caused by the drug, alcohol, or both. This is because alcohol and promethazine can cause similar side effects, including:

  • sleepiness
  • blurry vision or double vision
  • dizziness
  • confusion
  • vomiting
  • nausea*

If you have questions or concerns about drinking alcohol while you’re taking promethazine, talk with your doctor or pharmacist.

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

Pregnancy and breastfeeding while taking promethazine

It’s not known whether it’s safe to take promethazine while pregnant or breastfeeding.

Animal studies show that promethazine may increase the risk of pregnancy loss. However, animal studies don’t always indicate what may happen in humans.

In addition, it’s not known whether promethazine may pass into breast milk or what effects the drug may have on a child who is breastfed.

If you’re pregnant, planning to become pregnant, or breastfeeding, talk with your doctor before taking promethazine. They can help determine whether the drug is safe for you. Or they can recommend a different treatment option for your condition.

Most side effects of promethazine are mild. However, it’s possible to experience serious side effects from this drug as well.

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

Referring to the following articles about promethazine can provide you with additional information:

  • More information about promethazine. For details about other aspects of promethazine, refer to this article.
  • Cost. If you’d like to learn about promethazine and cost, see this article.
  • A look at your condition. For details about allergies, see our asthma and allergies hub. Talk with your doctor if you have questions about the other conditions that promethazine is used to treat.

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 another 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.