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Promethazine oral forms side effects: A detailed guide

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Promethazine oral forms are prescribed for certain allergies, motion sickness, and care related to surgery. Promethazine is in a group of drugs called phenothiazines. It may cause mild or serious side effects, including difficulty breathing, drowsiness, and nausea.
Medically reviewed by Alex Brewer, PharmD, MBA
Updated on February 22, 2023

Specifically, the Food and Drug Administration (FDA) has approved promethazine oral forms for use in adults and certain children for the following uses:

  • sedation (a state of relaxation or sleepiness) used in agitation or surgery
  • nausea and vomiting from surgery or anesthesia use
  • prevention and treatment of motion sickness
  • pain after surgery, given with meperidine or other pain relievers
  • allergies, including seasonal allergies and hives

This article describes possible side effects of promethazine oral forms. You’ll also find information on cost savings and coupon options for promethazine.

Promethazine oral forms are generic medications. They aren’t available in a brand-name version.

Promethazine also comes in injectable and suppository forms. However, these forms aren’t described in this article. To learn more about these forms, including suppository side effects, talk with your doctor. Other forms are useful when you’re too nauseous or unable to swallow an oral form.

You can explore this overview article to learn more about promethazine oral forms, including the drug’s uses, dosage, ways to save on cost, and more.

Boxed warning: Risk of breathing problems in young children

Promethazine has a boxed warning for the risk of breathing problems in young children. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).

For details, see the “Side effects of promethazine in detail” section below.

More common side effects of promethazine

Promethazine may cause mild or serious side effects. Below are some of the more common side effects in studies of this medication.

Commonly reported side effects of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet include:

  • drowsiness
  • blood pressure changes
  • breathing problems
  • unusual movements, such as muscle spasms or twitches
  • hives
  • confusion and loss of coordination

Mild side effects of promethazine

Promethazine may cause certain mild side effects. Most often, mild side effects are temporary and can be easily managed. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.

Mild side effects that occurred in studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet include:

  • drowsiness
  • insomnia (difficulty sleeping)
  • double vision or blurry vision
  • confusion and loss of coordination
  • faintness
  • euphoria (feeling extremely happy or excited)
  • nervousness
  • ringing in the ears
  • nausea and vomiting
  • dry mouth
  • sun sensitivity
  • sore, swollen, or discolored skin
  • blood pressure changes
  • unusual movements, such as muscle spasms or twitches
  • hives
  • mild allergic reaction*

* To learn more about this side effect, see the “Side effects of promethazine in detail” section below.

Promethazine oral forms may cause more mild side effects than those listed above. For details, see the prescribing information for promethazine oral solution, promethazine oral syrup, and promethazine oral tablet.

Serious side effects of promethazine

Promethazine may cause certain serious side effects. If you have any serious side effects from promethazine, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911, or a local emergency number, or go to the nearest emergency room.

After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with promethazine oral forms.

Serious side effects that occurred in studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet include:

  • breathing problems, such as slowed breathing, asthma, or stuffy nose
  • seizures
  • hallucinations
  • neuroleptic malignant syndrome, which can cause rigid muscles, very high fever, changes in mental state, fast breathing, and blood pressure changes
  • paradoxical (opposite to what’s expected) reaction, such as agitation or excitability
  • jaundice (yellowing of the skin or the whites of the eyes)
  • heart rate changes
  • risk for misuse
  • low blood cell levels*
  • uncontrolled movements, such as tremors, muscle spasms, cramps, or repetitive motions*
  • risk of breathing problems in young children*†
  • severe allergic reaction*

* To learn more about this side effect, see the “Side effects of promethazine in detail” section below.
Promethazine oral solution, promethazine oral syrup, and promethazine oral tablet have a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of promethazine in detail” section below.

Side effects of promethazine in children

Promethazine has a boxed warning for the risk of breathing problems in young children. Boxed warnings are serious warnings from the Food and Drug Administration (FDA). For more information about this boxed warning, see the “Side effects of promethazine in detail” section below. Due to this risk, doctors usually do not prescribe promethazine to children ages 2 years and younger.

In studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet, side effects of promethazine in children are similar to those reported in adults described above. This includes serious side effects such as:

* To learn more about this side effect, see the “Side effects of promethazine in detail” section below.

Uncontrolled movements were more likely in children who were dehydrated and very ill. (With dehydration, you have a low fluid level.) This side effect can make it harder to diagnose other childhood conditions, including:

The drug manufacturer suggests closely monitoring children if they take promethazine. For example, drowsiness or dizziness may cause harm if a child tries to ride a bike.

Talk with your child’s doctor about the risks and benefits of promethazine. They may recommend a different medication for your child.

Common questions about side effects of promethazine

Here are answers to some common questions about the side effects of promethazine oral forms. If you have other questions, talk with your doctor or pharmacist.

Are the side effects of promethazine DM cough syrup different than those of promethazine cough syrup?

Yes, they are. Promethazine DM contains two drugs: promethazine and dextromethorphan. But, promethazine cough syrup contains only one active drug: promethazine.

If your doctor prescribes cough syrup with promethazine and dextromethorphan, do not take more than the recommended dosage. And do not take plain promethazine cough syrup in addition. Some side effects of promethazine and dextromethorphan are similar, so they can be worse if you take both medications. These include:

  • drowsiness
  • nausea
  • nervousness
  • dizziness

Dextromethorphan carries a risk of misuse and dependence. Misuse is when medications are taken in a way other than how they were prescribed. Dependence is when your body needs a drug to function like usual. If you become dependent on a drug, you may experience unpleasant withdrawal symptoms when you stop taking it. Learn more about dextromethorphan misuse, dependence, and possible overdose symptoms in this article.

To avoid a higher risk of side effects, dependence, or overdose, take all medications the way your doctor prescribes. Talk with your doctor or pharmacist if you have any questions about how to take promethazine DM.

How do the side effects of promethazine oral syrup compare with those of promethazine with codeine oral syrup?

Promethazine and codeine are different drugs, so they have different side effects.

If your doctor prescribes cough syrup with promethazine and codeine, be sure to take the recommended dosage. And do not take plain promethazine cough syrup in addition. Some codeine and promethazine side effects are similar, so they can worsen if you take both medications. For example:

Other side effects are more likely with codeine, not promethazine. These include:

A mixture of promethazine and codeine carries the risk of misuse and dependence. (Misuse is when medications are taken in a way other than how they were prescribed.) If you become dependent on a drug, you may experience unpleasant withdrawal symptoms when you stop taking it. To learn more about codeine withdrawal, see this article. Studies also show that promethazine itself carries a risk of misuse.

Promethazine and codeine have a risk of breathing problems,* which are worse if taken with alcohol or other drugs. This combination can lead to overdose, including the following symptoms:

  • confusion
  • discolored fingernails and lips due to lack of blood flow
  • hallucinations
  • difficulty breathing
  • low blood pressure
  • loss of consciousness
  • coma

To avoid a higher risk of side effects or overdose, take your medication the way it was prescribed. And talk with your doctor or pharmacist about which medications interact with promethazine and codeine.

* Promethazine oral solution, promethazine oral syrup, and promethazine oral tablet have a boxed warning for this risk in young children. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of promethazine in detail” section below.

Does promethazine cause different side effects in older adults?

Maybe. Worse side effects in older adults (ages 65 and older) were not reported in studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet.

But, older adults are at higher risk for sedation (a state of relaxation or sleepiness) and confusion from any drug with those side effects. Due to this risk, some health professionals avoid prescribing anticholinergic drugs for older adults. The drug manufacturer recommends starting with a lower dose in older adults.

Confusion and sedation are two anticholinergic effects. Anticholinergic drugs, including promethazine, block a chemical in your brain called acetylcholine. In general, older adults are more likely to have anticholinergic side effects from drugs like promethazine. Other anticholinergic effects include:

  • dry mouth
  • blurred vision
  • difficulty urinating
  • constipation
  • memory problems

If you’d like to know more about the side effects of promethazine given your age, talk with your doctor.

Is constipation a side effect of promethazine?

It’s possible. Constipation was not reported in studies of promethazine. But, it has been reported since the drug was approved for use.

Many factors can lead to constipation, including diet, low fluid intake, and possibly other medications.

If you have constipation, there are several ways to treat it, including:

Promethazine is sometimes prescribed with codeine. Like other pain relievers, codeine can lead to constipation. Talk with your doctor about all medications you take and ask which ones may cause constipation.

If you have constipation, ask your doctor about ways to manage it.

Does promethazine cause long-term side effects?

Yes, it can. Long-term side effects could be side effects that start either while you’re taking promethazine or after you stop the drug.

If they occur, the following side effects typically happen while someone is taking promethazine. These side effects can lead to long-term effects.

  • Neuroleptic malignant syndrome (NMS). NMS is a rare side effect of promethazine. It’s possibly life threatening and requires prompt treatment. If left untreated, NMS can lead to long-term issues, such as blood clots, kidney failure, and even death. Symptoms of NMS include:
  • Leukopenia (low white blood cell level). Leukopenia is also a rare side effect of promethazine. White blood cells help your body fight infection. Having a low white blood cell level means you have a higher risk of infection. If you develop a serious infection such as pneumonia, it could have long-term effects on your breathing. Symptoms of leukopenia include:
    • mouth sores
    • fever
    • chills
    • draining pus from a wound or injury

Talk with your doctor about symptoms such as these to watch for while you’re taking promethazine. Most long-term effects can be avoided when side effects are identified early and treated promptly.

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Side effects of promethazine in detail

Below you’ll find details on some of the side effects of promethazine oral forms.

Risk of breathing problems in young children

Promethazine has a boxed warning for the risk of breathing problems in young children. Boxed warnings are serious warnings from the Food and Drug Administration (FDA). In some reports of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet, these breathing problems led to death.

Due to this risk, doctors usually don’t prescribe promethazine to children ages 2 years and younger. If your child’s doctor prescribes promethazine, they’ll be especially careful to avoid other drugs that also cause breathing problems. Children older than 2 years may take promethazine at dosages based on their weight.

Symptoms of breathing problems in children include:

  • fast breathing
  • change in breathing sounds, such as a whistling sound
  • higher heart rate
  • flaring nose
  • sweating

Ways to manage

If your child is having difficulty breathing, this is a medical emergency. Take them to the nearest emergency room right away and call their doctor. Or, you can call 911 or your local emergency number.

Talk with your child’s doctor about how to monitor your child for breathing problems.

Uncontrollable movements

Uncontrolled movements were side effects in studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet. These are also called extrapyramidal symptoms, and they can be mild or severe.

Examples include:

  • tremors
  • stiff muscles
  • muscle spasms or cramps
  • repetitive motions
  • twisting motions
  • changes in the way you walk

These movements involve different body parts, including:

  • tongue
  • neck
  • torso
  • legs or arms

Ways to manage

Uncontrolled movements may be a serious side effect of promethazine. They require prompt medical attention regardless of their severity.

Possible treatments include:

Talk with your doctor right away if you notice movement changes. Even if a treatment for uncontrolled movements is prescribed, your doctor will likely stop your promethazine treatment.

Low blood cell levels

Low levels of certain blood cells was a side effect in studies of promethazine. These included white blood cells and platelets. Most cases of this side effect occur when promethazine is used with other drugs that cause low blood cell levels.

Specifically, leukopenia and agranulocytosis were reported. These conditions refer to low levels of certain types of white blood cells. They can lead to an increased risk of infection.

Thrombocytopenia was also reported. With this condition, you have a low platelet level. It can lead to bleeding disorders.

Symptoms of low blood cell levels include:

If you already have low bone marrow function, you’re at higher risk of low blood cell levels with promethazine.

Ways to manage

Your doctor will monitor your blood cell levels while you take promethazine. If any of the levels are lower than expected, they’ll likely decrease your dosage or temporarily pause your treatment.

In rare, severe cases, you may need other treatments to manage blood cell levels. This is very unlikely when promethazine is used once, such as prior to surgery, or used on its own. But, if promethazine is used with other drugs that lower blood cell counts, your levels may drop to severely low levels requiring treatment. Examples of these may include:

Even though this side effect is rare, talk with your doctor about symptoms to watch out for. Also, ask your doctor whether you have health conditions that may increase your risk of this side effect.

Allergic reaction

For some people, promethazine oral forms can cause an allergic reaction. Allergic reactions were reported in studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet.

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

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

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening. If you’ve had a serious allergic reaction to promethazine oral forms, your doctor may recommend taking a different medication instead.

Warnings for promethazine

Below are some factors you may want to discuss with your doctor before taking promethazine oral forms.

Boxed warning: Risk of breathing problems in young children

Promethazine has a boxed warning for the risk of breathing problems in young children. Boxed warnings are serious warnings from the Food and Drug Administration (FDA).

For details, see the “Side effects of promethazine in detail” section above.

Other warnings

It may not be safe for you to take promethazine if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether promethazine is a safe treatment option for you.

Before taking promethazine oral forms, tell your doctor about your health and medications you take. Conditions and factors to consider include those listed below.

Anticholinergic effects. Promethazine is an anticholinergic drug, which means it blocks a chemical in your body called acetylcholine. This can cause problems if you have certain conditions. Examples include:

  • If you have a bladder blockage or enlarged prostate, promethazine may make it more difficult to urinate.
  • If you have certain types of glaucoma (too much pressure in your eye), promethazine could make it worse.
  • If you already take medication that causes dry mouth or constipation, promethazine could make it worse.
  • If part of your digestive system is narrowed because of an ulcer, promethazine can make a blockage more likely.

Activities that require alertness. Promethazine can impair your balance and concentration. It may not be safe to drive or do other things that require an alert mind while taking promethazine. Wait until you know how promethazine affects you. This risk of impairment can be worse if you take other medications that also cause confusion and sedation.

Bone marrow disease. If you have bone marrow disease or take medications that suppress your bone marrow function, promethazine could make it worse. A side effect of promethazine is low levels of certain blood cells, which are made in your bone marrow. For details, see the “Side effects of promethazine in detail” section above.

Liver problems. The liver is responsible for breaking down promethazine after you take a dose. If you have liver disease, your body might take longer to remove promethazine. You may be at higher risk of side effects from the drug.

Planned laboratory tests. Promethazine may interfere with accurate lab test results, including pregnancy tests and glucose tolerance tests. Talk with your doctor about this before having lab tests performed.

Heart problems. If you have heart disease, promethazine could make it worse. In the drug’s studies, heart rhythm changes was a side effect of promethazine.

Breathing problems. If you have breathing problems such as asthma or chronic obstructive pulmonary disorder COPD, promethazine could make your symptoms worse. It can thicken the mucus in your lungs. Slowed breathing is also a side effect of promethazine.

Sleep apnea. Sleep apnea is a condition in which you stop breathing temporarily while asleep. Promethazine could thicken mucus in your airways and make it harder to breathe.

Seizures. If you have seizures, promethazine could make them occur more often. Certain medications taken with promethazine may put you at higher risk of seizure. Talk with your doctor about all medications you take and whether any may increase your seizure risk.

Allergic reaction. If you’ve had an allergic reaction to promethazine or any of its ingredients, your doctor will likely not prescribe this medication. Ask them about other treatment options that may be better for you.

Promethazine and pregnancy

It’s not known if promethazine is safe to take during pregnancy. There aren’t enough studies on promethazine when taken during pregnancy.

That said, it may be prescribed as a treatment for nausea and vomiting during pregnancy. The American College of Obstetricians and Gynecologists suggests promethazine for this use if you and your doctor agree that the benefits outweigh the risks.

Talk with your doctor if you’re pregnant or planning to become pregnant. They’ll discuss the potential risks and benefits of taking promethazine during pregnancy.

Promethazine and breastfeeding

In the drug’s studies of promethazine oral solution, promethazine oral syrup, and promethazine oral tablet, it’s not known if the promethazine passes into breast milk. But, due to the risk of serious side effects occurring in a child who is breastfed, breastfeeding while taking promethazine is not recommended.

Talk with your doctor if you’re breastfeeding or planning to breastfeed. They can discuss the benefits and risks of stopping breastfeeding or stopping treatment with promethazine.

Promethazine and alcohol

Promethazine oral forms are known to interact with alcohol.

Promethazine and alcohol both cause drowsiness as a side effect. If taken together, the drowsiness can worsen.

If you drink alcohol, talk with your doctor about whether it’s safe to consume it during your treatment with promethazine.

What to ask your doctor

This article describes common and serious side effects of promethazine oral forms. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about treatment with this medication.

Here’s a list of some possible questions you may want to ask your doctor:

  • Am I more likely to have promethazine side effects if I also take an antidepressant?
  • Will a lower dose of promethazine be less likely to cause side effects?
  • How long will promethazine side effects last if I take it for surgery?
  • Do I have a risk of high blood pressure if I take promethazine?

Disclaimer: Optum Perks 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.

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