9 Promethazine Side Effects You Should Know About

Promethazine is a medication that has many uses. Most often, it’s used for nausea and vomiting from cancer treatment (chemotherapy), surgery, and motion sickness. It can also be used to help people sleep before or after surgery, for allergies, and allergic skin reactions.

Promethazine is available as a tablet, oral liquid, and rectal suppository (Promethegan). It’s also available as an injection. Like all medications, promethazine has side effects. And if you’re taking this medication, it’s important to know what to watch out for.

Below, we’ll discuss nine promethazine side effects you should know about.

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1. Drowsiness

Promethazine has many effects on the body. It blocks multiple chemicals, including dopamine, histamine, and acetylcholine.

Medications that block histamine (antihistamines) and acetylcholine (anticholinergics) can cause drowsiness. This is one of the most common side effects of promethazine. In fact, promethazine is sometimes used before or after surgeries to help you sleep.

Depending on why you’re taking promethazine, you may only need one dose a day. If this is the case, try taking your dose at night to avoid daytime sleepiness.

But if you need multiple daily doses and drowsiness is affecting you, talk to your healthcare provider. You may need a lower dose or another medication altogether. But don’t make any changes without talking to your provider first.

When starting promethazine, avoid activities that require alertness until you see how it affects you. This includes driving. And you should try to avoid other medications and substances that can worsen drowsiness. This includes opioids, benzodiazepines, and alcohol.

2. Dizziness

Medications with anticholinergic properties can also cause dizziness.

If promethazine is causing dizziness, there are a few things you can try to lessen this side effect. This includes taking your time when moving from one position to another (like sitting to standing). And whenever you feel dizzy, find a place to sit or lie down.

Like drowsiness, certain medications and substances can make dizziness worse. Examples of medications that can make dizziness worse include blood pressure medications, antidepressants, and antiepileptics.

Alcohol can also worsen dizziness. Talk to your healthcare provider or pharmacist about whether any medications you take can cause or worsen dizziness.

If you’re over 65 years old, ask your healthcare provider if promethazine is still a safe option. The drowsiness and dizziness it can cause can make it more likely to fall while taking it. Falls are the leading cause of injury in older adults.

3. Confusion

Promethazine can cause some people to feel confused and disoriented. Like drowsiness and dizziness, this may affect your physical ability to do tasks like driving. It may also affect your ability to think clearly or focus on a task.

Many medications and substances that can worsen drowsiness and dizziness can worsen confusion. This includes opioids, benzodiazepines, and some antidepressants.

Confusion can also be worsened by alcohol. Ask your pharmacist to check if any medications you take could worsen confusion from promethazine.

If you experience confusion, let your provider know. They may help you lower your dose or switch you to another medication.

4. Ringing in your ears

Promethazine is one of several medications that can cause ringing in your ears (tinnitus). The good news is that most of the time, tinnitus caused by medicines goes away when the medication is stopped.

If you experience ringing in your ears, talk to your healthcare provider. They will perform an exam to make sure there is nothing else going on. If they find out that promethazine is causing tinnitus, they will recommend another medication.

Although there are many prescription and over-the-counter (OTC) products reported to relieve tinnitus, many of these products haven’t been shown to work. Some prescription medications may work for some people, but they’re used off-label.

5. Blurry vision

Promethazine can cause blurry vision. This is another side effect that’s caused by its anticholinergic properties.

If you have any changes in your eyesight, talk to your healthcare provider. They’ll want to check whether something else could be causing vision problems. If your blurry vision is caused by promethazine, your provider may switch you to another medication if needed.

6. Dry mouth

Dry mouth can happen due to promethazine’s anticholinergic and antihistaminergic effects. It can be a bothersome side effect, but there's a few things you can try to find relief.

These include:

• Drinking cool liquids throughout the day or suck on ice chips

• Chewing sugar free gum or suck on sugar-free hard candy

• Trying an OTC saliva substitute, like Biotene or BioXtra

• Practicing good oral care (like brushing and flossing twice a day) to lower your risk of dental problems

If these at home remedies don't work, talk to your healthcare provider. They may recommend stopping promethazine or trying a prescription medication for dry mouth.

7. Trouble breathing in young kids

Promethazine has a boxed warning for trouble breathing in kids less than 2 years old. A boxed warning is the most serious warning the FDA can assign a medication.

For this reason, promethazine shouldn’t be used in children under 2 years old. Other people with certain medical conditions that affect breathing should also be careful when using promethazine.

This also includes people with sleep apnea or chronic obstructive pulmonary disease (COPD). And if you take medications that can affect breathing, like opioids and benzodiazepines, you should also be more cautious.

Before starting promethazine, talk to your healthcare provider about whether it’s a safe option. Based on your medical history and other medications, they might recommend another medication.

8. Seizures

Though rare, promethazine can raise the likelihood of having a seizure. This is called “lowering the seizure threshold.”

If you have a history of seizures, promethazine may not be the best choice for you. This is also true if you take or take other medications that lower the seizure threshold. Some examples include bupropion (Wellbutrin XL, Wellbutrin SR), cyclobenzaprine (Amrix), and diphenhydramine (Benadryl).

Let your healthcare provider know if you have a history of seizures before starting promethazine. And make sure they know what other medications you take. They’ll help you weigh the risks and benefits of taking promethazine.

If you experience a seizure, let your healthcare provider know right away.

9. Movement problems

One possible side effect of promethazine is extrapyramidal symptoms (EPS). EPS refers to movement problems caused by medications that block dopamine, including promethazine. EPS includes a wide range of movement issues.

Some examples include:

• An inability to be still (akathisia)

• Uncontrollable muscle contractions (dystonia)

• Symptoms that look like Parkinson’s disease, including tremors (drug-induced parkinsonism) 

• Repetitive movements, usually of the face and mouth (tardive dyskinesia)

Often, managing EPS involves lowering the dose of promethazine or stopping it completely. In some cases, you may need another medication to help with movement problems. For example, medications like propranolol (Inderal LA) may help treat akathisia.

Let your healthcare provider know right away if you experience any movement problems.

*Keep in mind: Movement problems may also be a sign of another serious (but rare) promethazine side effect called neuroleptic malignant syndrome (NMS). With NMS, you may experience rigid muscles as a symptom. You may also have a fever, confusion, and extreme changes in heart rate, blood pressure, and breathing. These symptoms are severe and can be life-threatening. Get medical help immediately if you experience them.

When should I contact my healthcare provider about promethazine side effects?

Get emergency care if you experience trouble breathing or seizures. If you have movement problems, contact your provider immediately. These are more severe side effects of promethazine.

You may be able to manage mild promethazine side effects — like drowsiness, dizziness, or dry mouth — at home. But if they persist, it's a good idea to reach out to your provider. They may recommend lowering the dose or trying another medication.

Many other medications and substances can worsen side effects of promethazine. Give your provider and pharmacist a list of all the medications and supplements you take. They can help you check if anything you take interacts with promethazine.

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Written by:

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP

Nicole E. Cieri-Hutcherson, PharmD, BCPS, NCMP, has over a decade of experience as a pharmacist, professor, and researcher. She was a full-time clinical professor in the pharmacy practice department at D’Youville School of Pharmacy before subsequently joining the faculty of the pharmacy practice department at the University at Buffalo School of Pharmacy and Pharmaceutical Sciences.

Edited by:

Amy B. Gragnolati, PharmD, BCPS

Amy Gragnolati, PharmD, BCPS, is a pharmacy editor for GoodRx. Amy currently holds her pharmacist license in Georgia and California.

Reviewed by:

Tegan Smedley, PharmD, APh

Tegan Smedley, PharmD, APh, has 10 years of experience as a pharmacist. She has worked in a variety of settings, including retail, hospital, and ambulatory care.

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