Promethazine Dosages: Your GoodRx Guide

Promethazine (Promethegan) is an antihistamine medication with many uses. This includes allergies, motion sickness, and nausea and vomiting. It’s also used to help with sleep or to make you feel drowsy before surgery.

In this guide, we’ll discuss the approved promethazine dosages for adults and children. But keep in mind that your healthcare provider may give you different directions for taking promethazine than what’s detailed below based on your personal health and medical history.

What dosage forms does promethazine come in?

Promethazine is available as an oral tablet, oral liquid, or rectal suppository.

The oral liquid, which comes either as a syrup or solution, may be a better option for children or adults who have trouble swallowing tablets. Make sure to use a dosing cup or syringe to measure the liquid. These are more accurate than a household teaspoon.

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The rectal suppositories are useful if you can’t swallow oral forms or if you’re actively vomiting.

Promethazine is also available as an injection, but this form is only given by a healthcare provider in a medical setting.

What’s the typical promethazine dosage for adults?

The recommended promethazine dosage varies based on your age and what you’re taking it for. Depending on your situation and preferences, you may take it by mouth or rectally. Here are the recommended promethazine dosages for adults.

Allergies

Allergies are a common condition where the immune system overreacts to substances that are usually harmless. Promethazine works by blocking a chemical called histamine in the body, which is why it’s called an “antihistamine.” Histamine triggers your immune system and causes allergy symptoms, such as watery eyes or a runny nose. Blocking it helps treat those symptoms.

The typical promethazine dosage for adults with allergies is 25 mg once daily at bedtime. This is because promethazine can make you very drowsy after you take it.

An alternative promethazine dosage for allergies is 6.25 mg to 12.5 mg up to 3 times a day. But be aware that you may feel drowsy. Use caution when driving or doing other activities that require you to be alert.

After your initial allergy symptoms go away, your healthcare provider may lower your dose. It’s recommended to take the lowest effective dose possible. 

Motion sickness

Motion sickness causes nausea or dizziness related to motion or travel. It can also sometimes lead to vomiting.

The average promethazine dosage for adults with motion sickness is 25 mg two times daily. You’ll take the first dose of promethazine 30 to 60 minutes before travel. Then repeat the dose 8 to 12 hours later if necessary. After that, it’s sometimes recommended to take 25 mg in the morning and before the evening meal on each additional day of travel.

Nausea and vomiting

One of the more common uses of promethazine is for nausea and vomiting. This is often related to surgery.

The recommended promethazine dosage for adults with nausea or vomiting is 25 mg. After the first dose, another 12.5 mg to 25 mg can be taken every 4 to 6 hours as needed.

To prevent nausea and vomiting after surgery, the recommended promethazine dosage is 25 mg every 4 to 6 hours as needed.

Sedation

Promethazine is sometimes used to help you relax or sleep, in particular the night before a surgical procedure.

The typical promethazine dosage for restful sleep before surgery is 25 mg to 50 mg at bedtime.

Before or after an operation

You may also take promethazine for sedation and to help with nausea or pain related to a surgery or procedure.

The recommended promethazine dosage for adults before surgery is 50 mg. After surgery, the typical promethazine dosage is 25 mg to 50 mg.

What’s the typical promethazine dosage for children?

Below are the recommended promethazine dosages for children aged 2 years and older. Like adults, kids usually take promethazine by mouth or rectally.

Children under the age of 2 shouldn’t take promethazine for any reason. That’s because promethazine can cause serious breathing problems in young children. The FDA issued a boxed warning (the most serious type of medication warning) to alert people of this risk.

Allergies

The recommended promethazine dosage for children with allergies is 25 mg before bed. An alternative dosage is 6.25 mg to 12.5 mg 3 times a day. This is the same dosage as adults. It’s recommended to take the smallest effective dose possible.

Motion sickness

For children with motion sickness, the recommended promethazine dosage is 12.5 mg to 25 mg twice a day.

Nausea and vomiting

Your child’s healthcare provider will help determine the right promethazine dose for your child based on their body weight. The recommended promethazine dosage for nausea and vomiting in children is 0.5 mg per pound of body weight. The dose can be repeated every 4 to 6 hours as needed.

Sedation

For children, the recommended promethazine dosage for sedation is 12.5 mg to 25 mg at bedtime.

Before or after an operation

It’s possible your child’s healthcare provider will use promethazine to make your child feel drowsy before surgery. It can also help prevent nausea or pain after the surgery is over.

Your child’s healthcare provider will determine the dose for your child based on their body weight. The typical promethazine dosage for children before surgery is 0.5 mg per pound of body weight. After surgery, the typical promethazine dosage is 12.5 mg to 25 mg.

What happens if you miss a dose of promethazine?

If you miss a dose of promethazine, you’ll likely notice your symptoms return. It’s fine to take your dose as soon as you remember if you still need it. But if it's almost time for your next dose, skip the missed dose and take the next dose as scheduled. Don't double your dose to make up for the one you missed.

Contact your healthcare provider if you miss taking a promethazine dose before a surgical procedure. This could affect the timing of your procedure or the other medications you’re given beforehand.

What should you do if you take too much promethazine?

If you or your child accidentally take an extra dose of promethazine, don't panic. It’s unlikely to cause you harm. You may notice more side effects, like drowsiness or confusion. Be aware that children or people 65 and over may have opposite symptoms and feel stimulated or overexcited. It's best to let your healthcare provider know if you take an extra dose of promethazine and notice more or different symptoms than usual. They can help you manage them safely.

If a child or adult takes a large amount of promethazine, more serious side effects can happen. These include difficulty breathing, loss of consciousness, or even death. If you or your child take a large amount of promethazine, seek emergency care. You can also call Poison Control at 1-800-222-1222.

How to save on promethazine

There are many ways to save on promethazine, which is available as a lower-cost generic medication. GoodRx can help you save over 80% off the average retail price of the generic version. Generic promethazine’s price at certain pharmacies is as low as $9.99 with a free GoodRx discount.

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Written by:

Justin DeFlorian, PharmD, BCPS

Justin DeFlorian, PharmD, BCPS, is a board-certified clinical pharmacist. He received his Doctor of Pharmacy degree from the University of Wisconsin-Madison.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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