Promethazine dosage, forms, and strengths

Medically reviewed by Leslie Greenberg, MD
Board-Certified Family Physician
Updated Jul 23, 2024  •  Published Nov 14, 2023
Datos Verificados
In this article:

Promethazine is a generic prescription antihistamine primarily used to treat allergic reactions, nausea, vomiting, and motion sickness and to provide sedation in children or during medical procedures. Dosages vary depending on the condition. People with allergies typically take a single dose at bedtime but can alternatively take three smaller doses daily. Most people are usually given a single dose as a sedative but may require several doses before, during, and after a medical procedure. As an anti-nausea medication (antiemetic), promethazine is taken twice daily for motion sickness but can be taken four to six times daily for active nausea and vomiting. Although most people will take the generic version, healthcare providers may prescribe one of two brand-name versions: Phenergan, a promethazine injection, or Promethegan, a promethazine rectal suppository.

Promethazine forms and strengths

Promethazine comes in a variety of dosage forms and strengths, including:

  • Tablets: 12.5 milligrams (mg), 25 mg, 50 mg

  • Oral solution: 6.25 mg per 5 milliliters (mL)

  • Syrup: 6.25 mg/5 mL

  • Injection: 25 mg/mL, 50 mg/mL

  • Suppository: 12.5 mg, 25 mg

Promethazine dosage for adults

The Food and Drug Administration (FDA) has approved promethazine to treat allergic reactions, including seasonal allergies, rhinitis, allergic conjunctivitis, hives, and swelling (angioedema), as well as being used as a follow-on treatment for anaphylactic reactions after the acute symptoms have resolved. Promethazine is also used as a sedative and an anti-nausea medication. It can prevent motion sickness and nausea or treat nausea and vomiting, including nausea caused by medical procedures.

Check our best Promethazine prices

Promethazine dosage
Indication Starting dosage Standard dosage Maximum dosage
Allergy 25 mg taken once before bedtime OR 6.25–12.5 mg taken three times per day 25 mg taken once before bedtime OR 6.25–12.5 mg taken three times per day 50 mg/dose and 100 mg/day
Motion sickness 25 mg 30–60 minutes before traveling 25 mg twice per day  50 mg/dose and 100 mg/day
Nausea and vomiting 12.5–25 mg initial dose 12.5–25 mg doses every four to six hours 50 mg/dose and 100 mg/day
Prevention of nausea and vomiting during surgery and after 12.5–25 mg initial dose 12.5–25 mg doses every four to six hours 50 mg/dose and 100 mg/day
Sedation 25–50 mg  25–50 mg  100 mg/day
Sedation during labor 50 mg starting injection dose 25–75 mg injections  100 mg/day

Promethazine dosage for allergic reactions

As an antihistamine, promethazine, in all its forms, is primarily used to treat allergic reactions. Doses will vary, but the standard dose is 25 mg at bedtime.

  • Standard adult dosage for allergic reactions: 25 mg taken at bedtime OR 6.25–12.5 mg taken three times per day

Promethazine dosage for motion sickness

Promethazine has antiemetic properties, preventing nausea and vomiting due to motion sickness. As with other motion sickness drugs like Dramamine (diphenhydramine), most people only need to take a single dose before traveling. People traveling much of the day will take a second promethazine dose later. If someone is also traveling the next day, the suggested dosage is 25 mg when first waking up and another 25 mg before the evening meal.

  • Standard adult dosage for motion sickness: 25 mg 30–60 minutes before traveling and another 25 mg eight to 12 hours later if necessary

Promethazine dosage for nausea and vomiting

Most people will be given a 25 mg dose for nausea and vomiting. However, a smaller dose may be used.

  • Standard adult dosage for nausea and vomiting: 12.5–25 mg every four to six hours

Promethazine dosage for sedation

As with other antihistamines, promethazine causes drowsiness and sleepiness. It doesn’t put people to sleep but can relieve tension to help sleep soundly the night before a medical procedure. People who are asleep can be easily awakened but may be drowsy.

  • Standard adult dosage for sedation: 25–50 mg the night before a procedure or 25–50 mg immediately before or after a medical procedure

Promethazine dosage for labor

Pregnant women can take promethazine tablets before and after labor and before any other medical procedure using the dosage recommendations above. During labor, obstetricians may use promethazine injections to causesedation and to provide some pain relief. The average dose is 50 mg.

  • Standard adult dosage for obstetrics: 25–75 mg intramuscular or intravenous injection when active labor occurs—doses can be repeated at four-hour intervals up to a maximum dose of 100 mg in 24 hours

Promethazine dosage for children

Promethazine is FDA approved for use in children as young as two years of age for allergic reactions, motion sickness, nausea, vomiting, bedtime sedation, and sedation during a medical procedure. In addition to tablets, children can take promethazine oral solution or syrup for easier dosing. 

Allergic reactions

  • Standard promethazine dosage for allergic reactions in children ages 2 to 4 years old: 5–15 mg taken orally at bedtime OR 5 mg taken orally twice per day

  • Standard promethazine dosage for allergic reactions in children ages 5 to 9 years old: 10–25 mg taken orally at bedtime OR 5–10 mg taken orally twice per day

  • Standard promethazine dosage for allergic reactions in children ages 10 and older: 25 mg taken orally at bedtime OR 6.25–12.5 mg taken orally three times per day

  • Maximum promethazine dosage for allergic reactions in children ages 2 and older: 50 mg/day

Motion sickness

  • Standard promethazine dosage for motion sickness in children ages 2 and older: 12.5–25 mg taken twice per day, 30–60 minutes before travel and eight to 12 hours later if necessary 

Nighttime sedation

  • Standard promethazine dosage for nighttime sedation in children ages 2 and older: 12.5–25 mg taken at bedtime OR 0.5 mg per pound of body weight taken at bedtime

  • Standard promethazine dosage for preoperative sedation in children ages 2 and older: 0.5 mg per pound of body weight

  • Standard promethazine dosage for postoperative sedation in children ages 2 and older: 12.5–25 mg OR 0.5 mg per pound of body weight

  • Maximum promethazine dosage for sedation in children ages 2 and older: 25 mg/dose

Nausea and vomiting

  • Standard promethazine dosage for nausea and vomiting in children ages 2 and older: 0.5 mg per pound of body weight per dose every four to six hours

  • Maximum promethazine dosage for nausea and vomiting in children ages 2 and older: 25 mg/dose

Promethazine dosage restrictions

No dosage restrictions or reductions exist for people with kidney dysfunction, liver disease, or advancing age.

Promethazine is contraindicated in pediatric patients younger than two years old. The chance of respiratory depression in children younger than two years of age is serious enough that a black box warning has been added to the drug information sheet. Because of the risk of respiratory depression, promethazine should not be used in people in a coma or who have asthma, Reye’s syndrome, or sleep apnea.

Promethazine dosage for pets

Although promethazine can be used in animals, according to Plumb’s Veterinary Manual, promethazine is not commonly used in pets, and veterinarians have little experience with it. It’s usually used to prevent or treat nausea and vomiting. Dosages are not standardized. 

How to take promethazine

Like many oral medications, promethazine tablets, oral solution, and syrup are relatively easyto take. Rectal suppositories are placed in the rectum. A healthcare professional usually administers injections. 

  • Use this medicine as directed. A doctor or other healthcare professional will tell you how much medicine to use and provide additional medical advice.

Tablets

  • Store promethazine tablets at room temperature, protected from light, and in a childproof container. Keep out of reach of children.

Oral solution or syrup

  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup. Do not use kitchen measuring devices or tableware to measure out doses because they are not a standard size.

  • Store the oral solution or syrup at room temperature, away from light. Keep it out of the reach of children.

Rectal suppositories

  • For rectal suppositories, try to empty your bladder and bowel before inserting the suppository.

  • Remove the outer wrapper of the suppository before inserting it.

  • Do not handle the suppository for too long, or it will melt in your hand.

  • Lie down for a few minutes after the suppository has been inserted to give it time to melt.

  • Do not use the restroom after inserting the suppository.

  • Store the suppositories in the refrigerator. Do not freeze.

  • Take a missed dose of promethazine as soon as you remember it. If it is almost time for the next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

Promethazine dosage FAQs

How long does it take promethazine to work?

When taken orally, promethazine begins to have effects within 20 minutes. It doesn’t matter if it’s taken with food, but it may help avoid gastrointestinal upset.

How long does promethazine stay in your system?

The therapeutic effects of promethazine typically last four to six hours but can last up to 12 hours. With a half-life of seven to 14 hours, it normally takes one to two days to completely clear a dose from the body.

How long can you take promethazine?

Promethazine is generally intended for short-term use to treat allergic reactions, nausea, and vomiting and to provide sedation. There is no upper limit on how long it can be taken, but it should only be taken for as long as necessary.

How do I stop taking promethazine?

Promethazine does not cause physical dependence and can be stopped anytime without causing withdrawal symptoms. 

Can you overdose on promethazine?

Yes. A promethazine overdose can cause life-threatening adverse effects, including dangerously low blood pressure and respiratory depression. If too much promethazine is taken, common symptoms include extreme drowsiness, weakness, overactive reflexes, slowed breathing, weak breathing, unconsciousness, and seizures (rare). Get emergency medical attention if too much promethazine has been taken.

What interacts with promethazine?

Promethazine is a phenothiazine, a drug similar to early antipsychotic medications. Promethazine causes several changes in the nervous system, so it has many significant prescription drug interactions. The most significant is CNS depression. When combined with other central nervous system depressants such as opioids, benzodiazepines, barbiturates, or alcohol, its sedative side effects are amplified. It will also cause problems with drugs with similar effects as promethazine, like anticholinergic drugs, epinephrine, and MAO inhibitors (MAOIs). To avoid possible interactions, inform the healthcare provider of any prescription, over-the-counter medications, or supplements you are taking. Promethazine may also cause an unexpected and severe rise in ocular pressure in patients with a history of glaucoma.

Is it safe to take promethazine during pregnancy?

No clinical or animal studies have shown evidence of birth defects or pregnancy problems in women taking promethazine. The drug is sometimes used to provide sedation in women in labor. In those cases, there is no evidence that the drug affects labor or produces side effects in the newborn.

Is it safe to take promethazine while breastfeeding?

Short-term use of promethazine is considered safe while breastfeeding. However, promethazine may reduce breast milk quantity.

What are the side effects of promethazine?

Promethazine has several effects on the nervous system. It works as an antihistamine by blocking histamine, an anticholinergic drug, and an antidopaminergic drug. It has side effects typical of all these drugs. Common side effects include drowsiness, constipation, dizziness, sleepiness, blurred vision, disorientation, dry mouth, rhinitis, and urinary retention. Serious side effects include respiratory depression, involuntary movements, slow or fast heart rate, jaundice (yellowing of the skin and eyes), and neuroleptic malignant syndrome, a severe side effect of dopamine-blocking drugs like antipsychotics or promethazine.

Sources

Medically reviewed by Leslie Greenberg, MD
Board-Certified Family Physician

Leslie Greenberg, MD, is a board-certified practicing family physician with more than 25 years of doctoring experience. She was a psychology major at Northwestern University near Chicago, then graduated with an MD from the University of Nevada School of Medicine. She completed her family medicine residency at St. Joseph Hospital in Wichita, Kansas. She has trained more than 350 family medicine resident-physicians, been in private practice, and delivered babies for 22 years.

... 

Medicamentos A-Z:

Ver todos
ABCDEFGHIJKLMNOPQRSTUVWXYZ