Sounds like 'pro-meth-ah-zeen'

Key points about promethazine

  • Promethazine is an antihistamine used to treat and prevent allergies and motion sickness.
  • It belongs to groups of medicines called antihistamines.
  • This medicine is not suitable for children 6 years and under.
  • Promethazine is also called Phenergan or Allersoothe.
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Promethazine is an antihistamine with a number of uses:

  • To relieve allergic conditions, eg, hay fever and skin rashes.
  • To prevent nausea (feeling sick) or vomiting (being sick), including when caused by motion sickness. It works by blocking certain chemicals (histamines) in your brain that can cause nausea and vomiting.
  • To make you feel sleepy. It may be taken for a few days only to help promote sleep in adults with sleeping problems.  

Promethazine is available as an injection, a liquid or tablets (10 mg and 25 mg). In Aotearoa New Zealand, promethazine liquid and tablets can be bought from a pharmacy without a prescription, after consultation with a pharmacist. Read more about pharmacist-only medicines.

Promethazine is not suitable for children 6 years and under. This medicine must not be used for sedation of children (to make children sleep). It can cause severe breathing problems, restlessness, aggression and hallucinations. 

Promethazine tablets are available in 2 strengths: 10 mg and 25 mg. The dose of promethazine depends on its use. Your doctor or pharmacist will advise you on the best dose for you. The following is a guide for use of promethazine in adults only. 

  • Allergies: One to three 25 mg tablets taken as a single dose at night, or one to two 10 mg tablets taken 2 to 3 times daily. 
  • Motion sickness: 25 mg taken the night before travel and repeated after 6 to 8 hours on the following day if needed. 
  • Sedation: One to three 25 mg tablets taken as a single dose at night.

  • Water: Take promethazine with a glass of water.
  • Food: You can take it with or without food.
  • Missed dose: It isn't harmful if you miss a dose of promethazine. If you forget your dose, take it as soon as you remember. But if it's nearly time for your next dose, just take the next dose at the right time. Don't take double the dose.
  • Motion sickness: If you're taking promethazine to prevent travel sickness, it's usually recommended that you take the first dose at bedtime on the evening before you are due to travel. You can then take a further dose on the morning of your travel if needed. Promethazine causes drowsiness or sleepiness and isn't recommended if you need to stay alert, eg, if you're driving.

  • Are you pregnant or breastfeeding?
  • Do you have problems with your liver or kidneys?
  • Do you have a heart condition?
  • Do you have glaucoma (increased pressure in your eye)?
  • Do you have epilepsy?
  • Do you have problems passing urine (peeing) or prostate problems?
  • Are taking any other medicines? This includes any medicines you can buy without a prescription, as well as herbal and complementary medicines.

If you said yes to any of these questions, it’s important that you tell your doctor or pharmacist before you start promethazine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Here are some things to know when you're taking promethazine. Other things may be important as well, so ask your healthcare provider what you should know about.

  • Drowsiness: Promethazine can make you sleepy. If this happens be careful when driving or using tools until you know how this medicine affects you.
  • Alcohol: Limit drinking alcohol while you're taking promethazine. Alcohol can increase the risk of side effects such as drowsiness.
  • Other medicines: Promethazine interacts with some medicines, herbal supplements and rongoā Māori, so check with your doctor or pharmacist before starting promethazine and before starting any new products.
  • Sensitivity to sunlight: Protect yourself from the sun (with sunblock, a hat and long sleeves). Promethazine can make you more sensitive to the sun. Don't use sunbeds.

Like all medicines, promethazine can cause side effects, although not everyone gets them. Often side effects go away once your body gets used to the new medicine.

Side effects What should I do?
  • Drowsiness
  • Dizziness
  • Be careful when driving or using tools until you know how this medicine affects you.
  • These effects put you at risk of falls and injuries especially if you are an older person. Tell your doctor if you are concerned.
  • Don't drink alcohol.
  • Dry mouth 
  • Experiencing a dry mouth is common when taking promethazine.
  • Try sucking on ice chips or lollies, or drink small sips of water.
  • Read more about dry mouth.
  • Sudden changes in mood
  • Confusion
  • Tell your doctor.
  • Blurred vision or fast heart rate
  • Tell your doctor.
  • Constipation (hard poos)
  • Eat a high fibre diet that includes a lot of fruit, vegetables, brown bread and bran-based breakfast cereals.
  • Drink plenty of water.
  • Talk to your doctor if you have discomfort.
  • Read more about constipation.

Read more about
medicines and side effects and reporting a reaction that you think might be a side effect.

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Stephanie Yee, Pharmacist, Auckland

Last reviewed: