Promethazine (Phenergan)

Promethazine (Phenergan)-Other brand names: Avomine, Sominex

On this page

  1. About promethazine
  2. Key facts
  3. Who can and cannot take promethazine
  4. How and when to take promethazine
  5. Side effects
  6. How to cope with side effects of promethazine
  7. Pregnancy and breastfeeding
  8. Cautions with other medicines
  9. Common questions about promethazine

1. About promethazine

Promethazine (Phenergan) Promethazine is an antihistamine medicine that relieves the symptoms of allergies.

It’s known as a drowsy (sedating) antihistamine, so it’s more likely to make you feel sleepy than other antihistamines.

Promethazine is used for:

  • short-term sleep problems (insomnia) – including when a cough, cold or itching is keeping you awake at night
  • allergies, including hay fever and hives (urticaria)
  • feeling and being sick (vomiting) – due to motion sickness or vertigo
  • cold symptoms, such as coughing and a runny nose

You can buy promethazine from pharmacies, where it’s often sold as Avomine, Phenergan or Sominex. Promethazine is also available on prescription.

It comes as tablets, capsules and a liquid that you swallow.

You can also buy promethazine mixed with other medicines, such as paracetamol, dextromethorphan, pholcodine or pseudoephedrine, to treat coughs and colds or pain.

2. Key facts

  • Do not drink alcohol while taking promethazine. Alcohol increases the risks of side effects.
  • To help you sleep, take promethazine 20 minutes before you go to bed. It normally takes about 30 minutes to work.
  • To prevent motion sickness, take promethazine the night before a long journey or 1 to 2 hours before a short journey.
  • Common side effects of promethazine include drowsiness, headaches, nightmares and feeling dizzy, restless or confused.
  • When promethazine is mixed with other medicines, it’s also known by the brand names Day & Night Nurse, Fedril and Night Nurse.

3. Who can and cannot take promethazine

Promethazine can be taken by most adults.

Children under 6 should not be given cough and cold medicines containing promethazine if they have been bought at a pharmacy. These medicines should only be given if prescribed by a doctor.

Some types of promethazine medicines are not suitable for children over 6. Some are labelled 12+ and some are labelled 16+. Your doctor or pharmacist will advise which are the safest for children.

Promethazine is not suitable for some adults. To make sure it’s safe for you, tell your doctor or pharmacist if you:

  • have ever had an allergic reaction to promethazine or any other medicine
  • have an eye problem called primary angle closure glaucoma
  • have problems peeing or emptying your bladder
  • have epilepsy or any other health problem that causes seizures or fits
  • are due to have an allergy test. Promethazine can affect your results, so you may need to stop taking it a few days before your test. Ask the clinic where you are due to have your allergy test
  • are unable to have any alcohol – some liquid promethazine products contain a very small amount of alcohol, so check the ingredients and the packaging carefully
  • are trying to get pregnant. Promethazine can affect home pregnancy tests. If you think you’re pregnant, speak to your doctor so they can arrange a blood test instead

4. How and when to take promethazine

If you or your child have been prescribed promethazine, follow your doctor’s instructions about how and when to take it.

Only take promethazine when you need it – for example, if you’re unable to sleep because you’re worrying about something or your cold symptoms are keeping you awake.


If you have bought promethazine or any medicine containing promethazine from a pharmacy, follow the instructions that come with it, or ask a pharmacist for advice.

Dosage and strength

Promethazine comes in 10mg, 20mg and 25mg tablets. Your dose depends on why you’re taking it:

  • short-term insomnia – you’ll usually take 20mg to 50mg at night
  • hay fever – you’ll usually take from 10mg twice a day to 20mg, 3 times a day
  • hives – you’ll usually take from 10mg twice a day to 20mg 3 times a day
  • preventing motion sickness – you’ll usually take 25mg 1 to 2 hours before a short journey or 25mg the night before a long journey
  • treating motion sickness – take 25mg as soon as possible and 25mg the same evening, followed by 25mg the following evening (if you need it)
  • vertigo – the dose can vary from 25mg a day to 25mg 4 times a day

If you’re taking liquid which contains 5mg of promethazine in 5ml, follow the instructions that come with the medicine for how much to take.

Doses are lower for children. Your doctor will use your child’s age to work out the right dose.

Promethazine mixed with other medicines

Promethazine can come mixed with other medicines, such as paracetamol. This is usually used to treat cough and cold symptoms. Your dose will depend on the type of medicine you’re taking.

Check the instructions on the packaging carefully, or ask your pharmacist or doctor if you’re unsure.

How to take it

You can take promethazine tablets, capsules and liquid with or without food.

How to take tablets and capsules

Always take your promethazine tablets or capsules with a drink of water. Swallow them whole. Do not chew them.

How to take liquid

Liquid medicines containing promethazine come with a plastic syringe or spoon to help you measure out the right dose.

If you do not have a syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as you will not get the right amount.

What if I forget to take it?

For motion sickness, take it as soon as you remember.

For anything else, skip the missed dose and take your next dose at the usual time.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you often forget doses, it may help to set an alarm to remind you. You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.

What if I take too much?

Too much promethazine can be dangerous.Promethazine (Phenergan)

If you take more than your usual dose, you may:

  • feel very sleepy
  • have a very fast, irregular or pounding heartbeat (palpitations)
  • have breathing problems

In serious cases, you can become unconscious or have seizures or fits and may need emergency treatment in hospital.

If your child takes too much promethazine, they may also:

  • move unsteadily or stumble
  • have uncontrolled movements, especially in their hands or feet
  • see or hear things that are not there (hallucinations)
  • have an irregular heartbeat

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