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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 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 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 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.

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

Urgent advice: Contact 111 for advice if:

  • you take more than your usual dose of promethazine

Go to or call 111

If you need to go to A&E do not drive yourself. Get someone else to drive you or call for an ambulance.

Take the promethazine packet or leaflet inside it, plus any remaining medicine, with you.

5. Side effects

Common side effects

Like all medicines, promethazine can cause side effects, although not everyone gets them.

Talk to your pharmacist or doctor if these side effects bother you or do not go away:

  • feeling tired during the daytime
  • nightmares
  • feeling dizzy or unsteady on your feet, or having difficulty concentrating
  • headaches

Promethazine can sometimes make your skin more sensitive to sunlight. Keep out of direct or strong sunlight and follow sun safety advice.

If you're over 65, you're more likely to get side effects such as:

  • feeling confused
  • dry mouth
  • blurred vision
  • difficulty peeing

Talk to a doctor or call 111 straight away if you have these side effects.

Children are more likely to get side effects such as feeling restless or excited.

Serious side effects

Call your doctor straight away if:

  • the whites of your eyes or your skin turn yellow, although this may be less obvious on black or brown skin – these can be signs of liver problems
  • you notice more bruising or bleeding than normal
  • you have muscle stiffness or shaking, or unusual face or tongue movements

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to promethazine.

Immediate action required: Call 999 now if:
  • your lips, mouth, throat or tongue suddenly become swollen
  • you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
  • your throat feels tight or you're struggling to swallow
  • your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • you suddenly become very confused, drowsy or dizzy
  • someone faints and cannot be woken up
  • a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

These are not all the side effects of promethazine. For a full list, see the leaflet inside your medicine packet.


You can report any suspected side effect using the Yellow Card safety scheme.

Visit Yellow Card for further information.

6. How to cope with side effects of promethazine

What to do about:

  • feeling sleepy during the daytime – this usually wears off 12 hours after a dose. Do not drive, cycle or use tools or machinery if you're feeling this way.
  • nightmares – speak to your pharmacist or doctor if these do not go away or are troubling you.
  • feeling dizzy or unsteady on your feet, or having difficulty concentrating – stop what you're doing and sit or lie down until you feel better. If the feeling does not go away or is troubling you, do not take any more medicine and speak to a pharmacist or doctor.
  • headaches – make sure you rest and drink plenty of fluids. Talk to your doctor if the headaches last longer than a week or are severe.

7. Pregnancy and breastfeeding

Promethazine and pregnancy

Promethazine can be used in pregnancy. There is no good evidence that it is harmful to your baby, but it can have side effects such as drowsiness.

For the treatment of hay fever your doctor or pharmacist may recommend a non-drowsy antihistamine (loratadine).

Promethazine and breastfeeding

If your doctor or health visitor says your baby is healthy, promethazine can be used during breastfeeding. If you are prescribed promethazine, it's better to take occasional doses or only for a short time.

It's not known how much promethazine passes into breast milk but it is likely to be a small amount. It has been used for many years without causing babies to have side effects. However, promethazine is a drowsy antihistamine, so may also make your baby sleepy too. It may also reduce the amount of milk you produce.

If you're breastfeeding or planning to breastfeed, talk to your doctor or pharmacist, as other medicines might be better while you're breastfeeding.

If your baby is not feeding as well as usual, seems unusually sleepy, or seems irritable, or if you have any other concerns about your baby, talk to your doctor, pharmacist, health visitor or midwife.

Non-urgent advice: Tell your doctor if you're:

  • trying to get pregnant
  • pregnant
  • breastfeeding

Find out more about how promethazine can affect you and your baby during pregnancy on the Best Use of Medicines in Pregnancy (BUMPs) website.

8. Cautions with other medicines

Some medicines and promethazine can affect each other and increase the chance of having side effects.

Tell your pharmacist or doctor if you're taking:

  • a type of antidepressant called a monoamine oxidase inhibitor, such as phenelzine
  • a type of painkiller called an opioid, such as codeine, morphine or oxycodone
  • any medicine that makes you drowsy, gives you a dry mouth, or makes it difficult for you to pee – taking promethazine might make these side effects worse

If you're taking a cough or cold remedy or a painkiller containing promethazine, check carefully what the other ingredients are.

For example, promethazine often comes mixed with paracetamol. If you take 2 medicines that both contain paracetamol, there's a risk of overdose.

Ask your pharmacist for advice before you take this medicine together with any other painkillers or medicines.

Mixing promethazine with herbal remedies and supplements

There might be a problem taking some herbal remedies and supplements alongside promethazine, especially ones that cause side effects such as sleepiness, a dry mouth or making it difficult to pee.

Ask your pharmacist for advice.

Important: Medicine safety

Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.

9. Common questions about promethazine

How does promethazine work?

Promethazine is a medicine called an antihistamine. It's classed as a drowsy (sedating) antihistamine.

When you come into contact with something you're allergic to, such as pollen or animal hair, your body produces a chemical called histamine. This can cause symptoms such as a runny nose or skin rashes.

Promethazine blocks the effects of histamine in your brain and this reduces symptoms.

It enters the brain in large quantities and this can make you feel drowsy.

Promethazine also blocks the effects of a chemical called dopamine, and this stops you feeling sick.

How is it different from other cough and cold remedies?

Promethazine blocks the effects of a natural chemical called acetylcholine.

This can help dry up a cough or runny nose, but can also cause side effects such as a dry mouth and dry nose.

Some cough and cold remedies claim to suppress your cough or stop you bringing up phlegm.

Although some people find them helpful, they're not usually recommended.

This is because there's little evidence that they're any more effective than simple home remedies and they're not suitable for everyone.

How long does it take to work?

Promethazine will start to make you feel sleepy around 20 minutes after you take it and may work for up to 12 hours.

If you're taking it for a cough or cold, allergies or feeling sick (nausea), your symptoms should start to improve within 20 minutes. The medicine should work for around 4 to 6 hours.

How long can I take it for?

Only take promethazine for a short time, unless your doctor says it's OK for you to take it for longer.

Speak to your pharmacist or doctor before taking promethazine for longer than the medicine leaflet recommends.

Ask them for advice if you're unsure how long you should take it for.

Is promethazine addictive?

It's unlikely that you'll get addicted to promethazine. But it's best that you only take it for a very short time, unless your doctor tells you to take it for longer.

If you have bought a medicine containing promethazine, do not take it for longer than recommended on the packet without speaking to your pharmacist or doctor first.

If you have taken promethazine for a long time and suddenly stop taking it, it's possible you might feel dizzy, sweaty or sick, have a racing heart and have trouble sleeping.

Coming off promethazine slowly can help prevent this.

Speak to your doctor if you have taken promethazine for a long time and want to stop taking it.

How is promethazine different from other antihistamines?

Promethazine is known as a drowsy (sedating) antihistamine as it makes you sleepy.

Non-drowsy antihistamines are less likely to have this effect. These include cetirizine, fexofenadine and loratadine.

Most people prefer to take a non-drowsy antihistamine as it's less likely to interfere with their everyday routine.

You might choose to take a drowsy antihistamine, however, if you're having problems falling asleep, or if symptoms like itching or coughing are keeping you awake.

There is not enough information available to say whether one antihistamine is better than another for treating allergies.

You may need to try a few different medicines to find what works best for you. Ask your pharmacist or doctor for advice if you're unsure.

Can I take more than one antihistamine at a time?

You can take 2 different antihistamines at a time, if your doctor says it's OK. If you have a severe itchy skin rash, your doctor may recommend 2 different antihistamines together for a few days.

You could take a non-drowsy antihistamine (such as cetirizine, fexofenadine or loratadine) during the day, and a drowsy antihistamine at night if itching is making it difficult to sleep.

Do not take another drowsy antihistamine together with promethazine. It'll make you very tired and sleepy.

Other drowsy antihistamines include chlorphenamine (Piriton) and diphenhydramine (Nytol Original).


Do not take 2 antihistamines together unless you have been advised to by your doctor.

Will it help me sleep?

Yes. If you take it for insomnia or take it at bedtime, promethazine will help you sleep.

If you take it during the day for other conditions, such as allergies, it might make you feel sleepy during the day as well.

Can I take it with painkillers?

Yes, you can take promethazine together with some painkillers, such as paracetamol or ibuprofen.

If you take promethazine with painkillers that contain codeine (such as co-codamol or other prescription painkillers), you may feel very tired and sleepy.

It's important to check the packaging or label of your medicine carefully. This is because some promethazine products already contain a painkiller.

Do not take extra painkillers if this is the case, as there's a risk of overdose.

Speak to your pharmacist if you're not sure whether a medicine already contains a painkiller.

Can I drive or ride a bike with it?

Do not drive a car or ride a bike if promethazine makes you sleepy during the daytime, gives you blurred vision or makes you feel dizzy, clumsy or unable to concentrate or make decisions.

This may be more likely when you first start taking promethazine, but could happen at any time (for example, when starting another medicine).

It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.

Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking promethazine. GOV.UK has more information on the law on drugs and driving.

Will it affect my fertility?

There's no evidence to suggest that taking promethazine reduces fertility in either men or women.

But speak to a pharmacist or doctor before taking it if you're trying to get pregnant.

Will it affect my contraception?

Promethazine does not affect any type of contraception, including the combined pill and emergency contraception.

Can I drink alcohol with it?

Do not drink alcohol while you're taking promethazine.

Alcohol and promethazine together can make you sleep very deeply.

You will not be able to breathe properly and may have difficulty waking up.

Is there any food or drink I need to avoid?

You can eat normally while taking promethazine.

However, do not drink alcohol. And if you take promethazine to help you sleep, try not to have drinks that contain caffeine, like coffee, tea, cola or energy drinks. Caffeine has the opposite effect to promethazine and can stop the medicine working.

Is it dangerous to take with recreational drugs?

Yes, it's dangerous to take promethazine with recreational drugs. This is because it can slow or stop your heart and lungs.

Mixing promethazine and codeine in large amounts slows down the central nervous system (brain and spinal cord), which can slow breathing and heart rate.

It's even more dangerous when taken with alcohol or other drugs and has caused people to die.

Find out more the side effects of some recreational drugs on the Frank website.

Can lifestyle changes help me sleep better?

Promethazine will only help you sleep while you're taking it, so there are a number of things you can do instead to help yourself have a good night's sleep:

  • set regular times for going to bed and waking up
  • relax before bedtime – try taking a warm bath or listening to calming music
  • use thick curtains or blinds, an eye mask and earplugs to stop you being woken up by light and noise
  • avoid caffeine, cigarettes or vapes, alcohol, heavy meals and exercise for a few hours before bedtime
  • do not watch TV or use phones, tablets or computers before going to bed
  • do not nap during the day
  • make a list of your worries and any ideas for how to solve them before you go to bed – this can help you forget about them until the morning
Can lifestyle changes help with hayfever and other allergies?

If you have hay fever, it helps if you do not spend too much time outside if the pollen count is high.

Tips for when you're outside

  • Do not cut grass or walk on grass.
  • Wear wraparound sunglasses to stop pollen getting into your eyes.
  • Put Vaseline around your nostrils to help trap pollen.
  • Shower and change your clothes after you have been outside to wash off pollen.

Tips for when you're inside

  • Keep windows and doors shut as much as possible.
  • Vacuum regularly and dust with a damp cloth.
  • Do not keep fresh flowers in the house.
  • Do not smoke or be around smoke as it makes hay fever symptoms worse.

The best way to prevent any sort of allergic reaction is to avoid the substance that you're allergic to, if you can.

There are some practical steps you can follow to help prevent allergies.