- Avoid drinking alcohol while taking promethazine. Alcohol increases the risks of side effects.
- To help you sleep, you'll usually take promethazine 20 minutes before you go to bed. It normally takes about 30 minutes to work.
- For preventing travel sickness, you can usually take promethazine the night before a long journey or 1 to 2 hours before a short journey.
- Common side effects include feeling sleepy, headaches, nightmares and feeling dizzy, restless or confused.
- Promethazine is known by the brand names Avomine, Phenergan and Sominex.
- When promethazine is mixed with other medicines, it's also known by the brand names Day & Night Nurse, Fedril and Night Nurse.
Promethazine can be taken by most adults and children aged 2 years and above.
Promethazine isn't suitable for some people. Tell your doctor or pharmacist if you:
- have had an allergic reaction to promethazine or any other medicines in the past
- 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 fits
- have an intolerance to, or can't absorb, some sugars, such as lactose or sorbitol
- 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.
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 or supermarket, follow the instructions that come with the packet, or ask your pharmacist for advice.
How much to take
Promethazine comes in 10mg, 20mg and 25mg tablets and a liquid that you swallow.
If you're taking liquid promethazine, follow the instructions that come with the medicine for how much to take.
If you're taking promethazine tablets, your dose depends on why you're taking it:
- short-term insomnia - you'll usually take 20 to 50mg at night
- hay fever - you'll usually take 10mg twice a day to 20mg 3 times a day
- hives - you'll usually take 10mg twice a day to 20mg 3 times a day
- preventing travel sickness - 25mg taken 1 to 2 hours before a short journey or 25mg the night before a long journey
- treating travel sickness - take 25mg as soon as possible and 25mg the same evening, followed by 25mg the following evening (if you need it)
- morning sickness and vertigo - the dose can vary from 25mg a day to 25mg 4 times a day
Promethazine comes mixed with other ingredients for cough and cold symptoms - the usual dose depends 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.
Doses are lower for children. Your doctor will use your child's age to work out the right dose.
How to take it
You can take promethazine tablets, capsules and liquid with or without food.
Always take your promethazine tablets or capsules with a drink of water. Swallow them whole. Do not chew them.
Liquid medicines containing promethazine come with a plastic syringe or spoon to help you measure out the right dose.
If you don't have a syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as you won't get the right amount.
What if I forget my medicine?
For travel 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 forget doses often, 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 have accidentally taken too much, you may:
- feel very sleepy
- have a very fast, uneven or pounding heartbeat (palpitations)
- have breathing problems
In serious cases, you can become unconscious or have 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 aren't there (hallucinations)
- have an uneven heartbeat
Call your doctor straight away if you take too much promethazine by accident
If you need to go to a hospital accident and emergency (A&E) department, 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.
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 don't go away:
- feeling tired during the daytime
- feeling dizzy or unsteady on your feet, or having difficulty concentrating
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 experience side effects such as:
- feeling confused
- dry mouth
- blurred vision
- difficulty peeing
Children are more likely to experience side effects such as feeling restless or excited.
Serious side effects
Call your doctor straight away if you have:
- yellowing of the skin or whites of the eyes - these can be signs of liver problems
- bruising or bleeding that's more than normal
- 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.
Call 999 or go to A&E if:
- you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
- you're wheezing
- you get tightness in the chest or throat
- you have trouble breathing or talking
- your mouth, face, lips, tongue or throat start swelling
You could be having a serious allergic reaction and may need immediate treatment in hospital.
These aren't all the side effects of promethazine. For a full list, see the leaflet inside your medicine packet.
You can report any suspected side effect to the UK safety scheme.
What to do about:
- feeling sleepy during the daytime - this usually wears off 12 hours after a dose. Do not drive or use tools or machinery if you're feeling this way.
- nightmares - speak to your pharmacist or doctor if these don't 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 doesn't go away or is troubling you, do not take any more medicine and speak to a pharmacist or your 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.
Your doctor may want to prescribe promethazine for morning sickness when other treatments haven't worked.
Pregnant women have taken promethazine with no harmful effects to the mother or baby. But for safety it's best to take it for the shortest possible time.
For more information about how promethazine can affect you and your baby during pregnancy, read the leaflet about the best use of medicines in pregnancy (BUMPS).
Promethazine and breastfeeding
Promethazine passes into breast milk in small amounts. Talk to your doctor, as other medicines might be better while you're breastfeeding.
If you need a drowsy antihistamine to help you sleep, your doctor may recommend chlorphenamine.
But speak to your doctor before taking any antihistamine if your baby was premature, had a low birth weight, or has health problems.
Tell your doctor if you're trying to get pregnant, already pregnant or breastfeeding.
Some medicines and promethazine interfere with 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
- 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.
Tell your doctor or pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.
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.
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 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?
You should 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.
Not a lot is known about taking promethazine for a long time, so there's more chance of having side effects.
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.
What's the difference between promethazine and other antihistamines?
Promethazine is known as a drowsy (sedating) antihistamine as it makes you sleepy.
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 isn't 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 you have a severe itchy skin rash, your doctor may recommend 2 different antihistamines together for a few days.
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 night time, promethazine will help you sleep.
If you take it during the day for other conditions, such as allergies, it might cause daytime sleepiness, too.
Can I take it with painkillers?
Do not drive, ride a bike or operate machinery or tools if this happens to you.
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.
GOV.UK has more information on the law on drugs and driving. Talk to your doctor or pharmacist if you're unsure whether it's safe for you to drive while taking promethazine.
Will it affect my fertility?
There's no firm evidence to suggest that taking promethazine will reduce fertility in either men or women.
But speak to a pharmacist or your doctor before taking it if you're trying to get pregnant.
Will it affect my 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 won't 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.
But avoid alcohol and drinks that contain caffeine, like coffee, cola, or energy drinks.
Caffeine has the opposite effect to promethazine on your body and stops it 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.
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 bed time
- don't watch TV or use phones, tablets or computers before going to bed
- don't 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'll help if you don't spend too much time outside if the pollen count is high.
Tips for when you're outside:
- don't 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
- don't keep fresh flowers in the house
- don't 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.