1. About diphenhydramine
Diphenhydramine is an antihistamine medicine that relieves the symptoms of allergies. It's known as a drowsy (sedating) antihistamine and is more likely to make you feel sleepy than other antihistamines. It's used for:
- short-term sleep problems (insomnia), including when a cough, cold or itching is keeping you awake at night
- cough and cold symptoms
- hay fever
- eczema, hives (urticaria) and insect bites and stings
You can buy diphenhydramine from pharmacies and it is also available on prescription.
It comes as tablets and a liquid that you swallow. For skin allergies like hives or bites and stings it's also available as a cream. The cream is much less likely to make you feel sleepy than the tablets or liquid.
2. Key facts
- To help you sleep, you'll usually take diphenhydramine 20 minutes before you go to bed. It normally takes about 30 minutes to work.
- Common side effects include feeling sleepy, dizzy or unsteady on your feet. You may also have difficulty concentrating and have a dry mouth.
- You can become dependent on diphenhydramine if you take it continuously for a period of time. It may also stop working as well. Speak to your doctor if you need to take it for more than 2 weeks.
- Do not drink alcohol while taking diphenhydramine. Alcohol increases the risk of side effects.
- When diphenhydramine is mixed with other medicines, brand names include Benylin Chesty Coughs, Benylin Children's Night Coughs, Covonia Night Time Formula, Panadol Night Pain and Unicough.
3. Who can and cannot take diphenhydramine
Diphenhydramine can be taken by most adults and young people aged 16 years and above. You can sometimes give diphenhydramine to children, depending on their age and their symptoms. Ask your pharmacist for advice.
Giving diphenhydramine to children
For cough and cold symptoms, you can give diphenhydramine tablets and liquid to children over the age of 6. For allergy symptoms, you can give it to children over 12. Check with your pharmacist or doctor to make sure a product is suitable for your child.
You can also use diphenhydramine cream on children for:
Important: Warning for children
Do not give your child diphenhydramine to help them get to sleep. Diphenhydramine is only suitable for sleep problems in people aged 16 years and above.
Who may not be able to take diphenhydramine
Diphenhydramine is not suitable for some people. To make sure it's safe for you, tell your doctor or pharmacist if you:
- have ever had an allergic reaction to diphenhydramine or any other medicine
- have lung problems, such as asthma or chronic obstructive pulmonary disease (COPD), or an illness that creates a lot of phlegm
- have an eye problem called primary angle closure glaucoma
- have a blockage in your stomach or gut
- have kidney or liver problems
- have problems peeing or emptying your bladder
- have epilepsy or any other health problem that causes fits (seizures)
- are due to have an allergy test – diphenhydramine can affect your results, so you may need to stop taking it a few days before your test – ask a pharmacist or your doctor for advice
- are unable to have any alcohol – some liquid diphenhydramine products contain a small amount of alcohol, so check the ingredients and the packaging carefully
4. How and when to take or use diphenhydramine
If you or your child have been prescribed diphenhydramine, follow your doctor's instructions about how and when to take it.
Only take or use diphenhydramine 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've bought diphenhydramine or any medicine containing diphenhydramine from a pharmacy, follow the instructions that come with the packet, or ask a pharmacist for advice.
The instructions will be different depending on the type of medicine you buy, and the other medicines it's mixed with.
If you're aged over 65, start with the lower dose, as you may be more likely to get side effects.
The usual dose depends on the type of diphenhydramine medicine you're taking, and why.
Dosage for short-term insomnia
Diphenhydramine comes as 25mg and 50mg tablets. You'll usually take 50mg, 20 minutes before you go to bed.
Dosage for cough and cold symptoms
Diphenhydramine comes mixed with other medicines to treat the symptoms of coughs and colds. It comes as tablets and as a liquid that you swallow. The usual dose depends on the type of medicine you're taking. Check the instructions on the packaging carefully, or ask your doctor or pharmacist if you're unsure.
Dosage for hay fever and allergies
Diphenhydramine comes as 25mg and 50mg tablets. The usual dose is 25mg or 50mg, taken 3 or 4 times a day. Try to space your doses evenly throughout the day.
Dosage for insect bites, stings and eczema
Diphenhydramine comes as a cream which you use once or twice a day. You'll only need a small amount, enough for a thin layer.
How to take or use it
You can take diphenhydramine tablets and liquid with or without food.
How to take diphenhydramine tablets
Always take your diphenhydramine tablets with a drink of water. Swallow them whole. Do not chew them.
How to take diphenhydramine liquid
Liquid medicines containing diphenhydramine come with a plastic syringe or spoon to help you measure the right dose. If you do not have a syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not measure the right amount.
How to use diphenhydramine cream
With the cream, put a small amount onto the affected area and smooth it in gently. Do not use it on large areas of skin. Keep the cream away from your eyes, mouth and nose. Remember to wash your hands afterwards, unless you're treating your hands.
What if I forget to take or use it?
If you're taking diphenhydramine to help you sleep and you forget to take it by bedtime, skip your missed dose and start again the next evening.
If you're taking any other medicine containing diphenhydramine and forget to take a dose, take your medicine when you next need it to ease your symptoms.
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 or use too much?
Too much diphenhydramine can be dangerous.
If you've taken more than the usual dose you may:
- feel very sleepy
- feel sick (nauseous)
- get blurry eyesight
- feel your heart beating very fast
In serious cases you can become unconscious and may need emergency treatment in hospital.
Do not use diphenhydramine cream at the same time as other products containing diphenhydramine. This can lead to overdose.
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 diphenhydramine packet or leaflet inside it plus any remaining medicine with you.
5. Side effects
Like all medicines, diphenhydramine can cause side effects, although not everyone gets them. However, you may be more likely to get them if you're over 65.
Common side effects
Common side effects happen in more than 1 in 100 people. Talk to your doctor or pharmacist if these side effects bother you or do not go away:
- feeling sleepy, or drowsy, during the daytime
- dry mouth
- feeling dizzy or unsteady on your feet, or having difficulty concentrating
Diphenhydramine cream can sometimes make your rash worse. It may also make your skin sensitive to sunlight.
Serious side effects
Urgent advice: Contact 111 for advice now if:
- you have a fast or irregular heartbeat (palpitations)
- you feel any numbness or pins and needles
- you feel confused or very restless
Immediate action required: Call 999 if:
- you or child has had a seizure or fit
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to diphenhydramine.
Immediate action required: Call 999 or go to A&E now 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.
Other side effects
These are not all the side effects of diphenhydramine. For a full list, see the leaflet inside your medicine packet.
You can report any suspected side effect using the Yellow Card safety scheme.
6. How to cope with side effects of diphenhydramine
What to do about:
- feeling sleepy, or drowsy, during the daytime – drowsiness usually wears off 8 hours after a dose. Do not drive, ride a bike or use tools or machinery if you're feeling this way.
- dry mouth – chew sugar-free gum or suck sugar-free sweets.
- feeling dizzy or unsteady on your feet, or difficulty concentrating – if diphenhydramine makes you feel this way, stop what you're doing and sit or lie down until you feel better. If the feeling does not go away or is worrying you, do not take any more medicine and speak to a pharmacist or your doctor.
7. Pregnancy and breastfeeding
Diphenhydramine and pregnancy
While diphenhydramine can be used during pregnancy, it is not normally recommended. This is because of the side effects, which may be more significant during pregnancy. Discuss with your doctor or pharmacist other medicines, such as chlorphenamine, that may more suitable.
If you have difficulty sleeping while you're pregnant, your doctor or midwife may suggest ways to improve your sleep routine, like relaxing, and avoiding naps.
If you have a cough or cold, you can help to ease your symptoms by resting, drinking plenty of fluids and taking paracetamol.
Diphenhydramine and breastfeeding
If your doctor or health visitor says your baby is healthy, you can take diphenhydramine while you're breastfeeding, but it's better to take occasional doses or only take it for a short time.
Diphenhydramine passes into breast milk in very small amounts. Although it's unlikely to cause any side effects in your baby, it is a drowsy antihistamine, so could make your baby sleepy.
If you're breastfeeding, or planning to breastfeed, talk to your doctor. They may recommend similar antihistamines, called loratadine and cetirizine, that are more suitable while you're breastfeeding.
Talk to your doctor, pharmacist, midwife or health visitor if your baby is not feeding as well as usual, seems unusually sleepy, seems irritable, or if you have any other concerns about your baby.
Non-urgent advice: Tell your doctor if you're:
- trying to get pregnant
8. Cautions with other medicines
Some medicines can affect the way diphenhydramine works, and increase the chances of you having side effects. Check with your pharmacist or doctor if you're taking:
- antidepressants, such as venlafaxine or a monoamine oxidase inhibitor such as phenelzine
- metoprolol, a heart medicine
- any medicine that makes you drowsy, gives you a dry mouth, or makes it difficult for you to pee – taking diphenhydramine might make these side effects worse
If you're taking a cough or cold remedy or a painkiller containing diphenhydramine, check carefully what the other ingredients are. For example, check whether it contains paracetamol. Ask your pharmacist for advice before you take this medicine together with any other painkillers or medicines.
Mixing diphenhydramine with herbal remedies and supplements
There might be a problem taking some herbal remedies and supplements alongside diphenhydramine, especially ones that cause side effects such as sleepiness, a dry mouth or making it difficult to pee.
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 diphenhydramine
How does diphenhydramine work?
Diphenhydramine is a medicine called an antihistamine. It is classed as a drowsy (sedating) antihistamine.
When you come into contact with something you're allergic to, your body produces a chemical called histamine. This can cause symptoms such as a runny nose or skin rashes.
Diphenhydramine 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.
Diphenhydramine also blocks the effects of another chemical called acetylcholine. This can help a cough or runny nose but can also cause side effects such as a dry mouth and dry nose.
How long does it take to work?
If you're taking diphenhydramine for short-term sleep problems, it will start to make you feel drowsy around 20 to 30 minutes after you take it.
For coughs and colds, your symptoms will normally 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 diphenhydramine for a short time.
You can become dependent on it if you take it continuously for too long. To avoid this, follow the instructions that come with the medicine and only take diphenhydramine for a very short time, unless your doctor advises otherwise.
Is diphenhydramine addictive?
It is unlikely that you'll become addicted to diphenhydramine but it's best to only take it for a short time. You can become dependent on diphenhydramine if you take it continuously for too long.
Follow the instructions that come with the medicine and only take diphenhydramine for a very short time, unless your doctor advises otherwise.
Can I take more than one antihistamine at a time?
If you have a severe itchy skin rash, your doctor may recommend taking 2 different antihistamines at the same time for a few days.
As well as taking a non-drowsy antihistamine during the day (such as fexofenadine, cetirizine or loratadine), your doctor may advise that you take a drowsy antihistamine at night if itching is making it difficult to sleep.
Do not take another drowsy antihistamine together with diphenhydramine. It will make you very tired and sleepy. Other drowsy antihistamines include chlorphenamine (Piriton), promethazine (Phenergan) and hydroxyzine (Atarax or Ucerax).
Do not take 2 antihistamines together unless you've been advised to by your doctor.
What's the difference between diphenhydramine and other antihistamines?
Diphenhydramine is known as a drowsy, or 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 is not enough information 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.
How is it different to other cough and cold remedies?
Diphenhydramine 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.
Can I take it with painkillers?
If you take diphenhydramine with painkillers that contain codeine (such as co-codamol) or other prescription painkillers, you may feel very tired and sleepy. 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 diphenhydramine 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 diphenhydramine makes you sleepy during the day, 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 diphenhydramine 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 diphenhydramine. 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 diphenhydramine reduces fertility in either men or women.
Can I drink alcohol with it?
Do not drink alcohol while you're taking diphenhydramine.
Alcohol and diphenhydramine together can make you sleep very deeply. You will not be able to breathe properly and you may have difficulty waking up.
Is there any food or drink I need to avoid?
You can eat normally while taking diphenhydramine.
However, do not drink alcohol. If you are taking diphenhydramine to help you sleep, you should also try not to drink anything that contains caffeine, such as coffee, tea, cola or energy drinks. Caffeine has the opposite effect to diphenhydramine on your body and can stop it working.
Does diphenhydramine make you put on weight?
There's no evidence that diphenhydramine makes you put on weight.
Can lifestyle changes help me sleep better?
There are a number of things you can try 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 in bed, or before bedtime
- 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 hay fever and other allergies?
If you have hay fever, it will help if you do not spend too much time outside when 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 (petroleum jelly) around your nostrils to help trap pollen.
- Shower and change your clothes after you've 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 because 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 you avoid common allergens.