Diphenhydramine


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:

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.

You can also buy it mixed with other medicines, such as levomenthol, paracetamol, pholcodine and pseudoephedrine, to treat cough and cold symptoms.


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3. 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.

4. 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.

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:

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.

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

5. 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.


6. 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 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

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

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


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8. 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.

9. Pregnancy and breastfeeding

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.


10. 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.

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.


11. Common questions about diphenhydramine

Page last reviewed: 14/10/2021
Next review due: 14/10/2024