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 or cold, or itching, is keeping you awake at night – brand names include Nytol Original, Nytol One-a-Night and Sleepeaze
  • cough and cold symptoms – brand names include Benylin Chesty Coughs and Covonia Night Time Formula
  • hay fever – brand names include Histergan
  • eczema, hives (urticaria), insect bites and stings – brand names include Histergan

You can buy Diphenhydramine from pharmacies and supermarkets. Diphenhydramine is also available on prescription.

It comes as tablets, capsules 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, capsules or liquid.

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

  • Avoid drinking alcohol while taking diphenhydramine. Alcohol increases the risk of side effects.
  • To help you sleep, you’ll usually take your medicine 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 a dry mouth.
  • Diphenhydramine is also called by the brand names Histergan, Nytol Original, Nytol One-A-Night and Sleepeaze.
  • When it’s mixed with other medicines, brand names include Benylin Chesty Coughs, Benylin Children’s Night Coughs, Covonia Night Time Formula, Panadol Night Pain and Unicough.

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.

Diphenhydramine isn’t suitable for some people. Tell your doctor or pharmacist if you:

  • have had an allergic reaction to diphenhydramine or any other medicines in the past
  • have lung problems, such as asthma or COPD, or an illness that creates a lot of phlegm
  • have an eye problem called primary angle closure glaucoma
  • have a stomach ulcer, or 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
  • have an intolerance to, or cannot absorb, some sugars such as lactose or sorbitol
  • 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

Giving diphenhydramine to children

For some symptoms, you can give diphenhydramine to children over the age of 6 years. Check with your pharmacist or doctor to make sure whether a product is suitable for your child.

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.

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 don’t go away:

  • feeling sleepy during the daytime
  • dry mouth
  • feeling dizzy or unsteady on your feet, or having difficulty concentrating

Diphenhydramine cream can sometimes make rashes worse. It may also make your skin sensitive to sunlight.

Serious side effects

Tell your doctor straight away if you:

  • have an irregular heartbeat
  • an increased awareness of your heartbeat
  • feel any numbness or pins and needles
  • feel confused or very restless
  • have a fit (seizure)

If someone around you is having a fit, call 999 straight away.

Serious allergic reaction

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

What to do about:

  • feeling sleepy during the daytime – drowsiness usually wears off 8 hours after a dose. Do not drive 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 doesn’t go away or is troubling you, do not take any more medicine and speak to a pharmacist or your doctor.

Diphenhydramine isn’t normally recommended during pregnancy.

This is because there isn’t enough information to be sure it’s safe. If you take diphenhydramine towards the end of your pregnancy, there’s a risk your baby may be born with some of the side effects.

If you have insomnia while you’re pregnant, your doctor or midwife may suggest ways to improve your sleep routine – like relaxing, and avoiding naps. If this doesn’t work, your doctor may prescribe a different antihistamine called promethazine to help you sleep.

If you have a cough or cold, you can help to ease your symptoms by resting, drinking plenty of fluids and taking everyday painkillers such as paracetamol.

Diphenhydramine and breastfeeding

Diphenhydramine isn’t normally recommended when breastfeeding, as small amounts of the medicine pass into your breast milk. It may also reduce the amount of milk you produce.

Talk to your doctor, as other medicines might be better while you’re breastfeeding. It’s usually safe to take similar antihistamines called loratadine and cetirizine while you’re breastfeeding. If you need a drowsy antihistamine to help you sleep, your doctor may recommend chlorphenamine.

However, speak to your doctor before taking any antihistamine if your baby was premature, had a low birth weight or has health problems.

Some medicines and diphenhydramine interfere with each other 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 make it difficult to pee.

How does diphenhydramine work?