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Antihistamines


Expert reviewer Shabina Azmi, Pharmacist
Next review due July 2022

Antihistamines are medicines that you usually take to stop the symptoms of an allergic reaction like hay fever. You may also take them for insect bites and stings, or travel sickness.

 A lady travelling and holding someone's hand

Uses of antihistamines

Your doctor or pharmacist may recommend that you take antihistamines to ease allergy symptoms, such as sneezing, a runny nose, a skin rash or itching. You can be allergic to lots of different things, such as pollen (hay fever), house dust mites, certain foods, metals, pets or moulds.

You may also be recommended to take antihistamines if you have other allergic conditions, such as:


If you have an allergy, you can buy some antihistamines over the counter from a pharmacy or supermarket. If these don’t help to ease your symptoms, your doctor may be able to prescribe other antihistamines instead. See our Types of antihistamines section below.

Your doctor may recommend that you take a suitable antihistamine to stop allergy symptoms straightaway. But antihistamines don’t usually help if you have a very bad allergic reaction called anaphylaxis. This can cause:

  • difficulty breathing
  • difficulty swallowing
  • a swollen throat and tongue
  • a fast heartbeat and pulse
  • feeling faint and dizzy
  • you to be sick

Anaphylaxis can be very dangerous, so get medical help straightaway if you have any of these symptoms.

Antihistamines may also help to ease:

  • coughs and colds (usually combined with decongestants)
  • nausea and sickness (including travel sickness)
  • vertigo (feeling like everything around you is spinning)
  • insect bites and stings

Not everyone can take antihistamines, so it’s important to speak to a GP or pharmacist if you’re taking these medicines for the first time. And always make sure you read the patient information leaflet that comes with your medicine.

If you’re pregnant or breastfeeding, it’s important to speak to your GP. Some antihistamines are safe to take during pregnancy and while you’re breastfeeding. But others may affect your baby.

Children and older people can usually take antihistamines, but they may be more likely to get side-effects. Very young children shouldn’t be given antihistamines without a doctor’s advice.

How antihistamines work

Antihistamines work by blocking the effects of a chemical called histamine in your body. Histamine is made by your immune system to protect you from infections.

If you have an allergy, your immune system reacts to something that isn’t actually harmful to you like pollen. Your body then makes too much histamine, which can cause irritation and inflammation in your lungs, throat, nose, sinuses, digestive system and skin.

Types of antihistamines

If you have mild-to-moderate allergies, you can usually treat these yourself with antihistamines bought over the counter from a pharmacy or supermarkets. You can usually use simple self-help measures to ease your symptoms too.

If your symptoms are very bad, your GP can prescribe other antihistamines. But these may cause more side-effects or react with other medicines you’re taking.

Antihistamines come in different forms including:

  • tablets and capsules
  • liquids and syrups
  • eye drops
  • skin creams
  • nasal sprays

There are currently two main types of antihistamines:

  • sedating antihistamines (which may make you feel sleepy)
  • non-sedating antihistamines (which don’t usually make you feel sleepy)

You can also use some of these antihistamines to help with bites and stings and travel sickness too. It’s important to read the instructions on the pack carefully to check the dose.

Sedating antihistamines

These are the older or ‘first generation’ antihistamines. They can make you feel sleepy, because the medicines move easily from your blood to your brain. This can slow down your thinking and movement and affect your concentration. If you get these effects, do not drive, cycle or operate machinery.

Your doctor may suggest that you take a sedating antihistamine if itching from an allergy is affecting your sleep. Some of these medicines may help with travel sickness and vertigo.

Sedating antihistamines that are available from pharmacies for allergies include:

  • chlorphenamine maleate (eg Piriton)
  • clemastine (eg Tavegil)
  • cyproheptadine hydrochloride (eg Periactin)
  • promethazine hydrochloride (eg Phenergan)

You can also buy these antihistamines in a generic (unbranded) pack from a pharmacy.

There are some sedating antihistamines that can only be prescribed by your GP, but they aren’t used that often as they may cause more side-effects.

Cyclizine tablets are available over the counter from pharmacies for travel sickness or vertigo (dizziness). You can also buy promethazine teoclate tablets (eg Avomine) and cinnarizine tablets (eg Stugeron) from a pharmacy for travel sickness.

Non-sedating antihistamines

These are the newer ‘second generation’ antihistamines. They’re less likely to pass from your blood to your brain so they don’t usually make you feel so sleepy. But this varies from person to person.

Non-sedating antihistamines that you can buy from a pharmacy include:

  • acrivastine (eg Benadryl Allergy Relief)
  • cetirizine hydrochloride (eg Piriteze Allergy, Pollenshield Hayfever, Benadryl Allergy One A Day, Zirtek Allergy, Benadryl Allergy Children’s)
  • loratadine (eg Clarityn)

You can also buy these antihistamines in a generic (unbranded) pack from a pharmacy.

Your GP can also prescribe other non-sedating antihistamines, such as fexofenadine hydrochloride, but these usually have more side-effects.

Taking antihistamines

You can use antihistamines in different ways, depending on what’s causing your symptoms. If, for example, you have hay fever, you may need to continue taking antihistamines throughout the spring and/or summer. If the allergen can be removed, you may only need to take antihistamines for a short time (the time you’re exposed and for your symptoms to clear up).

How you take your medicine will also depend on the form of antihistamine. For example, taking an oral antihistamine will be different from using a nasal spray or eyedrops. For information on how to take your medicine, read the patient information leaflet that comes with it and for further information or advice, speak to you pharmacist.

Interactions of anthistamines

Antihistamines can react with other medicines. If you’re already taking other medicines, check with your pharmacist or GP before you take an antihistamine. These medicines include:


Side-effects of antihistamines

Antihistamines can cause some side-effects, so always read the patient leaflet that comes with your medicine. If you’re worried about side-effects, ask your pharmacist for advice.

Sedating antihistamines will make you feel sleepy – you may even still feel sleepy the following day. They may also affect your co-ordination, movement and concentration. Some types of sedating antihistamines may affect you more than others. Non-sedating antihistamines may still make you feel sleepy, but this is less likely. If you feel sleepy while taking any antihistamines, you shouldn’t drive, cycle or operate machines.

If you use an antihistamine nose spray, you may find it leaves a bitter taste in your mouth. This may be because you’re not using it properly, so speak to your pharmacist.

Antihistamines don’t cause very bad side-effects very often, but sometimes they can.

Older people (adults over 65) are more likely to get these very bad side-effects. Check the patient information leaflet that comes with your medicine for more information.

Medicines checklist

Our handy medicines checklist helps you see what to check for before taking a medicine.

Bupa's medicines checklist PDF opens in a new window (0.8MB)

Bupa medicines checklist

Frequently asked questions

  • It’s best not to drink alcohol while taking any type of antihistamine. Alcohol can increase the sedative side-effects of antihistamines, so you’re even more likely to feel sleepy.

    You’re more likely to experience these side-effects if you drink alcohol with sedating antihistamines such as chlorphenamine. But you may also notice this if you’re taking non-sedating antihistamines such as cetirizine.

  • Antihistamines are generally safe medicines. But if you take very high doses, you’ll be more likely to get side-effects. If you take too much of a sedating antihistamine, such as chlorphenamine, you may feel unusually sleepy or have a very dry mouth. Extremely high doses can cause fits (seizures). Taking more than five times the recommended daily dose of cetirizine can cause confusion, dizziness, diarrhoea, headaches, feeling generally unwell and shaking. An overdose of some antihistamines can also make your heart beat in an abnormal rhythm (arrhythmia).

    If you think you’ve taken too much of any antihistamine, you should get medical help straightaway. Take the medicine packet(s) with you, so the doctor can see exactly which type of antihistamine you’ve taken.

  • It’s important to read the patient information leaflet that comes with your medicine. Sometimes your doctor may prescribe or recommend that you take more than the usual maximum dose of a non-sedating antihistamine, or more than one type of antihistamine at a time. If this is recommended by your doctor, it’s OK for you to take medicines in this way, but it’s important not to do this without you doctor’s advice.

    Other medicines may contain antihistamines, such as allergy medicines, travel sickness medicines and medicines for coughs and colds. So, it’s possible to take more than the maximum recommended without realising it. It’s important to ask your pharmacist for advice if you plan on taking more than one of these medicines.

  • Antihistamines can ease the symptoms of an allergy, but they won’t stop your allergy. So, if you’re allergic to something, you should try to avoid it. It may help if you keep a symptoms diary, to see if you can figure out what’s triggering your allergy.

    If your symptoms are very bad, your GP may suggest you see an allergist or immunologist. You may need to have a ‘skin prick test’ to check exactly what’s triggering your allergic reaction. You’ll need to stop taking antihistamines (including some cough and cold medicines) several days before the test.


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Related information

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  • Reviewed by Laura Blanks, Specialist Health Editor, Bupa Health Content Team, May 2019
    Expert reviewer Shabina Azmi, Pharmacist
    Next review due July 2022



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