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Antihistamines

Key points

  • Antihistamines are medicines that are often used to treat allergic reactions, such as hay fever (allergic rhinitis).
  • There are two types of antihistamines: sedating and non-sedating. Sedating antihistamines can make you drowsy.
  • Antihistamines work by blocking the effect of a chemical in your body called histamine and so help to ease allergic reactions.
  • Antihistamines can be taken as tablets, nasal sprays, drops, liquids or applied as creams.

Antihistamines are medicines that are commonly used to treat allergic reactions such as hay fever (allergic rhinitis). They may also be used to treat sickness, vertigo and insomnia.

Why would I take antihistamines?

Antihistamines can be used to treat a range of conditions. You might take them to ease allergic reactions. These include:

You may also take some types of antihistamines to help relieve the symptoms of sickness, vertigo and insomnia.

What are the main types of antihistamines?

There are two main types of antihistamines, which are described below.

Sedating

The older types of antihistamines are sometimes referred to as sedating antihistamines. This type of antihistamine can affect your brain, causing you to become drowsy. An example of a sedating antihistamine is chlorphenamine maleate (eg Piriton).

Non-sedating

The newer types of antihistamines are sometimes referred to as non-sedating antihistamines. This type of antihistamine has less of an effect on your brain and won’t make you so drowsy. Acrivastine (eg Benadryl) is an example of a non-sedating antihistamine.

How do antihistamines work?

Your immune system protects you from harmful substances such as bacteria and viruses. It does this by producing antibodies which help to remove these from your body.

In an allergic reaction, your immune system reacts to a harmless substance such as pollen, because it mistakes it for a harmful one. When this happens, a chemical called histamine is released by your immune system. Histamine is very useful because it helps damaged tissue to heal. However, this process can also cause symptoms such as:

  • a runny nose
  • itchy eyes, nose, throat and skin
  • sneezing
  • urticaria

Antihistamines work by blocking the effect of histamine in your body. This helps to prevent inflammation and eases allergic reactions.

If you have a severe allergic reaction, your symptoms may include:

  • difficulty breathing
  • swollen lips and eyelids
  • a fast heartbeat

This type of allergic reaction is called anaphylaxis. If you have anaphylaxis, it’s important that you get medical help immediately as it can be very serious. You will be given an injection of adrenaline if you have anaphylaxis. Sometimes an injection of an antihistamine is used in addition to adrenaline.

How to take antihistamines

You can buy some antihistamines from pharmacies without a prescription. Examples include chlorphenamine maleate (eg Piriton), loratadine (eg Clarityn) and cetirizine (eg Zirtek). Some antihistamines are only available on prescription from your GP as they could have side-effects or interactions with other medicines you might be taking.

Depending on what you need antihistamines for; you can take them as tablets, liquids, nasal sprays or a cream. Only use antihistamine creams for a short amount of time as they may cause an allergic reaction. Don’t use antihistamine creams on areas of broken skin, unless your GP has said that you can do so.

Special care

If you’re pregnant, it’s recommended that you don’t take antihistamines. This is also true if you’re breastfeeding because antihistamines can get into your breast milk. If you feel you need to be treated with antihistamines while pregnant or breastfeeding, see your GP for advice.

If you have epilepsy, you must get advice from your GP before taking a sedating antihistamine. You should not take this type of antihistamine if you have severe liver disease.

Side-effects of antihistamines

This section doesn’t include every possible side-effect of antihistamines. Always read the patient leaflet that comes with your medicine and ask your pharmacist for advice.

The sedating forms of antihistamines will make you feel very drowsy and can affect your coordination. Therefore, it’s important that you don’t drive or drink alcohol for 24 hours after taking a sedating antihistamine. Alcohol can increase the sedative effect of these types of antihistamines. You should not drink alcohol if you’re taking these antihistamines.

With the newer, non-sedating antihistamines drowsiness is less of a problem.
Side-effects that are more common with the older, sedating antihistamines include:

  • headache
  • difficulty passing urine
  • dry mouth
  • blurred vision
  • feeling sick or vomiting

Other, rare side-effects of antihistamines include:

  • low blood pressure
  • arrhythmia (abnormal heart rhythm)
  • dizziness
  • confusion
  • depression
  • disturbed sleep
  • tremor (a slight shaking of part of your body, often your hands)
  • allergic reactions (including swelling, rashes, breathing difficulties)
  • blood or liver problems

Children and adults over 65 are more likely to get side-effects.

Interactions of antihistamines with other medicines

Check with your GP or pharmacist before you take any other medicines at the same time as antihistamines.

Tricyclic antidepressants interact with antihistamines and can increase the drowsiness side-effect. The antihistamine mizolastine can also interact with some other medicines and may cause a serious abnormal heart rhythm. This medicine is only available on prescription from your GP, who will give you advice if you need to take it.

Some antifungal (ketoconazole) medicines and antibiotics (erythromycin) can increase the amount of non-sedating antihistamine in your body.

It’s best not to drink alcohol while taking antihistamines of any type as this will increase the drowsiness side-effect.

Names of common antihistamines

Antihistamine medicines are shown in the table below. It’s important to remember that you may not be able to buy some of these medicines over the counter as they may be prescription only.

All medicines have a generic name. Many medicines also have one or more brand name. Generic names are written in lower case, whereas brand names start with a capital letter.

Generic names Examples of common brand names
Non-sedating antihistamines  
acrivastine Benadryl Allergy Relief
bilastine Ilaxten
cetirizine hydrochloride Benadryl Allergy Oral Syrup, Benadryl for Children Allergy Solution, Benadryl One-a-Day Relief, Piriteze Allergy, Pollenshield Hayfever Relief, Zirtek Allergy Relief
desloratadine Neoclarityn
fexofenadine hydrochloride Telfast
levocetirizine hydrochloride Xyzal
loratadine Clarityn Allergy
mizolastine Mizollen
Sedating antihistamines  
alimemazine tartrate Vallergan
chlorphenamine maleate Piriton
clemastine Tavegil
cyproheptadine hydrochloride Periactin
hydroxyzine hydrochloride Atarax, Ucerax
ketotifen Zaditen
promethazine hydrochloride Phenergan
For the eyes and nose  
antazoline (with xylometazoline) Otrivine-Antistin (for eyes)
azelastine Optilast (for eyes), Rhinoblast (for nose)
epinastine Relestat (for eyes)
ketotifen Zaditen (for eyes)
olopatadine Opatanol (for eyes)
Creams and lotions for the skin  
diphenhydramine hydrochloride Benadryl Skin Allergy Relief Cream
mepyramine maleate Anthisan, Wasp-Eze Bites and Stings spray, Wasp-Eze
Travel sickness and vertigo/nausea  
meclozine hydrochloride Sea-legs
cyclizine Valoid
cinnarizine Stugeron
Sleep aids  
diphenhydramine hydrochloride Nytol, Nytol One-a-Night
promethazine hydrochloride Sominex

 

Reviewed by Kuljeet Battoo, Bupa Health Information Team, June 2014.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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