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Allergies and allergic reactions are common. About a third of all Australians have allergies at some point in their lives. However, the symptoms of allergic reactions can generally be easily and effectively treated using a group of medicines called antihistamines.

Allergies and histamine

Your body can become sensitive to things around you, like foods, plants, animals and medicines. If you are allergic to something, it is called an allergen.

When the body is exposed to allergens it releases histamine, a chemical. Histamine makes you sneeze, makes your nose run, and makes you eyes and skin itch and swell up. In a way, it is trying to get you to sneeze out or scratch away the allergen.

Treating allergies and allergic reactions with antihistamines

Antihistamines are medicines that act by blocking the body's response to histamine. This reduces the severity of the reaction and eases the symptoms of allergy. Antihistamines are commonly used in the treatment of a number of conditions related to allergies and hypersensitivities like:

Some antihistamines can also be used to treat non-allergy-related conditions, such as motion sickness, insomnia and heartburn or indigestion.

Oral antihistamines can be used to treat all of the symptoms of an allergic reaction. Others come as eye drops or nasal sprays, for treating specific symptoms only. Some oral antihistamines may have a sedative effect, but others are non-sedating or non-drowsy.

Antihistamines don't treat very severe allergic reactions like anaphylaxis, as they work too slowly.

Side effects of antihistamines

Some people get side effects from oral antihistamines like:

  • tiredness
  • drowsiness
  • headache
  • dry mouth
  • upset stomach.

They usually don't last long.

If you use antihistamines you should be careful when operating machinery, such as driving a car. Even non-sedating antihistamines can make some people drowsy.

You should talk to a pharmacist or doctor before taking an antihistamine if you:

People with porphyria should talk to their doctor or pharmacist before taking antihistamines.

If you have any questions or concerns about antihistamines, please talk to your doctor or pharmacist.

Last reviewed: August 2017

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