Antihistamines and allergies

Antihistamines are a group of medicines used to help relieve the symptoms of allergies.
You may be advised to use antihistamines for the following conditions:

  • Hayfever – an allergy to pollen which can cause a runny nose, sneezing and itchy eyes.
  • Allergic skin conditions such as Eczema and Urticaria (Hives) - symptoms often include itchy, red, dry skin.
  • Allergic Rhinitis – inflammation of the nose caused by an allergy which often includes a runny nose and sneezing.
  • Mild allergic reactions to insect bites or stings.
  • Allergic conjunctivitis - swollen and inflamed eyes which may include a watery discharge.

You may also be advised to take antihistamines if you suffer from motion sickness, stomach ulcers or have problems with sleep.

There are a range of antihistamines available both on prescription and to buy over the counter (OTC). They currently fall into two groups:

1. First generation antihistamines - such as diphenhydramine and chlorphenamine. These can have a sedative effect and are usually best avoided during the daytime as they may cause you to feel drowsy which may affect your ability to carry out normal day to day tasks safely.

2. Second and third generation antihistamines – such as loratidine and cetirizine. These are usually more frequently recommended as they do not have a sedative effect but will provide relief from symptoms.

Antihistamines come in different forms including tablets, syrup (liquid medicine), nasal sprays, creams and lotions. The most common forms used for allergies are either tablets or syrups.

I’ve been prescribed antihistamines to help me sleep, is this right?
One of the most common side effects of some allergic reactions is a lack of sleep due to the uncomfortable symptoms, such as constant itchiness. First generation antihistamines, those which have a sedative effect, may be prescribed by your doctor to help relieve symptoms and allow sufferers to get to sleep. They are best taken about an hour before going to bed and you should avoid driving until the effects have worn off. More information can be found in the patient information leaflets included with your medication.

Used for children, sedative antihistamines are often prescribed in high doses for short periods of time and are generally used to help get through flare-ups.

Side effects of antihistamines
As with all medication, there may be some side effects in a small number of people who take antihistamines. These can include:

  • drowsiness (feeling sleepy, especially if first generation antihistamines have been prescribed)
  • headaches, which may include blurred vision
  • dizziness
  • constipation (difficulty in passing stools).

Speak to your doctor or pharmacist if you experience any of the side effects listed above.
If you’re taking any other medication or unsure as to which type of histamine will best suit your needs, speak with your doctor or pharmacist.

Sources used in writing this article are available on request.

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Information written by the talkhealth team

Last revised: 29 August 2017
Next review: 29 August 2020