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Antihistamines: What They Do, Medicines

Also in: हिन्दी தமிழ் मराठी తెలుగు ಕನ್ನಡ বাংলা ગુજરાતી മലയാളം

Antihistamines are medicines that block histamine, a chemical the body releases during an allergic reaction. They are used to relieve sneezing, a runny or itchy nose, itchy watery eyes, and itchy rashes such as hives. Older types, such as chlorphenamine, promethazine and hydroxyzine, often cause drowsiness, while newer types, such as cetirizine, levocetirizine, fexofenadine and loratadine, cause it less often. Medicines that block histamine in the stomach, such as famotidine, are a different group used for acidity.

Pharmacist review in progress. This page is based on the sources listed below and is being checked by our registered pharmacist.

How do Antihistamines work?

When an allergen such as pollen or dust enters the body, mast cells release histamine, which makes small blood vessels leak and nerves itch. Antihistamines in this group block the H1 receptor that histamine acts on, which reduces sneezing, itching, runny nose and swelling. Older antihistamines also enter the brain easily, which is why they make people sleepy.

Active ingredients of this type

These active ingredients belong to Antihistamines. They are listed A to Z.

  • Levocetirizine: Levocetirizine is a newer antihistamine used to relieve allergy symptoms such as sneezing, a runny or itchy nose and itchy, watery eyes.

Common questions

Do antihistamines cause drowsiness?

Older antihistamines often do, and the effect can last into the next day. Newer ones such as levocetirizine and fexofenadine cause it less often, but some people still feel sleepy. Do not drive or use machines until you know how one affects you, and avoid alcohol, which adds to drowsiness.

Can antihistamines be taken for a cold?

Antihistamines relieve allergy symptoms; they do not act on the virus that causes a cold. Many cold remedies contain an antihistamine along with other ingredients, so check labels to avoid taking two antihistamines at once, and ask a pharmacist before giving any to a child.

Sources

  1. Antihistamines. NHS (UK)
  2. Antihistamines. StatPearls, National Center for Biotechnology Information (NCBI), US National Library of Medicine
  3. Xyzal 5 mg film-coated tablets: Summary of Product Characteristics. electronic medicines compendium (emc), UK
  4. ATC/DDD Index: R06A Antihistamines for systemic use. WHO Collaborating Centre for Drug Statistics Methodology