What Is an Antihistamine?
Wellness & SelfcareDrugs

What Is an Antihistamine?

By blocking the effects of histamines, this class of drugs can treat allergies and many other ailments.
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Updated on September 30, 2023
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An antihistamine is a type of medicine used to treat common allergy symptoms, such as sneezing, watery eyes, hives, and a runny nose.

More than 100 million Americans suffer from some type of allergy each year, according to the Asthma and Allergy Foundation of America, including about 81 million with seasonal allergies, such as hay fever.

Certain antihistamines are also sometimes used to treat motion sickness, nausea, vomiting, dizziness, cough, sleep problems, anxiety, and Parkinson’s disease.

The drugs work by blocking the effects of histamine, a substance in the body that can cause allergy symptoms, notes MedlinePlus.

Antihistamines come in different forms, such as capsules, tablets, liquids, eye drops, injections, and nasal sprays. They can be purchased over-the-counter (OTC) or given as a prescription, per the Mayo Clinic.

Some antihistamines are taken daily, while others are used only when symptoms occur.

Types of Antihistamines

Some common antihistamines include:

  • fexofenadine (Allegra)
  • azelastine (Astelin, Astepro) nasal sprays
  • hydroxyzine (Atarax, Vistaril)
  • diphenhydramine (Benadryl)
  • chlorpheniramine (Chlor-Trimeton)
  • desloratadine (Clarinex)
  • loratadine (Claritin, Alavert)
  • cyproheptadine (Periactin)
  • brompheniramine and phenylephrine (Dimetane)
  • emedastine (Emadine) eye drops
  • levocabastine (Livostin) eye drops
  • azelastine (Optivar) eye drops
  • carbinoxamine (Palgic)
  • levocetirizine (Xyzal)
  • clemastine (Tavist)
  • cetirizine (Zyrtec)

Antihistamine Side Effects

Per MedlinePlus, common side effects of antihistamines include:

  • Drowsiness or sleepiness
  • Dizziness
  • Dry mouth, nose, or throat
  • Decreased appetite
  • Upset stomach
  • Thickening of mucus
  • Changes in vision
  • Feeling nervous, excited, or irritable

Antihistamine Precautions

Before taking an antihistamine, tell your doctor about all medical conditions you have, especially:

Don’t drive or perform activities that require alertness until you know how the antihistamine you’re taking affects you.

Follow the instructions on your prescription or package label carefully when taking an antihistamine. Don’t take more of the medicine than is recommended.

Tell your doctor about all prescription, nonprescription, illegal, recreational, herbal, nutritional, or dietary drugs you’re taking before starting on an antihistamine.

You may need to avoid grapefruit and grapefruit juice while taking an antihistamine, as they can affect how these drugs work in your body. Talk to your doctor if this is a concern.

Antihistamines and Alcohol

Alcohol may worsen certain side effects of antihistamines, per MedlinePlus.

Avoid drinking alcohol while taking these medicines.

Antihistamines and Pregnancy

Tell your doctor if you’re pregnant, or might become pregnant, while using an antihistamine.

You’ll have to discuss the risks and benefits of taking the medicine during pregnancy.

Also, talk to your healthcare provider before taking antihistamines if you’re breastfeeding.

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