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Antihistamines for Allergies

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Treating allergies can involve different medications, including steroids and allergy shots, but usually the first thing to try is an antihistamine.

How Antihistamines Treat Allergies

When your body comes into contact with whatever your allergic trigger is -- pollen, ragweed, pet dander, dust mites, for example -- it makes chemicals called histamines.  They cause the tissue in your nose to swell (making it stuffy), your nose and eyes to run, and your eyes, nose and sometimes mouth to itch. Sometimes you may also get an itchy rash on your skin, called hives.  

Antihistamines reduce or block histamines, so they stop allergy symptoms.

Antihistamines work well to relieve symptoms of different types of allergies, including seasonal (hay fever), indoor, and food allergies, but they can't relieve every symptom. To treat nasal congestion, your doctor may recommend taking a decongestant. Some drugs combine an antihistamine and decongestant.

What Types of Antihistamines Are Available?

Antihistamines come in different forms, including tablets, capsules, liquids, nasal sprays, and eyedrops. Some are only available by prescription. Others you can buy over the counter (OTC) at your local pharmacy.

Examples of prescription antihistamines include:

  • Astelin, Astepro (azelastine) nasal sprays
  • Atarax, Vistaril (hydroxyzine)
  • Clarinex (desloratadine)
  • Cyproheptadine (generic only)
  • Emadine (emadastine) eyedrops
  • Livostin (levocabastine)  eyedrops
  • Optivar (azelastine) eyedrops
  • Palgic (carbinoxamine)
  • Xyzal (levocetirizine)

Examples of OTC antihistamines:

  • Allegra (fexofenadine)
  • Benadryl (diphenhydramine)
  • Dimetane (brompheniramine)
  • Claritin, Alavert (loratadine)
  • Tavist (clemastine)
  • Chlor-Trimeton (chlorpheniramine)
  • Zyrtec (certirizine)

Eyedrops likes Emadine and Livostin treat symptoms of eye allergies, including itchy, watery eyes. Some medications, like Allegra-D, Claritin-D, and Zyrtec-D, combine an antihistamine and a decongestant to relieve congestion.

Side Effects of Antihistamines

Antihistamines can cause side effects, and some cause more side effects than others. Drugs such as Benadryl, Chlor-Trimeton, and Tavist and belong to an older group known as "first-generation" antihistamines. They tend to cause more side effects, particularly drowsiness.

Newer-generation antihistamines such as Allegra, Clarinex, and Zyrtec and have fewer side effects, so they may be a better choice for some people.

Some of the main side effects of antihistamines include:

  • Dry mouth
  • Drowsiness
  • Dizziness
  • Nausea and vomiting
  • Restlessness or moodiness (in some children)
  • Trouble urinating or not being able to urinate
  • Blurred vision
  • Confusion

If you're taking an antihistamine that causes drowsiness, try to take it before bedtime. Don’t take it during the day before driving or operating heavy machinery.

Read the label before you take an allergy drug. Antihistamines may interact with other medications you are taking.

Talk to your doctor first if you have an enlarged prostate, heart disease, high blood pressure, thyroid problems, kidney or liver disease, a bladder obstruction, or glaucoma. Also check with your doctor if you are pregnant or nursing.

WebMD Medical Reference

Reviewed by Stanley M. Fineman, MD, MBA on October 21, 2014
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