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Antihistamines and Your Asthma

What You Need to Know About Antihistamines


Updated June 02, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Antihistimines and Asthma
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While antihistamines are not asthma medications per se, that does not mean your asthma might not benefit from them.

What Are Antihistamines?

If you have a lot of allergy symptoms, your doctor may use antihistamines to help provide relief, as well as get control of your asthma. Histamine is a normal part of your body's defense mechanisms, but when histamine is released in response to an allergen, you may develop allergy symptoms. Antihistamines are available as prescriptions and over-the-counter (OTC) medications.

How Do Antihistamines Work?

As you might expect from its name, antihistamines act against histamine. In asthma and allergies, histamine is released as an overreaction by your immune system to an allergen.

Histamine is released by mast cells and basophils. It can cause symptoms all over your body, depending on where the histamine gets released:

An antihistamine works by preventing mast cells and basophils from attaching to the parts of your body where histamine can be released and cause symptoms.

What Antihistamines Are Available?

When you experience runny nose, sneezing and itchy-watery eyes, you may want to try an OTC antihistamine medication first. Some popular OTC antihistamine medications include:

  • Zyrtec
  • Claritin
  • Benadryl

If you are not able to get your allergy symptoms under control with an OTC antihistamine, your doctor may prescribe one of the following prescription antihistamines:

  • Allegra
  • Clarinex
  • Xyxal

Both the older and newer antihistamines are also available as part of a combination product that contains pseudoephridine.

What Are Common Antihistamine Side Effects?

While most people do not experience side effects when taking an antihistamine, you need to be aware of the potential. First generation antihistamines like brompheniramine (Dimetapp) and diphenhydramine (Benadryl) can make you sleepy. This is because these particular drugs also go to the part of the brain responsible for nausea and vomiting (they can also be used to treat or prevent motion sickness). Second generation antihistamines are less likely to cause this side effect, but are no more effective in controlling symptoms and cost more money. The higher the dose of medication you take, the more likely you will experience side effects. Finally, if you are older than 60 you are at greater risk of becoming drowsy with an antihistamine, and may also have an increased risk for falling.

Additional common side effects include:

Most of these side effects will resolve over time. However, if you experience any of the following side effect consider talking with your doctor:

Additionally, you need to be careful and watch out for side effects if you combine antihistamines with:

Because antihistamines can also react with some antibiotic and antifungal drugs, it is extremely important for every doctor that treats you knows your medications. Make sure you bring the pill bottles with you or at least an up to date list. If you get a new prescription make sure to ask your pharmacist to check to make sure there will be no dangerous interactions.

Finally, talk with your doctor before taking antihistamines if you have any of the following conditions, as they can make some conditions worse:

  • Benign prostatic hypertrophy or an enlarged prostate
  • Breathing conditions such as asthma or copd
  • Heart problems
  • Hypertension or high blood pressure
  • Thyroid problems

Other Medications Your Doctor Might Add If Antihistamines Don't Do The Trick

If antihistamines don't get your allergy symptoms under control and your asthma is still bothersome, your doctor may consider adding the following:


Consumer Reports. Accessed September 17, 2011. Antihistamine Drugs: Summary of Recommendations.

Mayo Clinic. Accessed September 17, 2011. Allergy medications: Know your options

American Academy of Otolaryngology — Head and Neck Surgery. Accessed September 17, 2011. Antihistamines, Decongestants, and Cold Remedies

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