Antihistamines for Allergies
Allergies bring more than the misery of a stuffy nose, watery eyes, and sneezing. If you don't treat allergies, they can aggravate or lead to other conditions such as asthma and sinusitis.
Treatment for allergies can involve several different medications, including steroids and allergy shots, but usually the first line of attack is with antihistamines.
It's hard enough to cope with allergies on the weekend, but dealing with allergies at work is even more challenging. Ask anyone who's ever dozed off in the middle of an important meeting because of allergy symptoms or medications. "Allergy symptoms are the No. 2 reason adults miss work," says James Sublett, MD, a board-certified asthma and allergy specialist in Louisville, Ky. The average worker with allergies misses about one hour per week over the course of a year. But that sick time is...
Read the Managing Allergies at Work article > >
How Do Antihistamines Treat Allergies?
Antihistamines work by targeting the immune system response that leads to allergy symptoms such as itching and a runny nose. When your body comes into contact with whatever your allergic trigger may be (whether it is pollen, ragweed, or another substance), mast cells of the immune system produce substances called histamines, which act on receptors in your nose and throat. That's what causes the tissue in your nose to swell (producing a stuffy nose), your nose and eyes to run, and your eyes to itch. Sometimes this allergic reaction also triggers an itchy rash on your skin, called hives. Antihistamines reduce or block the action of histamines by preventing them from attaching to their receptors.
Antihistamines are effective at reducing symptoms of different types of allergies, including seasonal allergies (hay fever) and food allergies, but they can't relieve every symptom. To help treat nasal congestion, your doctor may recommend adding 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 antihistamines are only available by prescription; others you can buy over the counter (OTC) at your local pharmacy or supermarket.
Examples of prescription antihistamines include:
- desloratadine (Clarinex)
- levocetirizine (Xyzal)
- carbinoxamine (Palgic)
- cyproheptadine (generic only)
- hydroxyzine (Atarax, Vistaril)
- azelastine (Astelin, Astepro nasal sprays)
- emadastine (Emadine eyedrops)
- azelastine (Optivar eyedrops)
- levocabastine (Livostin eyedrops)
Examples of OTC antihistamines:
- diphenhydramine (Benadryl)
- fexofenadine (Allegra)
- loratadine (Claritin, Alavert)
- chlorpheniramine (Chlor-Trimeton)
- brompheniramine (Dimetane)
- certirizine (Zyrtec)
- clemastine (Tavist)
Allergy eyedrops such as Emadine and Livostin can help specifically with symptoms of eye allergies, including itchy, watery eyes. Some medications contain a combination of an antihistamine and a decongestant to relieve congestion. An example is Claritin-D, which combines the antihistamine Claritin with the decongestant pseudoephedrine.
Side Effects of Antihistamines
Like just about all drugs, antihistamines can cause side effects, and some antihistamines cause more side effects than others. Drugs such as Chlor-Trimeton, Tavist, and Benadryl belong to an older group of antihistamines known as "first-generation" antihistamines. They tend to cause more side effects, particularly drowsiness.
Newer-generation prescription antihistamines such as Clarinex, Zyrtec, and Allegra 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)
- difficulty urinating or inability to urinate
- blurred vision
- confusion
When using antihistamines, follow these precautions:
- If you're taking an antihistamine that causes drowsiness, try to take it before bedtime. Avoid using during the day when driving or operating heavy machinery.
- Before taking antihistamines, go over all of your medications with your doctor or pharmacist. Antihistamines may interact with other medications you are taking.
- Talk to your doctor before using antihistamines if you have an enlarged prostate, heart disease, high blood pressure, thyroid problems, kidney or liver disease, a bladder obstruction, or glaucoma or other conditions that cause a rise in eye pressure. Also check with your doctor if you are pregnant or nursing.
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