In general, there is no cure for allergies, but there are several types of medications available — both over-the-counter and prescription — to help ease and treat annoying symptoms like congestion and runny nose.

These allergy drugs include antihistamines, decongestants, combination drugs, corticosteroids, and others.

Immunotherapy in the form of allergy shots or pills under the tongue, which gradually increase your ability to tolerate allergens, are also available.

Antihistamines
Antihistamines have been used for years to treat allergy symptoms. They can be taken as pills, liquid, nasal spray, or eye drops. Over-the-counter (OTC) antihistamine eye drops can relieve red itchy eyes, while nasal sprays can be used to treat the symptoms of seasonal or year-round allergies.

Examples of antihistamines include:

Over-the-counter:Cetirizine (Zyrtec), fexofenadine (Allegra), levocetirizine (Xyzal), and loratadine (Claritin, Alavert) are taken by mouth. Brompheniramine (Dimetapp allergy, Nasahist B), chlorpheniramine (Chlor-Trimeton), clemastine (Tavist), and diphenhydramine (Benadryl) can make you drowsy. Ketotifen (Zaditor) and naphazoline and pheniramine combination ophthalmic (OcuHist) are eye drops.

Prescription: Desloratadine (Clarinex) is a medication taken by mouth. Azelastine nasal (Astelin) is a prescription nasal antihistamine spray. Prescription antihistamine eye drops include azelastine ophthalmic (Optivar), epinastine ophthalmic (Elestat), and olopatadine ophthalmic (Patanol).
How Do Antihistamines Work?

When you are exposed to an allergen — for example ragweed pollen — it triggers your immune system. People with allergies demonstrate an exaggerated immune response. Immune system cells known as “mast cells”release a substance called histamine, which attaches to receptors in blood vessels, causing them to enlarge. Histamine also binds to other receptors causing redness, swelling, itching, and changes in secretions. By blocking histamine and keeping it from binding to receptors, antihistamines prevent these symptoms.