Antihistamines are medications that block the production of a chemical called histamine, which the body releases as a response to foreign substances — including allergens. Antihistamines help with symptoms including congestion, sneezing, itching, nasal-passage swelling, and itchy or teary eyes. Around 60 percent of asthma cases are triggered by allergy.
There are several over-the-counter antihistamines available, including loratadine (sold under brands including Claritin and Alavert), cetirizine (including Zyrtec), diphenhydramine (such as Benadryl and Nytol), and fexofenadine (Allegra). Some antihistamines are available as prescription-only.
How do I take it?
Antihistamines are available as pills, syrups, capsules, suspensions, and suppositories. Speak with your health care provider as to which type of antihistamine and dosage is best for you or your loved one.
Common side effects of antihistamines include abdominal pain, constipation, dry eyes and mouth, vision changes, headache, drowsiness, dizziness, nervousness or irritability, and sore throat.
Rarely, some antihistamines can cause serious side effects including chest tightness, hives, severe itching, irregular heartbeat, and difficulty urinating.
For more details about this treatment, visit:
Antihistamines — Cleveland Clinic
Antihistamine (Oral Route, Parenteral Route, Rectal Route) — Mayo Clinic
Antihistamines for Allergies — Medline Plus