Oral medications (i.e., taken by mouth) for allergic rhinitis include antihistamines and decongestants.

Oral medications for allergies available in Canada include:

  • non-prescription
    • antihistamines
    • antihistamine and decongestant combination products
      • cetirizine - pseudoephedrine (Reactine® Allergy & Sinus)
      • deslorataine - pseudoephedrine (Aerius® Dual Action)
      • fexofenadine - pseudoephedrine (Allegra-D®)
      • loratadine - pseudoephedrine (Claritin® Allergy & Sinus)
      • triprolidine - pseudoephedrine (Actifed®)
    • decongestants
      • pseudoephedrine (Eltor®, Sudafed® and others)
  • prescription
    • leukotriene receptor antagonists

Antihistamines work by stopping the action of histamine, which is a substance in your body that causes an allergic response when you are exposed to an allergen. Antihistamines reduce the symptoms of eye itching, nasal itching, runny nose, sneezing, and watery eyes, while oral decongestants help with nasal congestion. Desloratadine is an antihistamine that also relieves nasal congestion. Antihistamines and oral decongestants can be used together to relieve allergy symptoms.

The third type of oral allergy medications is leukotriene receptor antagonists (montelukast), which work by blocking leukotrienes. Leukotrienes are chemicals that are released by your body during an allergic response. They are also involved in causing allergy symptoms.

Side effects of oral medications

  • The side effects of antihistamines may include dry mouth, constipation, drowsiness, difficulty urinating, and decreased reaction time. At normal recommended doses, cetirizine, desloratadine, fexofenadine, and loratadine have fewer side effects than other antihistamines.
  • The side effects of decongestants include headache, dizziness, dry mouth, palpitations (rapid, irregular heartbeat), tremor, and trouble sleeping. Normal doses of oral decongestants can also increase the blood pressure in people who have high blood pressure. People who have severe or poorly controlled high blood pressure should not take oral decongestants.
  • The most common side effects of montelukast include diarrhea, stomach pain, headache, thirst, itchy skin, and rash.

Some oral medications may affect people with certain medical conditions (including high blood pressure, glaucoma, and low thyroid) and may not be a suitable treatment option. To ensure that you are taking the most appropriate medication, inform your doctor and pharmacist of any other medications you are taking and any medical conditions you have.

You should follow your doctor's and pharmacist's instructions on taking the medication to ensure you get the most benefit from it. If you are taking any of these medications and your allergy symptoms do not go away completely, talk to your doctor.