The most effective way to relieve an itchy throat caused by allergies is to take over-the-counter antihistamines, explains WebMD. The main side effect of taking oral antihistamines is an increase in drowsiness.
Most irritated throats that are caused by allergies are due to postnasal drip, notes Healthline. After becoming exposed to an allergen that triggers an allergic reaction, congestion in the sinuses drains down the throat, causing irritation.
Decongestants or nasal sprays may also relieve some symptoms due to postnasal drip, states WebMD. A doctor may also recommend prescription-strength medication if a patient's symptoms are severe or continue for a long period of time, according to Healthline.