Detailed dosage guidelines and administration information for Allegra (fexofenadine hydrochloride). Includes dose adjustments, warnings and precautions. While some other oral antihistamines may cause you to be drowsy, Allegra® won't. Fexofenadine, the active ingredient in Allegra ®, provides non-drowsy allergy relief with 0% brain interference, relieving allergy symptoms like sneezing, runny nose and itchy eyes. Overview: Fexofenadine is an antihistamine that is taken to help treat allergy symptoms, such as a runny nose, itchy or watery eyes, sneezing, or an itchy nose or throat. Common side effects may. Learn about fexofenadine (Allegra) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. I've been taking these Allegra 24-hour allergy tablets daily to help manage my seasonal allergies, and they've been very effective at keeping my symptoms under control. The once-daily dosing is convenient, and the tablets are easy enough to take with a glass of water. Antihistamines work by preventing the effects of a substance called histamine, which is produced by the body. Histamine can cause itching, sneezing, runny nose, and watery eyes. Also, in some people histamine can close up the bronchial tubes (air passages of the lungs) and make breathing difficult. For your allergy symptoms, nothing works faster* than Allegra Adult 24-Hour Allergy Relief Tablets. This allergy relief medicine comes with a bonus tissue pack and starts working in one hour for relief from sneezing, runny nose, itchy and watery eyes, and itchy nose or throat. Allegra (fexofenadine) is an antihistamine used to treat allergy symptoms, including sneezing, itching, watery eyes, and a runny nose in adults and children. Allegra can also be used to treat hives caused by a condition called chronic idiopathic urticaria in adults and children over 12 years of age. Allegra Allergy 24 hour products temporarily relieve allergy symptoms, including runny nose, sneezing, itchy, watery eyes, and itching of the nose or throat due to hay fever or other upper respiratory allergies to indoor or outdoor allergens. Allegra is a non-drowsy antihistamine for allergy relief. Here’s our guide for dosing Allegra for kids and adults, and what to do if you miss a dose or take too much.