Fexofenadine (Allegra) is an antihistamine that treats and prevents allergy symptoms. It blocks histamine to reduce your symptoms. 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. Allegra allergy relief medicine starts working in one hour for relief from sneezing, runny nose, itchy and watery eyes, and itchy nose or throat. One pill provides 24-hour allergy relief that doesn’t make you drowsy and affect your normal brain function. Allegra (fexofenadine) is a non-drowsy antihistamine used for seasonal allergic rhinitis and chronic idiopathic urticaria. Compared with first-generation agents, it has minimal CNS penetration and is less sedating, making it suitable for daytime use and tasks that require alertness. The trend, according to Narula, combines the use of Allegra, a drug that's typically used for allergies, and Pepcid, a drug that's typically used for ulcers or acid reflux. Dr. Tara Narula, chief medical correspondent, breaks down the viral trend that some have used to treat menopause symptoms. Allegra allergy relief medicine starts working in one hour for relief from sneezing, runny nose, itchy and watery eyes, and itchy nose or throat. One pill provides 24-hour allergy relief that doesn’t make you drowsy and affect your normal brain function. Want fast, non-drowsy allergy relief? Allegra helps relieve your toughest allergy symptoms, without the drowsy effect, empowering you to live life fully*, everyday. Fexofenadine (Allegra) is a second-generation antihistamine. It blocks histamine, a natural chemical in your body that can cause allergy symptoms like itchiness, itchy eyes, or runny nose. By blocking histamine, fexofenadine (Allegra) helps relieve allergy symptoms. The OTC combo of Allegra and Pepcid for anxiety and depression is going viral on TikTok, but is there any validity to it? We asked doctors. What is Allegra? Allegra (fexofenadine) is an antihistamine used to treat allergy symptoms, including sneezing, itching, watery eyes, and a runny nose in adults and children.