How fast does allegra (fexofenadine) work?

20-30 minutes: Oral antihistamines like Allegra (fexofenadine) need to be absorbed by the digestive system and distributed thru the body before they are effective--about 20-30 minutes. This lag time is usually acceptable for minor allergy symptoms. But if you have asthma, swelling in the throat, or anaphylaxis, taking a quick-acting rescue med like Epinephrine or albuterol can be life-saving. Ask your doctor for more info.

Allegra: Allegra usually starts working within an hour.