Fexofenadine hydrochloride 180 is a 180-milligram dose of an antihistamine that is an active ingredient of Allegra, an allergy medication, states RxList. The substance, a white powder, is formulated with other ingredients into tablets to be taken orally. Side effects include symptoms resembling the flu.
Fexofenadine hydrochloride 180 can cause an allergic reaction, which is a medical emergency. Patients need to get help right away if they experience swelling of the face, lips, tongue or throat, difficult breathing or hives, notes RxList. Less serious side effects include nausea, diarrhea, drowsiness, headache or muscle pain. Patients who experience side effects need to stop taking the medication and contact a doctor.