Fast-acting relief from itchy eyes caused by allergies (pollen, dust, pet dander, grass, etc.) Prescription-strength formula available over-the-counter Works within minutes and provides up to 12 hours of relief Zaditor Antihistamine Eye Drops 0.17 fl oz. Not all eye drops work to relieve symptoms for as long as you need. Zaditor Eye Drops relieve itching for up to 12 hours, which is longer than some other prescription-strength drops currently on the market