I'm assuming this is a suspension (liquid), since I don't believe that's available in pill form. Expiration dates on medications are really just guidelines. They're usually about 1-2 years from production, and represent the date that the manufacturer "guarantees" effectiveness. Some meds, (not all) start losing effectiveness over time, anywhere from 5-50%. Since it's a liquid, I think it's more prone to chemical changes than a pill would be. It won't hurt you... but it may not be as effective as it would have been when fresh. Double check with your pharmacist, but I've used cough syrup with codeine over 2 years past the expiration date with no problem and gotten the full effect.