If medication is past its expiration date, discard it and replace it with new product, says the makers of Benadryl. However, many medications are safe and effective well past their expiration dates, according to The Allergy Clinic.
The expiration dates on bottles of medicine are the latest date at which the manufacturer is willing to guarantee safety and potency. When the date passes, nothing happens to make the medicine lose its effectiveness, explains The Harvard Medical School Family Health Guide. Many drugs, especially those stored in their unopened, original containers, can stay potent for years after their expiration dates. However, it can be difficult, if not impossible, to tell what changes have occurred in a medication. Therefore, it is best to discard expired medication or at the very least ask a doctor or pharmacist before taking it.