A drug's expiration date is the date at which the drugs potency decreases to approximately 85%
of its original strength. This expiration is determined by aging studies at elevated
temperatures, in a specific package that is unopened. These are guidelines set by the United
States Pharmacopeia for all manufacturers of drugs in the U.S. It is a requirement for the
manufacturer to label its product with an expiration date.
Once a medication has been dispensed in a light and moisture resistant vial by your pharmacy, common practice is to give this drug an expiration of one year. It is not recommended to take a medication past its expiration date; some breakdown of the drug may occur.