The best way to know is by checking the expiration date on the box or bottle of the medication. Most medicines stored under reasonable conditions will retain some of their potency for a short time past the expiration date. Drug companies use these dates to indicate the period of time after which they can no longer guarantee the efficacy of the medicine. Just like anything else, it is advisable to routinely update your medicine cabinet and replace medicines that have expired with a new supply.
– David Fox, MD, primary care physician, Northwestern Medicine Primary and Specialty Care Lavin