"Two things can happen: The drug will start to break down into something not effective or something potentially harmful," Aziz says.
With over-the-counter drugs, it's not a safety issue as much as a potency issue, says Joe Doss, senior vice president and director of public affairs at Nonprescription Drug Manufacturers Association, based in Washington, D.C.
The trade association, which represents 95 percent of the manufacturers of nonprescription medicines in the United States, helps consumers understand how to use over-the-counter medicines safely and effectively, Doss says.
Most over-the-counter medicines carry an expiration date, which is the date beyond which the product should not be used.
The date assures the product meets applicable standards of identity, strength, quality and purity when used, according to U.S. Food and Drug Administration.
Most over-the-counter medications have a two-year expiration date, says Tom McGinnis of FDA's Office of Health Affairs.
The manufacturer must provide data to the FDA to show the product will retain its potency and quality, McGinnis says.
The expiration dates for prescription medications are determined by each state, McGinnis says.
The expiration date is based on the premise that the drug will be staying in the original packaging that comes from the manufacturer, Aziz says. When the drug is removed from the package, it is more susceptible to deterioration, he says.
When to toss?
Keep your medicine supply simple, says Dr. M. Douglas Becker, a Hagerstown pediatrician.
"Everyone has a drawer full of stuff that is outdated," Becker says. "Our complicated, pack-rat lifestyle encourages us to keep things too long."
If an expiration date just includes a month and year, the medication is effective until the end of that month, Aziz says.
He advises consumers to review their medications at least once a year, and dispose of items that are out of date.
"It's amazing how many medications you can accumulate over a year," Aziz says.
Never share your prescriptions with anyone else, and don't take ones left over from a previous illness, Aziz says.
"It's the physician's job to diagnose, and just because you have the same symptoms doesn't mean the medicine will be appropriate. The safest alternative is to get rid of it," he says.
Tips for consumers
Here are a few things to remember when buying over-the-counter medicines:
Always read the package to learn important information such as dosage and storage recommendations, Doss says.
"The key message is to read the label," he says.
Economy sizes aren't always a bargain, and a 500-count bottle of aspirin isn't always the best choice.
If you buy a large bottle, you may be tempted to keep it too long, and if you waste it, you're really not gaining anything, Aziz says.
Make sure that tamper-resistant packaging is intact.
If the product is packaged in shrink wrapping, check to see that it isn't torn, Aziz says.