(CNN) - If you toss out medication as soon as it expires, you might be jumping the gun.
A researcher with the University of California, San Francisco found that most drugs are still potent 40 years after their expiration dates.
Two of the drugs tested, aspirin and amphetamine, did consistently fall below the government's threshold for active ingredients.
Most drugs expire one to five years after they're made, and the study's author says if we prolonged their shelf lives it could save patients hundreds of dollars a year.
But, before you dig your past-date pills out of the garbage, one professor has a warning.
He says the drugs in this study were stored unopened for all those years, and that similar drugs stored in other conditions might have a different outcome.
The study appears in the Archives of Internal Medicine.