FDA regulations do not require manufacturers to determine actual long-term drug potency and stability.For example, if a company chooses a three year expiration date, it does not have to test beyond that for prolonged effectiveness. Medication's potency gradually decreases starting from the moment of it's manufacture This process is not in anyway spontaneous after the expiry date.S., since the patent term now depends on the priority date, not the issue date.

Updated: April, 2017 Many medications are very expensive and people hate to waste them.
To avoid a costly visit to the doctor for a new prescription, many people have to consume expired drugs.
The box of prescription drugs had been forgotten in a back closet of a retail pharmacy for so long that some of the pills predated the 1969 moon landing.
Most were 30 to 40 years past their expiration dates — possibly toxic, probably worthless.
Design patents filed on or after May 13, 2015 have a term of 15 years from issuance.
The original patent term under the 1790 Patent Act was decided individually for each patent, but "not exceeding fourteen years". 117, 119, 5) provided (in addition to the fourteen-year term) an extension "for the term of seven years from and after the expiration of the first term" in certain circumstances.
Physicians and pharmaceutical companies, because of legal restrictions and liability concerns, will not sanction such use and may not even comment on the safety or effectiveness of using their products beyond the date on the label. The expiration date, required by law in the United States, beginning in 1979, indicated the date the manufacturer guarantees the full potency and safety of the drug.
At the time of the medication expiry date, the drug must be at least 90% of the original potency under proper storage conditions.
Pharmacies across the country — in major medical centers and in neighborhood strip malls — routinely toss out tons of scarce and potentially valuable prescription drugs when they hit their expiration dates.
Gerona and Cantrell, a pharmacist and toxicologist, knew that the term “expiration date” was a misnomer.
But to Lee Cantrell, who helps run the California Poison Control System, the cache was an opportunity to answer an enduring question about the actual shelf life of drugs: Could these drugs from the bell-bottom era still be potent?