Do drugs really stop working after the date stamped on the bottle? Fifteen years ago, the U.S. military decided to find out. Sitting on a $1 billion stockpile of drugs and facing the daunting process of destroying and replacing its supply every two to three years, the military began a testing program to see if it could extend the life of its inventory. The testing, conducted by the U.S. Food and Drug Administration, ultimately covered more than 100 drugs, prescription and over-the-counter. The results ... show that about 90% of them were safe and effective far past their original expiration date, at least one for 15 years past it. The program's returns have been huge. The military from 1993 through 1998 spent about $3.9 million on testing and saved $263.4 million on drug expense. In light of these results, a former director of the testing program, Francis Flaherty, says he has concluded that expiration dates put on by manufacturers typically have no bearing on whether a drug is usable for longer. Manufacturers put expiration dates on for marketing, rather than scientific, reasons," says Mr. Flaherty, a pharmacist at the FDA until his retirement last year. "They want turnover." Joel Davis, a former FDA expiration-date compliance chief, says that with a handful of exceptions - notably nitroglycerin, insulin and some liquid antibiotics - most drugs are probably as durable as those the agency has tested for the military. "Most drugs degrade very slowly," he says. "In all likelihood, you can take a product you have at home and keep it for many years." Drug-industry officials ... acknowledge that expiration dates have a commercial dimension.