Scientists haven't found the fountain of youth, said Keith J. Winstein in The Wall Street Journal, and you won't be able to buy a "reliable human longevity pill" any time soon. But a study published Wednesday in the journal Nature "found that rapamycin, a drug used in organ transplants, increased the life span of mice by 9 percent to 14 percent, the first definitive case in which a chemical has been shown to extend the life span of normal mammals."

Another promising aspect of the find, said Gisela Telis in Science, was that the antibiotic rapamycin—first found in soil samples from Easter Island in 1965—"enabled middle-aged mice to live up to 16 percent longer than their rapa-free counterparts." That doesn't make rapamycin the fountain of youth, but the discovery marks the first time a drug has been shown to lengthen life span in mammals, even when administered late in life."

That's encouraging, said Nicholas Wade in The New York Times, because "other interventions that prolong life in mice, including a very low-calorie diet, need to be started early in life to show any effect." But doctors warn that rapamycin can have dangerous side effects—it is used to suppress the immune system in transplant patients. A drug like that is "not to be trifled with," so don't try this at home.