You have probably heard of Ozempic. You may have heard it called a "weight-loss miracle." But what if the most interesting thing about semaglutide — the active ingredient in Ozempic and Wegovy — has nothing to do with waistlines? Researchers at the University of California, Berkeley gave the drug to female mice that were already 20 months old, roughly equivalent to a person in their mid-sixties.

Three months later, the animals were measurably sharper, stronger, and biologically younger than untreated mice of the same age. The lifespan numbers were the detail that stopped scientists in their tracks. Mice that received semaglutide until the end of their lives lived a median of nearly 100 days longer than those that did not — a remarkable gap for a drug that was simply injected into animals whose ageing was already well underway. Gene activity in treated mice also showed reduced inflammation and a better-preserved ability to repair tissue, two hallmarks that researchers associate with slower biological ageing.

The obvious question, of course, was whether calorie restriction was doing all the real work. Because semaglutide suppresses appetite, the team ran a direct comparison: one group received the drug, while another was placed on a 24% calorie-restricted diet designed to mirror exactly what the treated mice were eating. The two approaches overlapped in many ways — but in several important areas, the drug appeared to go further than diet alone. That finding matters enormously.

"If GLP-1 agonists do indeed slow it down, then a wide range of clinical benefits is exactly what you'd expect to see," said Rafael de Cabo, a senior investigator at the NIH's National Institute on Aging.