When scientists first created the class of drugs that includes Ozempic, they told a tidy story about how the medications would work: The gut releases a hormone called GLP-1 that signals you’re full, so a drug that mimics GLP-1 could do the exact same thing, helping people eat less and lose weight. The rest, as they say, is history. The GLP-1 revolution birthed semaglutide, which became Ozempic and Wegovy, and tirzepatide, which became Mounjaro and Zepbound—blockbuster drugs that are rapidly changing the face of obesity medicine. The drugs work as intended: as powerful modulators of appetite. But at the same time that they have become massive successes, the original science that underpinned their development has fallen apart. The fact that they worked was “serendipity,” Randy Seeley, an obesity researcher at the University of Michigan, told me. (Seeley has also consulted for and received research funding from companies that make GLP-1 drugs.) Now scientists are beginning to understand why. In recent years, studies have shown that GLP-1 from the gut breaks down quickly and has little …