Millions of Americans swallow Ozempic or Wegovy each week in hopes of shedding pounds, but Stanford researchers have now documented what many users fear in quiet moments: these weight-loss drugs melt away muscle along with fat, and unlike fat, lost muscle doesn't bounce back easily. The discovery has triggered an urgent search for a solution—and Stanford Medicine scientists may have found one hiding in plain sight: an existing drug already deemed safe by the FDA, currently in clinical trials for a completely different purpose.
Helen Blau, the Donald E. and Delia B. Baxter Foundation Professor and director of the Baxter Laboratory for Stem Cell Biology at Stanford, leads a team whose work addresses what she calls "a major unmet need." Her research over the past several years has zeroed in on a peculiar enzyme called 15-PGDH, which quietly sabotages the body's ability to repair muscle. When this enzyme blocks a crucial metabolite called prostaglandin E2, muscle stem cells—the body's regenerative builders—struggle to activate. In aging bodies, this becomes a compounding problem, but the same mechanism appears to play a role when GLP-1 medications like semaglutide trigger weight loss.
In their new study, published in Proceedings of the National Academy of Sciences, Blau's team fed young adult male mice a high-fat diet for 12 weeks to induce obesity, then treated them with semaglutide, an experimental enzyme inhibitor called a PGDHi, or both for five weeks. The results were striking. Mice treated with semaglutide alone lost about 25 percent of their body weight and substantially reduced their fat levels—exactly as hoped. But their skeletal muscle mass shrank too. More troublingly, when researchers injured these mice's muscles, the animals' ability to repair and rebuild deteriorated markedly.
When mice received both semaglutide and the PGDHi drug together, muscle fiber size was restored and muscles recovered stronger after injury compared with mice on semaglutide alone—and even compared with untreated mice. The PGDHi boosted muscle stem cell proliferation and restored their ability to generate new muscle fibers, essentially preserving the body's muscle-building machinery even while GLP-1 medications accelerated fat loss.
Minas Nalbandian, a postdoctoral scholar and first author of the paper, explains the mechanism simply: "It wasn't just that there was an initial loss of muscle with the GLP-1 receptor agonist—it also reduced the regenerative capacity of the young mouse muscles." The PGDHi reverses that decline by enhancing the regenerative response, allowing muscles to respond robustly to injury or exertion.
Importantly, when researchers gave healthy young mice the PGDHi alone, it produced no effect on muscle strength. This suggests the drug works as a muscle repair amplifier specifically when muscles are damaged or stressed—whether through injury or regular exercise—rather than as a blanket muscle builder.
The implications are significant. An oral form of PGDHi is already in clinical trials to treat age-related muscle loss, meaning researchers are not starting from scratch. If the compound proves similarly safe and effective in humans taking GLP-1 medications, millions could preserve the lean muscle mass that sustains strength, mobility, and long-term health—finally addressing the hidden cost of weight loss.