Deep inside the brain's appetite-control center, NIH researchers have discovered why Ozempic and Wegovy work differently for different people—and why their effects often slow down over time. The discovery opens a surprising window into the cellular machinery behind one of modern medicine's most talked-about weight loss drugs.
Scientists at the National Institutes of Health, led by postdoctoral fellow Claire Gao and senior investigator Michael Krashes, used fluorescence imaging to watch how semaglutide—the active ingredient in Ozempic and Wegovy—affects living brain cells in mice. What they found challenges a simple on-off understanding of how these medications work. Instead of all neurons responding the same way, "cAMP responses across cells varied on a continuum," as Krashes explained. Some cells lit up strongly and sustained their response, while others showed only brief bursts of activity.
The key to the drug's appetite-suppressing power, the team discovered, is a molecule called cyclic adenosine monophosphate, or cAMP, in a brain region called the area postrema. When semaglutide activates GLP-1 receptors on nerve cells, it triggers increased cAMP levels—but the durability of that signal varies dramatically from cell to cell. Some neurons maintain elevated cAMP for extended periods; others quickly return to baseline. This cellular variation may explain why people respond to these drugs so differently, and why weight loss often plateaus after months of steady results.
The finding also hints at why effects fade: some cells appear to dial down their sensitivity by breaking down or internalizing their GLP-1 receptors, essentially becoming less responsive to the drug over time. But the NIH team discovered something encouraging during their experiments. When they used roflumilast—a drug that blocks PDE4, an enzyme that normally breaks down cAMP—they were able to shift more neurons toward longer-lasting responses. That simple intervention in the lab suggests a path forward in drug development.
Andrew Lutas, co-corresponding author and investigator at NIH's National Institute of Diabetes and Digestive and Kidney Diseases, noted that understanding these "nuts and bolts" of cellular mechanics had been a missing piece of the puzzle. "By digging into these mechanisms, we're beginning to answer some of these questions," he said. The implications are substantial. If future GLP-1 treatments could be redesigned to keep cAMP signals elevated longer, patients might need injections less frequently, and people who currently hit weight loss plateaus might break through them instead.
The research does come with caveats. The study observed neurons only for a few hours at a time, a significant limitation. Researchers hope to use newer techniques to track cellular responses over days or weeks, revealing patterns that short-term observations might miss. Much more work lies ahead before any of these laboratory findings translate into new treatments.
Still, the discovery represents a meaningful step toward demystifying one of the most prescribed and discussed medications in the world. By revealing the cellular conversations that drive weight loss, NIH scientists have handed future researchers a map to potentially more effective treatments—and answers for the millions of people for whom these drugs have proven transformative but incomplete.