Cambridge Scientists Solve Mystery of Brain Switch Behind Two Opposite Weight-Loss Drug Types
CAMBRIDGE, England — Scientists at the University of Cambridge say they’ve figured out why two totally opposite drug strategies, aimed at the same brain receptor, both end up helping people lose weight.
It’s a strange puzzle that’s been nagging obesity researchers for years. Some weight-loss drugs turn a certain brain receptor on. Others turn the exact same receptor off. And somehow, both work. The new study, published August 14 in Nature Metabolism, explains why — and it could help drugmakers build better, more targeted treatments with fewer side effects.
More than 1 billion people worldwide live with obesity, according to the researchers, putting them at higher risk for type 2 diabetes, heart disease and cancer. Diet and exercise alone often aren’t enough, which is part of why drugs like Wegovy and Ozempic have exploded in popularity over the past few years.
Those two drugs work by activating a receptor called GLP-1R. But a newer class of medications also targets a second receptor, known as GIPR. And here’s where things get weird: drugs like Mounjaro and Zepbound activate GIPR, while a newer drug called MariTide blocks it. Both, somehow, lead to weight loss.
To find out why, the Cambridge team — based at the university’s Institute of Metabolic Science — used genetically engineered mice. They removed GIPR from different parts of the brain, one region at a time, to see exactly where the effects were coming from.
Turns out, location is everything. Switching GIPR on in the brainstem cut the mice’s appetite. But blocking GIPR in the hypothalamus did something different — it released a kind of internal “brake” that normally holds back fullness signals. Once that brake came off, the mice felt full sooner.
“Understanding which brain circuits respond to these medications — and how they do so — could help us design better drugs that produce more weight loss with fewer side effects,” the Cambridge researchers said.
Two separate paths. Same outcome: less eating, more weight loss.
There’s a bonus finding, too. The team discovered that combining either type of GIPR drug — the activators or the blockers — with GLP-1-based medications produced an even bigger effect than either drug alone. That detail matters a lot for drug companies, since combination treatments are already a hot area of obesity research.
So far, this work has only been done in mice, not humans. Scientists still need to confirm the same brain circuits behave the same way in people before any of this changes how doctors prescribe obesity drugs. But the researchers say mapping these separate brain pathways gives drugmakers a much clearer target — instead of guessing why a drug works, they’ll know exactly which circuit it’s hitting, and why.
That kind of precision, several scientists outside the study noted, is exactly what the next generation of obesity treatments has been missing.
