Opposite actions on the same receptor can promote weight loss by targeting different brain circuits.
Two obesity drugs can push the same brain receptor in opposite directions and still lead to weight loss. Researchers at the University of Cambridge have now traced that apparent contradiction to two separate regions of the brain.
The mouse study, published in Nature Metabolism, found that activating the receptor in the brainstem reduced appetite. Blocking it in the hypothalamus produced a similar result through a different biological route.
Why opposite drugs can both work
More than one billion people worldwide live with obesity, a condition associated with a higher risk of type 2 diabetes, cardiovascular disease, and cancer. Losing weight can reduce these risks, but diet and exercise alone do not work sufficiently for everyone.
A newer generation of weight loss medications targets receptors that influence appetite and blood sugar control. Wegovy and Ozempic, for example, activate a protein receptor called the glucagon-like peptide 1 receptor (GLP-1R).
Some medications also act on the glucose-dependent insulinotropic polypeptide receptor (GIPR). Mounjaro and Zepbound activate GIPR, while MariTide blocks it. Scientists have struggled to explain how stimulating and inhibiting the same receptor can both support weight loss.
Different brain regions resolve the puzzle
Researchers at the Institute of Metabolic Science at the University of Cambridge investigated the question in mice. Their experiments showed that GIPR-activating and blocking drugs work through different parts of the brain. The findings also indicated that both approaches can increase weight loss when paired with certain GLP-1-based medications.
To identify the brain regions involved, the researchers genetically modified mice so that GIPR was absent from selected areas. One group lacked the receptor in the brainstem, the region near the top of the spinal cord that helps regulate appetite and nausea. Another lacked GIPR in the hypothalamus, which plays a central role in controlling hunger and body weight. A third group consisted of unmodified mice.
The researchers gave the animals different combinations of a GIPR agonist (which activates the receptor), a GIPR antagonist (which blocks it), and a GLP-1 drug. They then tracked food intake, body weight, fat mass, blood sugar regulation, and brain activity.
The brainstem drives appetite suppression
Comparisons among the three groups revealed that GIPR agonists reduce appetite and body weight by acting through the brainstem.
GIPR antagonists worked through the hypothalamus instead. Blocking the receptor there removed a biological restraint that normally limits how strongly the brainstem responds to signals of fullness.
GIPR blockade also appeared to strengthen the effects of experimental drugs aimed at the amylin receptor. This suggests that GIPR antagonists might enhance several categories of anti-obesity medication, although further research is needed.
A roadmap for stronger drug combinations
The results help explain the effectiveness of MariTide, which combines GIPR antagonism with GLP-1 receptor activation and is currently being tested in phase 3 clinical trials. They may also help researchers design more effective combinations of weight loss drugs.
Dr. Jo Lewis, the study’s first author from the Institute of Metabolic Science at the University of Cambridge, said: “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, and which might work in combination with other obesity medicines to even greater effect.
“Our work also strengthens the idea that the brain is central to obesity treatment. Obesity drugs are not acting simply on the gut or pancreas. Instead, they have important effects on specific, identifiable brain circuits that regulate appetite and food intake.”
Reference: “Distinct brain regions mediate regulation of food intake in response to GIPR agonism or antagonism” by Jo Edward Lewis, Mireia Montaner, Danae Nuzzaci, Paula-Peace James-Okoro, Norio Harada, Nobuya Inagaki, W. Scott Dodson, Patrick J. Knerr, Jonathan D. Douros, Fiona Mary Gribble and Frank Reimann, 24 July 2026, Nature Metabolism.
DOI: 10.1038/s42255-026-01575-z
The research was funded by the Medical Research Council and Wellcome.
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